Thursday, December 31, 2009

3G Microcell - fun while it lasted

As you're aware, if you've been following along, when we went to the AT&T store in San Diego, we told them we were from out of town and the sales unit typed our home address here in Santa Clara into the computer and assured me that when I got the unit back home I could put in that address and it would be fine.

And, for a week, it was.

Apparently, that was a bug. A bug that AT&T fixed sometime before last night. As of now, I am no longer allowed to register our address here in Santa Clara with the microcell. And without it being located at the address to which it is registered, the GPS check fails and it emulates a doorstop.

I called up AT&T this morning and their plan of record is now to have me ship the unit back to San Diego for a refund.


There is a 30 day refund policy. If the unit is going to be made available in less than 3 weeks, I'd rather just keep it. But naturally, they refuse to "discuss future availability." I could understand not issuing advanced press releases, but these are extenuating circumstances. I cannot possibly believe that there is nobody up the food chain that has a clue as to even approximately when they'll roll these out.

Besides, they've been "testing" the microcells for, what, 9 months now? They work. Really well. Just flip the goddamn switch, AT&T!

Wednesday, December 30, 2009

3G Microcell, more day-to-day info

So it's been a few days since we got home and the microcell is still working perfectly. We haven't tried really abusing the upload bandwidth while a call was in progress. The same carve-out that was in place for Vonage on our server is still in place, so that should be sufficient.

I had an opportunity to test the call hand-off this morning. I called the USNO master clock (202-762-1401) in the driveway while the M-Cell logo was on the phone. I stayed on the call (via bluetooth, not with the phone up to my head) until I had driven about a half mile away. The call got a little spotty very briefly as I got a little bit away from the house (mostly because the coverage near our house is not so good), but the call was handed off. While the call was still going, the M-Cell logo stayed in place on the screen, despite the fact that the phone was well out of range and had handed off to the network proper. As soon as I hung up, and the call was ended, the logo reverted to the usual AT&T one. This likely is the phone's way of letting you know that if you have the unlimited calling plan that the call is still free.

When you fire up the Google maps app on the phone and then click the 'location' button, typically what happens is that the phone uses cell tower triangulation to get an approximate fix, then the assisted GPS functionality refines that down to a point. When the phone is in range of the microcell, it's clear that the microcell's GPS receiver has an impact on that initial triangulated fix - the dot starts up being in the right spot with a house-sized circle around it, then when the phone's GPS kicks in, the circle shrinks down to nothing.

One thing that's a little bit of a let-down for a techie guy like me is that the microcell is a bit of a black box. The status lights on the front don't ever change, and so far as I have found, the box has no open TCP listening ports, so it doesn't have an HTTP server or anything of that sort. It's the quintessential Internet appliance in that regard. It would have been slightly more fun had it had some sort of configuration or status UI. Apart from the blinking status indicators while it's booting up and activating, it doesn't do anything visible at all. Since there's no way to configure the box, it's likely that it requires a DHCP server in order to function (this is in contrast to lots of appliances that use DHCP by default, but allow manual overrides with a configuration GUI). This would have been an issue a while ago had I chosen to deploy the box to the outside network instead of behind the NAT, since it used to be that the outside LAN had no DHCP server. That has since changed, but if you have a completely manually configured network (likely a rarity nowadays), you may have some trouble.

It has had no trouble receiving a GPS signal, so far as I can tell, despite being pretty close to the center of the house. There is a window nearby, so it's conceivable that that helps, though probably the bigger factor is that above the unit is just a drywall ceiling, a layer of cellulose insulation, and a plywood and asphalt shingle roof. Wandering around inside with a Garmin tends to work most of the time. The box has a GPS antenna jack on the back, though at the moment there's no documentation about it, nor is there any mention on AT&T's site about an accessory antenna you can buy and situate closer to a window, if required. I assume that when the nationwide roll-out happens they might offer one.

Since the box plugs into AC power, it will die if there's a power failure. The network infrastructure here is on a UPS, but unfortunately it's also located out in the garage. I wanted the microcell a little bit more centrally located than that, since the path from the garage to the office goes through a lot of walls. One workaround I have used before is to cobble together a power-over-Ethernet solution - a pair of specially modified Ethernet cables that break out one pair to pass power. Then just set up one continuous Ethernet path from the back of the garage to the dining room (this is easier than it sounds), plug the power plug from one hack-cable into the microcell, plug the wall-wart into the socket hooked up to the other hack-cable, and then plug the wall-wart into the UPS.

Thursday, December 24, 2009

3G Microcell

The AT&T 3G Microcells are for sale in San Diego, and coincidently, we're down there for the holidays. I went to one of the stores that was selling them, and despite being told we were from out of town, they were happy to sell us one. Registering it online was simple, although it did take about a half an hour for it to complete its setup and become active. During that time, you can't help but wonder if it is going to succeed. It needs to get good GPS reception before it will fire up. But once it did, the coverage at our parents' house was quite good upstairs. It was a bit more spotty downstairs, but once we get home I am fairly confident that the coverage should fill our smaller house. The web page at the AT&T site that manages the microcell allows you to put multiple physical addresses in and pick which one is the active one. You must put an address in, and the device's GPS will verify that it's accurate or it will refuse to work.

Normally you'd install the microcell someplace where you already have WiFi, so the fact that the microcell does 3G data is kind of moot. There are some points of interest, however, that make pondering the trade-off worthwhile. With WiFi turned off, I get a fairly consistent result from speed tests: a little less than 1 MB/sec down and about 60 Kbps up. WiFi here at my parents' house in San Diego gets easily 5 MB down and 2 or 3 up (their cable modem service is amazing - like, 15 MB down and sometimes 5 up). However, with WiFi, you're typically behind a NAT, and if you use 3G, you get a public address - even though you're using the microcell. Of course, apps that require local connectivity, like the iTunes remote app, won't work through the microcell because of that (you'll have to use WiFi).

I've made a number of calls through the microcell now, and they all sound as good as a cell phone can get. When we get back to Santa Clara, the uplink bandwidth will be a bit more constricted than it is here, but given that Vonage works ok, I would think the microcell will work just as well.

Update - 12/27

We got back tonight. Before leaving San Diego, I powered off the microcell and changed the address on the unit to our home address here in Santa Clara. When we got back home, the microcell took about a half an hour to come back up. When it did, we got the activation text message again, just like after the first activation. As I predicted, the coverage is just what I had hoped - 5 bars throughout the house and all around our property. Unfortunately, there is no unlimited minutes offer outside of the test markets, so we're not getting any breaks on our plan minutes. But hopefully that will change when the nationwide rollout starts. I suspect that the various test markets are really about testing the price points for those plans rather than any technical issues.

Sunday, December 20, 2009

Really, NFL?

We're close to the playoffs. And of all of the games this weekend, there is one that is the most important.

The Chargers are hosting the Bengals at home. The Chargers are one game ahead of the Bengals in the drive for the 2nd AFC playoff seed - which means a first round bye.

In the latter part of the season, the NFL and the networks have the opportunity to "flex" the schedule - to make a more important game the Sunday night game, relegating what was scheduled in the pre-season back to Sunday afternoon (or morning).

So it didn't occur to anybody that this crucial game is worthy of being played on Sunday night? They think Vikings - Panthers is more important somehow? Really?! The Vikings are almost assured of either the #1 or #2 seed in the NFC and the Panthers are all but mathematically eliminated. Who gives a shit?

The only other game even close to how important that game is is the Eagles and 49ers. The 49ers need a win to even have a chance at a wildcard spot, while the Eagles are almost assured of the number 3 seed in the NFC. Of course, since the 49ers are the home team here, it'll be on Fox for sure.

The wrinkle is that the weather has screwed up the game schedules on the East coast. So potentially, the CBS morning game might have been the Chargers', but now that game will be played at the same time as the Raiders @ Broncos. Another "who cares?" game. But it's moot - Fox got the doubleheader today anyhow. Their rejiggered schedule today will give us the 49ers game in the afternoon, and of all of the remaining morning games to show us, they picked... Cardinals / Lions?! Does anybody honestly think the Lions have a shot at their third win this week?

Perhaps the single most important football game of the entire season. None for you!

Saturday, December 19, 2009

Epic win

Look what I saw today:

The bumper sticker is available at I Park Like An I can neither confirm nor deny any information concerning how the sticker got there.

Friday, December 18, 2009

Crossing the anti-spam Rubicon

I've resisted it for a while now, but it's time.

I have added the first DNS TLD to my spam filter.

I have yet to get a single e-mail that wasn't spam from any domain under .info. Not one. It's proven to be one of the best positive indicators of spamminess I've seen in a while now.

There are some .info websites out there that are, well, informative. Which is good. But if anyone can list any legitimate source of e-mail in the entire .info zone, then list it in the comments. Because I ain't seen one yet. And as things stand now, I never will.

Saturday, December 5, 2009

There! I fixed the backyard gate!

We used to have a nice handle and lever style latch on our backyard gate. It was very attractive, and allowed operation from both sides. The problem was that it turns out it wasn't dog proof. Our new dog, Luna, was able to "bonk" into the gate and get it to flip open. She escaped into the world a couple of times, only to have neighbors return her. That's rather embarrassing, so that gate latch had to go.

Everyone has seen the standard kind of gate latch. It consists of a horizontal bar that attaches to the door (if it's inward-swing), and a metal bracket with a slot for the bar to fit into and a hinged metal piece that goes up and down to lock the bar in. It's serviceable, and (at least in our case) dog-proof. The difficulty is that it has no provision for operation from the outside.

Well, not quite. There is a small hole in a tab on the latch that you're supposed to tie to a piece of string run through a hole in the fence. We've all seen those, and the various failure modes.

If the string in any way restricts the free movement of the latch, the whole mechanism is bound to fail. And, of course, in this case, the failure mode is unlatched, dog-roaming mode. Even if the string works, it won't work for long - the wood fence material will no doubt shred the string before too long.

Well, you could attach a wire instead of the string. The problem there is that a solid wire is even more likely to impede the free movement of the latch.

No, what you need is a frictionless, low profile linkage between the cable and the latch.

What you need, is a fairly standard part from the RC model hobby industry: A clevis linkage. A clevis linkage is a small pair of long, thin metal plates that normally sit parallel to each other. At one end of each, there is a round grommet through which you run the cable and either crimp or solder to permanently attach the linkage to the cable. At the other end of one of the parallel plates is a pin, and at the end of the other plate is a hole inside which the pin sits.

Solder a foot long (or so) piece of 1/16" braided cable in the clevis, and use a crimp coupling to form a finger loop at the other end. Drill a 1/4" hole right behind the top of the latch. Run the clevis coupling end of the cable through the hole and attach the clevis pin to the latch.

I have to admit, I didn't come up with this idea myself. We used to have this same problem on our other gate - the string wore out almost immediately, and I was just used to reaching over the fence (I am tall enough) and flipping the latch by hand, but that didn't help Scarlet. So one day while I was in our local hardware store, they had a display for a gate latch improvement kit. It was virtually identical to what I've described above, except that their kit also included a very, very large spring intended to go between the gate and the latch to help insure closure, and a washer with a flange that was meant to sit in the hole and hold the base of the spring centered around the cable hole.

I'd heartily endorse that kit, except that the local hardware store doesn't carry that product anymore, and nobody else has ever heard of it.

The other problem is that while that kit worked flawlessly on the gate where I installed it, a quick test shows that it wouldn't have worked quite so well on this gate. The issue here is that the latch is installed on a 2x4, but the hole you drill for the cable is above that 2x4. That means that the washer / spring base would sit a good two inches behind where it's designed to. I'd either have had to build up the face of the fence at that spot so that the hole emerged "at grade" or modified the kit's spring somehow. But that implies I would have had the kit to start with - I didn't.

Instead, it appears that, at least in this case, the spring is unnecessary. Of course, YMMV.

Wednesday, December 2, 2009

That didn't take long

They kept telling me that if I voted for John McCain that we'd seen escalation in the US military presence in the middle east. I did vote for McCain, and sure enough!

Sunday, November 29, 2009

Trivia: World's first powered vehicle?

In the modern world, people and goods are transported across distances by a wide variety of power systems, from internal combustion, to electrical, to rocketry, and animal (including human) power.

The first non-human powered transport was domesticated animal power, of course, reaching back into pre-history. Potential energy machines, such as spring powered engines simply store human power (when you wind up the spring), so they don't change the timeline at all.

No, to find the first example of a non-animal powered transportation system, we have to look for the first such system that operated under its own power.

If you count systems where all of the energy is expended at the beginning of the journey, then we can include the development of firearms. But if we restrict the field to systems where motive power is applied throughout the journey, then the Chinese experimentation with rocketry in the 13th century is where we have to begin. If we further restrict the field to vehicles that aren't single-use (I don't believe the Chinese ever flew a refuel-able rocket), then we will arrive at steam powered vehicles. And the first one ever was a toy built for the Chinese emperor in 1672. Once again, China figures into the history of transport.

Saturday, November 28, 2009

Power outage

Well, the electric power has been out for, oh about an hour now. I'm able to do this because I have a UPS on the wifi and a battery in my laptop.

I tried calling the electric department at the city to get more information. They had the usual byzantine DTMF phone tree, which led to two recordings that said absolutely nothing whatsoever, except that there was a power outage. Which I knew, or I wouldn't have called in the first place. To quote Bill Murray in the movie Quick Change, "you could have been helpful, but you've been... so much more."

It's almost 2010. With all of the computer technology available, you want to tell me that when there's a power outage the utility has no way to know immediately where it is, at the very least?!

Wednesday, November 18, 2009

Money down the drain

The Capitol Corridor folks spent nearly a million dollars retrofitting one of their locomotives to emit less particulate matter.

You want to really do something about diesel locomotive emissions? How about electrifying the lines? Not only would that eliminate locomotive emissions (yes, there would be power-plant emissions instead, to the extent that non-emitting power sources - like solar, wind and nuclear - don't get used to generate the power), but it would allow deployment of EMU consists that would be able accelerate much better, meaning a faster journey, making the trains more attractive for commuters.

But instead, that's a million dollars we now don't have to electrify the lines or, better yet, to start high speed rail service. Congrats!

Saturday, November 14, 2009

FreeBSD 8.0

I upgraded quack to FreeBSD 8.0 RC3 this evening. I also re-enabled the journaling on /home. The last time I tried the journaling for UFS, it was very unstable. Hopefully in the interim, things have gotten better. If I don't post bad news, then you'll all know it went well.

The only other minor upgrade gotcha was that the APC daemon that monitors the UPS failed. All I had to do was change the device name and rebuild the port and it worked once again.

Wednesday, November 11, 2009

Apple and China

So, how is it that the same company that did this is responsible for helping the Chinese government spread propaganda?.

So 1984 wasn't like 1984. How about 2009?

The Chinese people have a long, storied and glorious history. They deserve so much better than the Maoist goon squad they have running the place now.

Sunday, November 8, 2009

And now, the portfolio is complete

Over the course of a poker lifetime, I think all players who play enough can expect to experience every possible way they can get cold-decked. It doesn't take too long for the nut flush to be beat by a full house. With a little more experience, you're bound to wind up getting hit by set-over-set. But the really esoteric ones are much less likely. Specifically, winding up with the sucker straight-flush (that is, a 3 card straight-flush on board, you have the bottom two, your opponent has the top two), or with the under-quads.

I've already experienced losing with a straight-flush. And last night, I got fed the under-quads.

Now, to be fair, I was playing Chinese Poker with Evan. When you get dealt a quarter of the deck, quads are a bit more likely to happen. But this was quad Jacks under quad Queens.

I just don't know. It's a cruel universe that gives me the skill set to understand the game as well as I do, and then continually feed me shit sandwiches.

Saturday, November 7, 2009

What exactly is being safeguarded here?!

It's commonplace nowadays to buy bottles and jars of stuff from the grocery store and find a seal attached to the top of the bottle underneath a screw-on top.

Now, it's annoying to have to remove the spout from the jar, remove the seal an reattach the spout the first time you use it (as opposed to removing, say, a shrink-wrap plastic wrapper around the spout/cap). But you can sort of understand it. The seal is like the lid of a canning jar - it's a hermetic seal that preserves the contents from spoilage.

The trend sort of started with the Tylenol poisoning scares in the 1980s, and what became a seal against spoilage gained a second purpose as a protection against product tampering.

But the concept falls really, really flat when the product being protected is DISHWASHER DETERGENT!!!!

Thursday, November 5, 2009

Ordinary ergonomics

I'm continually astonished by the poor ergonomics of every day items. It's as if people don't actually try the things they create and put into the marketplace.

Today's example, believe it or not, is Betty Crocker's Dark Chocolate brownie mix.

If you've been living in a cave your entire life, I'll briefly describe this product. It's a box with a pouch of powder, and a second pouch of chocolate syrup inside. You mix the powder with a measured amount of water, vegetable oil, and eggs; pour it into a pan; throw it in the oven and bake until done. The result: a pan of brownies.

So what ergonomic issues could I be talking about? Well, the box has the instructions on the back. The instructions include the amounts of the ingredients you need to add to the mix, the temperature of the oven and the baking time.

That's pretty important information. In particular, the amount of water and oil you need to add is a particularly important piece of information, I'd guess.

So why the hell is that information in the smallest font on the box?! The font showing that you need to use ½ cup of oil is positively miniscule. So small that it's actually hard to tell whether it says ½ or ⅓ cup. Hell, it may even be hard to see the difference in your browser on this page, depending on your setup.

So, what? Could they not spare the extra few micrograms of ink?!

Wednesday, November 4, 2009


So I just saw a clip from the new disaster movie 2012.

There's a certain give and take that an author and his audience have. The name for it is Suspension of Disbelief. We can watch Roxanne and set aside whether it's plausible or not that someone with a disfiguring birth defect on his face could not get it repaired because of an allergy to anesthetics. Some folks can even watch Star Trek movies without theorizing about how the warp engines work.

But I'm sorry: if you're in a small twin-engine aircraft over the city of Los Angeles while it's undergoing a catastrophic apocalypse, wouldn't the first thing that comes to mind be to perhaps attempt to gain some altitude so that you don't have to navigate between the buildings that are toppling over?

Tuesday, November 3, 2009

Any damn time now, AT&T

Ok, AT&T, it's been more than a month since field trials have started for the AT&T microcell 3G. How long does it really take? You're running out of 2009. Now, while Verizon is hammering AT&T directly about poor 3G coverage, would be an excellent time to roll out a solution to the problem (even if it's a stopgap one).

By the way, this is how stupid AT&T is: the prime market for the microcell is likely iPhone owners. The Microcell web site? A giant flash page. Which doesn't work on the iPhone. Brilliant!

Sunday, November 1, 2009

Stupid Android ad

Let's look at the new Android ad one line item at a time:

iDon't have a real keyboard.

Um... That's the whole point - it doesn't waste the real estate for a keyboard when most of the time you don't need it. Those few occasions where it's necessary to type in text, you can have a portrait or landscape one - your choice.

iDon't run simultaneous apps.

I'll admit - it would be nice to be able to stream XM in the background, but that's the only thing I can actually think of that I'd want to multi-task on my phone. The notifications take care of everything else that I might want to have in terms of background processing, without completely trashing my battery.

iDon't take 5-megapixel pictures.

iDo take 3 megapixel pictures, which is more than adequate for most folks. Besides, if you're taking video, then that's irrelevant.

iDon't customize.

What does that even mean? You can choose from a huge variety of 3rd party cases, accessories... you can rearrange the home screen.... not to mention adding the widest variety of 3rd party software you can get on any mobile device...

iDon't run widgets.

You'd rather run "widgets" (what the hell are those, anyway), than real Objective C applications?!

iDon't allow open development.

That's disingenuous.

1. The developer tools for the iPhone are free.

2. Developers can upload their own apps to their own phone. This means that there can indeed be open source iPhone apps that people could download and install themselves, if they wanted.

3. Anyone is free to give away damn near any app they want.

iDon't take pictures in the dark.

And since I'm not hunting ghosts, that doesn't really bother me any.

iDon't have interchangeable batteries

Which means it's smaller and lighter for the same abilities, since the case doesn't have to support latches and friction-fit battery terminals. Besides, in all the time I've owned cellular phones, I've never replaced the batteries in a phone. Usually, I've replaced the phone first.

Magic Mouse review

I've been saying for a while now that Apple needed to do something to bring multi-touch to its desktop lineup. Well, now they have. I bought a couple of Magic Mice - one for the mac mini in the living room and one for Scarlet's desktop machine. It works more or less exactly like it's depicted on its website. The scrolling with momentum is particularly welcome. It's a great way to scroll through big web pages and documents quickly. I actually hope that they add that feature to the multitouch laptops as well.

The two finger swipe gesture works with Safari as a "back" and "forward" nav action. I didn't think that would be useful at first, but I've actually found myself using it a few times.

The one gesture that's missing is a pinch gesture to zoom in and out (the pinch in Safari makes the text size larger or smaller). A close second best is the control-scroll gesture to magnify the screen. That works really well for the mac mini in the living room as a nice compromise - 720p is too low in resolution, but 1080p makes the fonts generally too small.

If I have one complaint, it's the packaging. They used tape to secure the mouse inside its box, but that tape doesn't come cleanly off - it leaves a nasty, sticky residue behind, and that residue was keeping the mouse from moving smoothly on a mouse pad. I had to break out the Goo Gone to get rid of it.

Saturday, October 31, 2009

Wednesday, October 28, 2009

DVB-S on the spectrum analyzer

Here's what DVB-S looks like on a spectrum analyzer:

This is with the modulator configured for a 4500 kilobaud signal, which results in a 6 MHz wide channel. With a FEC rate of 3/4, that's about 6 MB/sec or so of available MPEG bandwidth.

Compared to 8VSB, the envelope isn't quite so square - it rounds off a bit on either end. And, of course, there is no pilot at the bottom end like with 8VSB.

This is another SA view - this time it's calculating the channel average power and the adjacent channel power. Taking into account the 20 dB attenuator on the input of the SA, it's seeing a channel average power of about 4 watts, and the adjacent channels are 30 dB down from there.

N6QQQ/R bench test results

The receiver and my uplink DVB-S modulator have arrived from Germany. With the DEMI 2330PATV, I'm able to get about 4 watts of DVB-S power output. When I started bench testing the repeater, however, it turned out that even with the amp's bias turned off, the DVB-S exciter alone was enough to be received by the receiver. Not too much of a surprise, given that the exciter and receiver were about 3 feet apart in the garage.

I made a YouTube video showing a complete round-trip - from my analog camera, through the MPEG encoder, modulated with DVB-S, amplified to 4 watts and transmitted with my 23 cm 14 dBd loop Yagi. Then received on the DVB-S receiver, modulated as 8VSB on 33 cm, amplified to about 15 watts, then attenuated by 20 dB and run through a rubber duck antenna. Then received on the loop Yagi on the roof, downconverted from there to TV channel 3, and then received on my portable ATSC TV.


The next step will be to start separating the up/downlink station and the repeater further and further apart. Hopefully, the last test will be with the repeater at its new home on the hill!

The next big demo will be at the K6BEN ATV luncheon on November 23rd. I'll schlep all of the gear for both the repeater and my uplink station over to Harry's Hofbrau and we'll try a full round-trip across the parking lot.

Monday, October 26, 2009

Trivia: four-corner counties

There is only one place in the U.S. where four states meet.

But what about counties?

In California, there are two such spots. The two sets of four counties in question are:

1. San Luis Obispo, Monterey, Kern and Kings


2. Santa Clara, Alameda, San Joaquin and Stanislaus.

There are a couple more that might appear to qualify, but if you look at them closely on a map, they don't quite meet up (merely instead forming two nearby spots where 3 counties meet). For it to truly be a four-corners meeting, two map lines must cross each other cleanly (not necessarily at 90 degree angles, as they do at Arizona, Utah, New Mexico and Colorado). While it is possible to make a map where more than 4 areas come together to meet at a point, there are no "5 (or more) corner" spots in California.

So, there you go.

NFL: feast and famine

So what's happened to football? Week 7 just went by (yes, there's one more game tonight, but I don't think it will have any impact on my point) and there are still 3 undefeated teams! The Broncos, Colts and... The Saints?! And to go along with that, there are still two oh-fer teams: the Rams, and... the Bucaneers?! The Lions managed to win one, so this ends motor city's dream of a repeat.

But when the standings just shy of half way through show such disparity between the top and bottom, something about the competitive balance isn't tuned quite right. This isn't supposed to be Pop-Warner, and people shouldn't seriously ask whether or not a mercy rule is appropriate for the NFL.

Why didn't they schedule a Lions-Raiders game? I'd have loved to be a fly on the wall of the CBS sports scheduling meeting to hear them argue about who would have to go cover that game. Bonus points if it would have been in December and in Oakland (meaningless, cold, outdoors, maybe 10,000 really scary Raiders fans in attendance, unquestioningly blacked-out... What a hoot!)

PLL design

The North Country Radio downconverter kit arrived today. It's a bit daunting, but they did supply some suggestions on how to tap off the RF sample for the PLL and put in the VCO control voltage. That was nice of them.

It's hard to find PLL components anywhere - certainly there aren't any one stop shops anymore. Makes me wonder how companies prototype stuff like this in this day and age.

Jameco still sells the MC145151 in DIP packaging, which is convenient.

The North Country Radio downconverter schematic says that the VCO control voltage is 2 to 8 volts. That exceeds the 5 volts that run the MC145151 PLL, which means that the PLL loop filter will need to be an active one. Given that the reference frequency in this case is 15,625 Hz, the op amp for the active loop filter isn't going to have a lot asked of it - an LM741 would do just fine.

That just leaves a divide by 64 prescaler. That, it turned out, was hard to find, and impossible in DIP packaging. I wound up buying a µPB1507GV from Mouser, but I will need to solder it down to an SSOP-8 to DIP adapter board for prototyping.

The nice thing about working on PLLs is that only on the input side of the prescaler are you dealing with real RF - the entire rest of the circuit is dealing with low enough frequencies that it can all be breadboarded.

Sunday, October 18, 2009

More PLL design

So the design at the moment for the downconverter looks like it'll use the MC145151 PLL and the SA620 LNA/Mixer/VCO. At first, I figured I'd use the MC12080 divide-by-80 prescaler. With a 12.8 MHz crystal and a divide by 1024 reference divisor, that's a channelization of 1 MHz. And that's fine for an ATV downconverter.

But what if we altered the design a bit to take advantage of the fractional capabilities of the a dual modulus PLL chip, like the MC145152?

If we used that same 12.8 MHz crystal and divide by 512, we'd have a 25 kHz reference frequency. With a divide-by-64/65 prescaler (like the MC12054A), we'd be able to achieve the same result, but with a 25 kHz channel step.

A PLL that can drive a dual modulus prescaler has two counters. One of them is the actual output into the phase comparator, the other causes a digital output to change state during each count cycle. That signal changes the prescaler from a divide by P+1 to a divide by P.

Let's say that we set the main counter value to N and the prescaler change counter to A and the lower of the two prescaler values to P. What we'd then wind up with is dividing the VCO output by P*N+A. If the reference frequency is R, then the output frequency will be R*(PN+A). So for 848 MHz, if P is 64, and R is 25 kHz, N would be set to 530 and A to 0. Set A to 1 and the output would instead be 848.025 MHz. For 849 MHz (which puts 909-915 down to TV channel 3), you set N to 530 and A to 40.

In general, for a desired frequency F, you set the N to the integral quotient of (F/R) divided by P. You then set A to (F/R) mod P. Stated another way, you're building a fraction of N + A/P, which winds up being equal to F/(P*R).

Of course, this does mean that the design will need more DIP switches. The MC145152 has 6 bits for the A value and 10 bits for the N value. That's two banks of 8 switches. You could fix the top 4 bits of N to 1000 - limiting N from 512 to 575. The resulting frequency range would be 819.2 MHz to 921.6 MHz - more than enough for our purposes. That's a total of 12 switches - two banks of 6.

So a 12.8 MHz crystal, an MC145152 PLL, and an MC12054A prescaler and an SA620 LNA/VCO/Mixer.

Now the big problem is either finding inventory on these parts somewhere or finding equivalents.

Make your own NFL doubleheader!

I'm watching the Giants and Saints game right now. It's on KCBA. Yay!

KTVU's scheduled to air the Cardinals-Seahawks game at 1. Last I heard, the Raiders hadn't sold out, so that game may not air. That would be our punishment, I guess, for not buying tickets to see JaMarcus throw picks and incompletes. Frank Caliendo said it best today - he called the Raiders "Clippers bad." Word.

Anyway, CBS's game today is Ravens-Vikings. So I am flipping back and forth between two games featuring teams off to a 5-0 start. Can't complain much about that! If KTVU indeed airs the Seahawks game this afternoon, well, I'll have gotten to see 3 games instead of 2. And thus, the antenna gambit pays off!

Saturday, October 17, 2009

K6BEN retransmitted digitally

Today I retransmitted the output of the K6BEN repeater digitally over ATSC.

As soon as N6QQQ/R goes live, I'll start doing this on Wednesday evenings just to sort of bootstrap the use of the new repeater - that way folks will have more to look at on it than just my garage.

It's a miracle!

Look! It's Michael Jackson risen from the dead!

Friday, October 16, 2009

Designing a downconverter

I've done some looking into it, and it appears that the three parts that would be the most useful would be the SA620 LNA, VCO and mixer, an MC145151-2 DIP switch controlled PLL, and an MC12080 UHF prescaler. From what I can tell, those three parts should be able to work together to downconvert from just about any frequency in the 33 cm band down to VHF channel 3 or 4.

Yeah, I know. In the last post, I made an argument for putting it in UHF instead. But the coax losses are much, much lower at VHF, so if it's reasonable or easy to make it happen, well, why not?

The big problem is, so far as I can tell, the SA620 and MC12080 are only available as surface mount devices. It'd be nice if they were available in DIP packaging. But, alas, no. SparkFun electronics, however, sells SOIC-8 and SSOP-20 to DIP adapter boards.

The concept is that the RF comes in and the LNA built-in to the 620 amplifies it a little and feeds it into the mixer. Meanwhile, the VCO generates the IF of about 850 MHz or thereabouts. A little of the VCO's output is fed through the prescaler, and then out to the PLL. The PLL then generates corrections for the VCO's voltage.

Those 3 chips total are less than $15, from what I can tell, from a combination of DigiKey and Jameco.

And that's all there is to it: 3 chips, a 5 volt regulator, 2 sets of DIP switches and some discrete components to tie it all together. For extra credit, it would be fairly simple to add a bias-T to the output to supply power to the thing to mast-mount it. And if it's going to be mast-mounted, then DIP switches are a completely reasonable way to set the LO frequency, since it'll be something you only set once.

In fact, if you're using a computer peripheral tuner, like the HDHomerun, you'll likely just set it for an LO frequency of 848 MHz - that would put 902 MHz at 54 MHz. You'd then just tell your tuner exactly what frequency it should use. The only reason for making the PLL as adjustable as it is is because TV sets aren't agile enough to hunt around other than on normal TV channels. The HDHomeRun, however, can easily be told to look for 8VSB on a channel center of 64 MHz - which is where the 909-915 MHz ATV channel would be found.

Thursday, October 15, 2009

Final repeater pieces ordered

All the pieces are coming together.

The repeater will consist of

From SR Systems:

1 DVB-S 23cm receiver board
1 ATSC 33cm minimod

From Downeast Microwave:

1 3370PAHS amplifier

From Ham Radio Outlet:

1 Diamond X6000A 2M/70cm/23cm vertical antenna
1 Comet KP-20 33cm vertical antenna

I'm going to also set up an uplink station for myself. I want to use it at least at first to retransmit the output from the K6BEN repeater. It will consist of

From SR Systems:

1 MPEG encoder board
1 DVB-S 23cm minimod

From Downeast Microwave:

1 2330PATV amplifier

From PC Electronics:

1 TVC-4S 70cm downconverter
1 RCV3 channel 3 NTSC demodulator

The concept here is that we receive standard 70 cm AM TV on the TVC-4S channel 1 down to baseband video and audio. Send that into the MPEG encoder and transmit it as DVB-S on 23cm up to the repeater. The repeater will then retransmit the transport stream over ATSC on 33cm.

I'll receive that with my receive station:

From PC Electronics:

1 TVC-9S 33cm downconverter
1 HDHomeRun ATSC tuner

I'm not sure I can configure the DVB-S modulator to key on and off based on whether or not there's good video going into the MPEG encoder. If it is, then I could make the whole thing automatic. But if my experience with the ATSC modulator is any guide, it won't do that, so I'll have to turn the thing on and off myself. But Stefan assures me that the repeater (the DVB-S NIM and minimod combination) can key on and off automatically based on the receive signal.

Sunday, October 11, 2009

Michael Moore and Me

From what we have been told, Gizmo's toilet flushing antics make a brief appearance in Michael Moore's latest film, Capitalism: A Love Story.

Gizmo has been on TV a lot. But at least so far as I am aware, he has never appeared on TV without someone from the TV show calling and asking permission. And we've never said "no" to anyone (we did tell the staff of The Tonight Show when they called to ask if he could appear live with a toilet on stage that we didn't think it was likely that he'd make a good appearance, since he wasn't trained to flush the toilet or anything, but we didn't outright say "no" to them). The most we've ever asked was to be told where we can tune in to tape a copy of the clip for our own collection.

So the news that Gizmo makes an appearance in Michael Moore's movie was a complete surprise. They didn't call and ask. We would have said "yes" to Michael had he had the good grace to call and ask for permission to use our video in his film. I don't agree with Michael's politics, but I would have been tickled to see Gizmo on the silver screen.

Given everything I know about Michael Moore, I'm not at all surprised. He wants what he wants, regardless of whatever rules (like Copyright law) he has to trample or people he has to hurt in the process. If you look up "asshole" in the dictionary, there's a picture of Michael Moore.

Mike, you owe me an apology. My only solace is that I know that I'm at the end of a very, very, very long line.

Maybe it's you, Al

Over the course of the last, oh, 30 years of near constant suck, the Raiders have had countless coaches (head and assistant) come and go, and moved twice.

Through all of it, the two constants have been Al Davis, and the aforementioned sucktitiude.

The problem is, you can't fire an owner.

Well, the league some years ago did take extraordinary action against Eddie DeBartolo, Jr., but that was after he was convicted in a corruption scandal. Even then, all the league did was suspend him from an active ownership role for a year.

But the prospect of anyone being able to force Al Davis to hand over the team to someone who can simply do a better job is dim.

But they've tried damn near everything else.

Saturday, October 10, 2009

Downconverters for receiving

The PC Electronics TVC-9S is a very nice downconverter, and I'm glad I bought one, but it is a bit expensive. To really make it easy to get started, I think it would be great if something simpler were available.

North Country Radio make a VCO controlled 33 cm downconverter. I haven't tried it, though, and my one worry is that without a frequency counter, it might be tough to tune. It depends on how much tuning slop your ATSC tuner will allow. But on the other hand, their downconverter is a third the price of the PC Electronics one.

One thing I think that could be changed is that these downconverters are designed to shift 33 cm down to VHF low. That means their mix frequency must be very high - in the 800 MHz or so range.

For DTV, I don't think it's necessary to chose such a low IF. If you picked a mix frequency of, say, 421 MHz, you'd wind up with 909 MHz being output on TV channel 17. That would be ideal for around here, because channels 15 through 18 are unused (since 16 and 17 are used for land-mobile in San Francisco).

So, dear readers, if you can design a cheap crystalized or PLL controlled downconverter to go from the middle of 33 cm to the lower end of the UHF TV band, please let me know - I think you could make a lot of hams very happy.

We have a site!

I've negotiated a lease with a land owner in the East San Jose foothills, so as soon as I can get the last of the equipment, North America's first 100% digital ATV repeater will be on the air!

I've set up a a web site for it, with all of the information on what it will take to transmit in and receive from it.

Tuesday, October 6, 2009

JaMarcus Russell

That deaf, dumb and blind kid sure throws a mean football.

Seriously, I'm a Chargers fan and Russell embarrasses me.

Monday, October 5, 2009

Really, Google?

I got to the CalTrain station this morning in time to catch the 7:25 train so that I could get into work a little early. At 7:27, the signs suddenly said that the train was delayed 12 minutes. I thought the prospects for making up that time in route and still catching the 8 AM shuttle bus were dim, so I decided to check Google Maps on the phone to see what traffic conditions were like.

So Google pissed on my back and told me it was raining.

Here's a great example of what I'm talking about. Here's what Google said at one particular point in the trip:

And here's actually what was going on at the time:

Maybe it's just me, but I wouldn't equate a "green" traffic status with 10 mi/hr.

Thanks for nothing, big G.

Saturday, October 3, 2009

Low bitrate MPEG2

I've been using 5 MB/sec for my experimental transmissions, but I have been hearing from Stefan that European hams have had success with 2 MHz wide 2 MB/sec DVB-S. So on a whim, I set my ATSC transmitter to transmit 2 MB/sec MPEG2 video. And the resulting video looked just fine to my eyes. It got a little blocky when I panned the camera around, so with high motion subject matter, it's not enough. But it's clearly enough for the average QSO.

I still think the receivers should be configured for as much bandwidth as the bandplans will allow (6 MHz on 23cm and 4 MHz on 70cm). If for no other reason than it's conceivable that HD pictures could be sent with H.264 inside 6 MB/sec, and someone might want to try that (despite the fact that it won't be compatible with ordinary TVs).

Friday, October 2, 2009

Diamond X6000A

Wow, the X6000A is big! Yeah, the specs say it's 10 feet long, but it just doesn't really come home until you put it together, I guess. It's a couple feet longer than the Comet KP-20, even. And it has much, much longer radials (likely because they have to work on 2 meters).

One of the issues will wind up being how to mount the two antennas. Of course, most of that depends on the site. But despite the cross-band nature of the repeater, it's still going to be desirable to keep the transmit and receive antennas away from each other - either at different elevations on a tower, or 10-20 feet away from each other horizontally. That will obviate the need to set up a 33 cm band-reject filter to protect the receivers.

Operational differences

Users of K6BEN/R will have gotten used to how that repeater works - in particular, the use of 2 meter audio for coordination. I used to think it odd that the audio wasn't carried into the repeater as part of the uplink, but having used the repeater, it's clear that it's a fairly useful way to set things up. Someone other than the station sending video can be the source for te audio.

The first iteration of the D-ATV repeater won't have this ability: it will simply retransmit the MPEG TS uplinked by the user station. This means that coordination will have to take place via a traditional 2m or 70cm repeater. One thing that is planned for the future, though, is a shack camera going into an MPEG encoder. But that still would mean it would be a different stream than the one the user is transmitting. So you could watch yourself on TV, or listen to the 2m audio and watch the shack cam, but not both (unless you either decode both at the same time with a computer or multiple TVs).

On the plus side, however, the audio that's part of the MPEG encoding will be vastly higher quality than the narrowband FM we're used to. That may be useful in the context of events. Certainly, the ability to multiplex multiple programs and (when multiple receivers come), uplink multiple simultaneous streams will be very useful for events.

Monday, September 28, 2009

"Curing" cancer

I ran across a YouTube video of Lewis Black calling for more research into curing cancer.

Let's look into this a little bit.

Everybody's going to die of something someday.

According to this page Google found me, vascular disease (combining the cerebrovascular and coronary categories) accounted for almost 31% of deaths in 2006 in the US. Cancer caused 23%.

But when you talk to people about what they really mean by "finding a cure for cancer," what they really are talking about are the cancers that cut young lives short unexpectedly.

According to this page, cancer deaths in those under 54 years of age accounted for less than 15% of the total deaths due to cancer. Between 55 and 64, a further 17.5%. More than 2/3rds of cancer deaths are people over the age of 65.

The number of people who die of cancer every year under age 65 is about the same as the number of people who die every year from accidents - and accidents, unlike cancer, are a cause of death that is heavily biased towards the youth and away from the elderly. Should we not spend at least as much time, effort, energy and money stumping for accident prevention if we want to reduce the rate of untimely death?

Besides, we do have cures for cancer right now - early detection, genetic screening, surgery, chemotherapy, radiation therapy - all of these things have given people diagnosed with cancer far, far more hope than they ever have had in the past. And to be sure, incremental gains can be made going forward. And that's not to mention the reduced risk of cancer afforded to those who make healthy lifestyle choices in the first place.

But it's not like deciding we're going to spend X amount of dollars and launch a mission to the moon - and once we land, it's "mission accomplished." It's not like there's something that the scientists have just plain missed that's going to make cancer stop killing people. But that's the case for cardiovascular disease, and dementia, and everything else that kills us too.

Sunday, September 27, 2009

Open colector output

Perhaps it's obvious to most electronics experts reading this, but I thought I'd pass along something I learned today.

As you all know, I'm trying to build a digital ATV repeater. One of the things I needed was a system to key the amp on and off so that it doesn't have to stay biased 24/7 (a waste of power, unnecessary heat and shortens the amp's service life). Fortunately, the amp has a short-to-ground PTT line.

Well, it turns out that the modulator has a TTL "PTT" pin on one of its headers. How do you turn this into a short-to-ground output?

The answer is open collector. I installed an RCA jack in the chassis and simply dead-bug soldered an NPN transistor to the jack, emitter to shell (and ground) and collector to center. I then soldered a 10K resistor to the base, and the other end to a wire to a "pin clip" to clip on to the PTT pin.

And it works perfectly! When I use the menu item to take the transmitter from stand-by to on-air, it keys the amp! Yay!

Football blackout rules?

I guess I don't understand the NFL's blackout rules. CBS has the doubleheader this week, and we will get 3 games here in the bay area - meaning CBS will put on a competing game against the 9ers @ Vikings.

Well, I thought that KPIX wasn't allowed to compete with the home team's away games. Is that not the case?

Meanwhile, I can't wait for Fox to get the doubleheader. Perhaps then I'll get to test out the KCBA extra game theory.

Update: Well, the schedule on the TV was wrong. We didn't get the 2nd game. Instead, we got an infomercial. :(

Next week will be the first big test. Fox has the doubleheader and the morning game on KPIX will be Radiers & Texans. If I am right, that means that there will be no competing game on KTVU, but there will be one on KCBA.

Thursday, September 24, 2009

Gearing up

Next month, I'm going to order a DVB-S modulator (for me) and a DVB-S receiver for the repeater.

Stefan (from SR Systems) says that you can set up a repeater simply by connecting the receiver directly up to the modulator. The modulator will turn on automatically when the receiver detects good reception. Not only that, but it has a "PTT" logic indicator pin that can turn into an open collector output with one transistor and one resistor to key the amp!

After that's done, the MPEG encoder board will be paired with the new DVB-S transmitter board as my user station.

The bad news is that they don't make a DVB-S receiver for 70 cm. Too bad. We'll have to receive on 1.2 GHz. But, of course, we'll be able to do so in a 2 MHz wide channel so we should not have the same interference problems we do with FM TV on K6BEN/R.

All I need besides that is a 15A power supply for the whole thing, a 23 cm antenna, some coax.... and a place to put it all.

For the receive antenna, I'm looking at the Diamond F1230A. It has 13.8 dBi gain. With about 3 dB of coax loss and 9 dB of loss for operating on 1.2 GHz, you should be able to use the PC Electronics ATV DX chart as it is - without having to correct for being on 1.2 GHz. Just assume that the receive site has unity gain. So, for example, if you can generate 5 watts into a Directive Systems 14 element loop Yagi, you'd be able to hit the system from about 15 miles away.

Tuesday, September 22, 2009

Digital amateur TV for the rest of us

I've been concentrating on the ATSC repeater output all this time and have neglected considering the user uplink side of the equation. In a single e-mail with the SR Systems folks, I think I see the way forward.

NARCC, the local repeater coordination body here in Northern California, has not been friendly to ATV in the 70 cm band. And you can't really blame them - it's 6 MHz of real estate that is sorely needed for other things. The big problem is that generating power at 70 cm is vastly less expensive and easier than for the higher bands. Given that state of affairs, it would be very, very nice to be able to use 70 cm as a user uplink band for a DATV repeater.

Well, it turns out that according to Stefan, the europeans have had great success with DVB-S in a 2 MHz wide bandwidth at about 2 mbps encoding! That's excellent news! I'd be shocked if we couldn't find a 2 MHz channel somewhere between 420 and 440 MHz for this.

Not only that, but the DVB-S encoder board is less than half the price of an ATSC one. That means that a user station can be had for €590. Add to that the cost of a Downeast Microwave 7025PACK and you're on the air with about 8 watts of transmitter power for just over $1000! That's not bad for digital ATV!

Friday, September 4, 2009

CalTrain: cellphone boosters, please!

I have trouble with the iPhone under two circumstances: At home and on CalTrain. Our house is made of stucco, which is a giant faraday cage. The workaround has been to install a cell booster. CalTrain is a giant metal box going 79 mi/hr - a worst case scenario for any cell phone on any carrier.

Now, I know that CalTrain just announced service reductions and parking fee increases, so maybe it's not totally apropos to talk about improving things, at least not "in this economy" (how many times in one day do you hear that phrase?). But still... They could add a two band repeater to the luggage cars as a test.

According to Wikipedia, CalTrain was considering adding WiFi service back in 2006. The problem with WiFi is that it doesn't help anyone make phone calls, and it's more expensive, since it means that CalTrain has to obtain mobile Internet access itself somehow.

A cellular repeater in a train car isn't the same thing as microcells in airplanes. There, the signal is back-hauled over satellite links since cellular phones are actually not licensed for use in the air (their widespread visibility to multiple cell sites causes interference).

Thursday, September 3, 2009

Java and the Impossible Generic List

Since Java 1.5, I've been used to writing List<Class>, allowing the compiler to insure type safety of collections.

There's one issue with this, however.

let's say you have an interface. We'll call it TheInterface.

Java is more than content with allowing you to say List<TheInterface>

So what?

The problem with that syntax is that it says that the contents of the List will always be items whose exact type is TheInterface.

But it's an interface. So there will never be any of those.

Stupid Java.

The solution is simple: you're supposed to say List<? extends TheInterface>. This lets the list contain any objects that implement the given interface, which is almost assuredly exactly what you want.

So why isn't List<TheInterface> a compile error?


Wednesday, September 2, 2009

I hate it when this happens

I hate it when you have something fairly simple to do, that can be done a hundred different ways, but every goddamn one fails for some simple reason. Case in point: I have set up my laptop to act as an alarm clock. It opens up the XM Radio online streaming from a cron job.

I have an html file that does the right thing. It has some javascript that performs the "login" step, and then opens the player gizmo inside of an iframe. It works perfectly.

Well, it did. Snow Leopard seems to have broken XM streaming in Safari.

Ok. How about Firefox? XM streaming works fine there, and if I open up a firefox window and type in the file: URL, it works.

But the problem is that Firefox isn't scriptable! There appears to be no way at all, from a shell script, to open up a firefox window onto a URL of your choosing.

What about Camino? It's scriptable, and uses Gecko.... But alas, XM streaming doesn't work there, either - but for a different reason than Safari (looks to me like a cookie issue, but I can't be sure).

So I'm fucked. And by my count, it took the failure of 5 different vendors to get us here. Outstanding.

The return of Channel 1

Some people wonder what happened to TV channel 1 here in North America.

Well, TV broadcasting actually began before World War II, but with the outbreak of war, it was suspended. In 1945, when the war was over, the bands for both TV and FM were realigned (much to the detriment of Edwin Armstrong's fledgling FM radio network - all of the FM receivers sold before that time were instantly obsolete). Channel 1 was from 44-50 MHz, and channel's 2 through 6 were as they are now.

That had the rather uncomfortable distinction of sandwiching the amateur 6 meter band right between two TV broadcast channels. Fortunately for us hams, channel 1 was reallocated to land mobile services. Since by that time people had already bought a nontrivial number of TVs, the channel numbers were not changed, and so to this day, channel 2 is the bottom of the TV band at 54-60 MHz.

Spring forward to today. KAXT switched on their ATSC transmitter a few weeks ago, putting out 12 streams of video and 3 of audio on virtual channel 22 (RF channel 42). This collided with KRCB, which was also using virtual channel 22 (via RF channel 23). Back in the days of analog broadcasting, the two used to collide with each other, since they were both on channel 22. The net result was to deny those of us here in the South Bay any chance at all of receiving KRCB, even though with a good enough antenna we had a good shot at it.

Well, the long and short of it is that virtual channel number "collisions" between broadcasters are undesirable. Some receivers get very confused when there are multiple 22-1 streams. Some prefer the most recently tuned one, some allow two to exist... It's very messy.

Well, KAXT has asked the FCC to change their virtual channel number to 1. The FCC more or less said, "well, if that'll fix it, sure." The PSIP TVCT spec does allow for a channel 1. It'll be interesting to see how many tuners balk at it, though.

It'll be interesting to see what KTVJ decides to do. In theory they have three choices of virtual channel - 4, 20 and 36 - all of which are already in use.

My suggestion? They should pick 37. It's one up from 36, which is their current branding identity (which they can't use since it's taken by KICU), and TV channel 37 has traditionally been unallocated because it is actually a radio astronomy quiet channel (there's some interesting physics that manifests itself at or near 49 cm).

Friday, August 28, 2009

ATSC Haiku

Blue screen vanishes
blue sky and green fields appear
call sign, blue screen returns

6 dB ratio
from peak to channel average
power costs a lot

no snow, no ghosting
perfect signal every time
except for drop-outs

Ricochet bankrupt
phoenix is reborn from ash
on 33 cm

MPEG2 for sound
AC-3 costs too damn much
stupid patent trolls

ATV serving all of
silicon valley

Thursday, August 27, 2009

ATSC power conundrum solved?

I've learned a bit more about some of the features of the HP 8590L spectrum analyzer I got off eBay a while ago. One feature it has is the ability to calculate channel average power and the adjacent channel power ratio (that is, how many dB down the power is on the 6 MHz above and below the channel of interest). And at the preferred settings of the exciter, the output power is about 15 watts, with the adjacent channels being down about 35 dB. That's a little more out-of-channel garbage than I had hoped for - a bit more than 20 mW of ERP. But even so, on 900 MHz that small amount of power should die easily within half a mile of the site. Heck, I've transmitted with the bare exciter at approximately that power level and been unable to receive it half a block away from home. So I'm not going to worry about it. As always, reducing power will reduce the reconstituted sidebands, though the bare exciter has sidebands that are only about 48 dB down from the main signal, so there's only so much more improvement to be had.

Another bit of good news is that I spent some time "boiling the dummy load" this evening. Without the muffin fan, the heat sink of the amp gets so hot that you can't comfortably touch it. But with the muffin fan sitting on top and running, the heat sink stays almost as cool as the ambient air temperature (almost). So that bodes really well for the health of the amp when it's put in service.

Monday, August 24, 2009

First words from the moon?

If you ask people what were the first words spoken by a human from the moon's surface, their answer will often be Neil Armstrong's "One small step" quotation. I happened to think about that a bit today, and it doesn't really ring true.

As of yet, no human being has truly been in contact with the lunar surface. The only way such an event would truly be possible would be to build a pressurized enclosure on the moon. Only then could someone walk on the surface without the protection of a space suit. What we're left with is an approximation - the Apollo astronauts who visited the lunar surface did so constantly surrounded by a bubble of Earth's atmosphere, whether that bubble was located around them in a suit while they were EVA or whether that bubble was around them in the LEM. And Neil Armstrong and Buzz Aldrin spent an extended period of time after the actual landing before they opened the hatch and descended to the actual lunar surface. Buzz even had rime to take communion.

So how do you pick the first words spoken from the moon? Well, they'd have to be the first words spoken by a human being who was inside of a vessel that was in contact with the lunar surface. And if you read the NASA transcripts of Apollo 11, you'll find that the first words from the lunar surface given that definition actually came from Buzz Aldrin.

As the LEM was descending for its final landing, a probe descending from one of the landing legs made contact with the lunar surface. That probe lit a light on the instrument panel. When that light lit up, Buzz said, "Contact light," as a cue to Neil to cut the engines and let the LEM fall the rest of the way to the surface.

And those words were the ones that made history.

History is often like that. The first creatures ever to cross the Golden Gate other than by water or air were a pair of workmen on the Golden Gate bridge who were engaging in a repair mission of sorts. They hauled themselves over the unfinished cables and into the history books more than a year before the first pedestrian would cross the finished bridge. The flag raising at Mount Suribachi (on Iwo Jima) that was widely and famously photographed was actually the raising of the second flag, ordered by a commander who thought the first flag was too small. If you visit the Amundsen-Scott South Pole station, you'll find two poles - the real South Pole, which is just a simple spike in the ground and a small, plain sign, and a few hundred yards away, is the so-called "ceremonial" pole, which is a giant barber-pole decorated monstrosity surrounded by the flags of all the nations with a presence in Antarctica. The ceremonial one is the one that people expect to see, but it's not the real one.

Final TX configuration set

I've set up the transmitter in what I believe will be its final configuration. I put a 6 dB attenuator on the output of the exciter to raise the output power setting required so that it would be in the middle of its range rather than on the end. Getting the exciter output to an average power of about 6 dBm now means setting the output power to 10 instead of 3. I traded some mail with the guys at SR-Systems and they said that the "sweet spot" is anywhere between 5 and 13. Anyway, with 6 dBm of power, the amp is supposed to generate 15 watts of power, which means an output ERP of about 75 watts. I put an N to UHF adapter in the input of the spectrum analyzer and then put a big nail in the center conductor socket and laid the coax next to it that was hooked up between the amp and the dummy load. It may be less than perfectly accurate, but my hope is that it's close enough to score. Anyway, with that setup, I could see the "ramps" of out-of-channel noise well enough to check how strong they were relative to the ATSC pilot (which, again, is 11.3 dB down from the channel average power). At a power setting of 10, the skirts were just about 47 dB down from the average power, which is right where the part 73 channel mask would have them. At a power level of 11, they come up to closer to 40 dB down. Now, the part 73 channel mask is not of any particular relevance for part 97 operations, but we amateurs are required to reduce spurious emissions in accordance with good engineering practice. Besides, limiting the output power can't help but make the amplifier just that much happier, which means it is likely to last longer - particularly given that it will be in a repeater shack that is not climate controlled.

I have a 20 watt 20 dB attenuator arriving in the mail tomorrow, so I'll be able to run the output of the amp directly into the SA for a final check tomorrow evening. Not only will I be able to directly measure the out-of-channel emissions, but I'll be able to get an accurate power output reading as well.

So it will put out 75 watts of ERP (perhaps it might drop down to 70 or so with coax losses when all is said and done). That still should be receivable everywhere the analog signal of K6BEN is receivable today.

Get your popcorn ready

So, the 33 cm ATSC transmitter will hopefully be going into more or less full time service sometime soon now.

So just to get people prepared, let me outline what you'll need in order to see the transmissions.

First and foremost, you must have a line-of-sight to the east San Jose foothills. And it has to be a real line of sight. That means that on a clear day you can look in the direction of Mount Hamilton and see the mountains. A single tree in the way will knock your received signal strength down by 20 dB - 100 times!

At the location where you have that nice, clear line of sight towards Mount Hamilton, you'll need to mount a 900 MHz directional antenna. I'm about 10 miles away from where the transmitter is going to be located, and I can receive it with a 7 element 10 dBi 900 MHz Yagi. I bought it off the Internet for about $30. If you're further away, or if you have trees in the way, you'll need something bigger, like the Directive Systems 3318LYARM 18 element 16.5 dBi loop Yagi.

You'll need to use as short a run of coax as possible from the antenna to the downconverter, and the best coax you can afford. Losses at 900 MHz can be severe. I use LMR-400.

The best downconverter I've found can be had from P.C. Electronics. You'll want the TVC-9S 900 MHz PLL controlled downconverter. From there, you can run ordinary 75 ohm cable TV coax from the downconverter to your ATSC tuner or TV. Set the downconverter to channel 2, which maps 910-916 MHz to TV channel 3.

As a bonus, if you have a good clear line of sight to Mt. Diablo and an analog TV, you can try picking up the W6CX analog ATV repeater output on 918-924 MHz.

You'll need to perform a channel scan while the transmitter is active in order to discover the downconverted signal on channel 3. Fortunately, the K6BEN repeater is active from 0 to 10 minutes past each hour transmitting ID slides. So your best bet is to scan at about 2 minutes past the hour. Of course, if your tuner/TV is capable of tuning directly to a channel without scanning, you can simply tune it to channel 3.

Saturday, August 22, 2009

New Amateur ATSC DX record - complete with video

I went up to the Sierra Rd QTH in the east foothills, and this time everything went perfectly. I was able to capture a video from up there, and with a good line of sight and 80 watts of ERP, I was able to get a signal strength of 100 and a signal quality of 75 or so on the HD HomeRun. This location is very similar to the location of the K6BEN repeater and is in, more or less, the same direction. Google Earth says it's 9.07 miles away from home. The coordinates are 37.413081° N, 121.824316° W.

Here's a screenshot from my phone's ssh client showing the status report from the HDHomeRun with the signal strength and qualty (the first line showing no reception was a control - the transmitter was unkeyed):

It was actually sort of tough to get the phone to cooperate. Cell phones operate in the 800 MHz range, and transmitting 85 watts of 900 MHz right next to the phone desensitized the receiver somewhat. I did manage to get working in enough fits and starts to check the signal strength and start and stop the recording, thank goodness.

The receive antenna was a 7 element (10 dBi) Yagi - about $30 off the Internet, and the reception was almost perfect. That pretty much proves that this transmitter is going to work. With a real antenna - like the 18 dBi loop Yagi I have on order - reception should be possible from perhaps 30 miles away with a good line of sight.

Unlike the first time, it was not necessary to adjust the power. The exciter was set to power level "3", which is an average power of about 0 dBm, or a PEP of about 6 dBm. That means an output power of about 16 watts or so, for an ERP of 80 watts. Of course, all of that is in theory. Still on my to-do list is to run this setup through a proper sampling wattmeter and dummy load to get a measured output power level and get a good measurement on how far down the out-of-channel emissions are. Part 73 contains an emissions mask requirement that says that the out-of-channel emissions must be reduced from the channel average power by at least 47 dB - that is, 36 dB below the pilot. That's a pretty reasonable goal to shoot for. At the power we're contemplating, it'd be less than a couple milliwatts. At 900 MHz, that ought not to be a problem.

Tuesday, August 18, 2009

A major amateur ATSC milestone achieved

I just got back from a "DXpedition" of sorts. I went to the crest of a hill in Cupertino and transmitted ATSC at 910-916 MHz and successfully received a picture at home.

The path length, according to Google Earth, is 6.59 miles. I now claim that as the amateur ATSC DX record. I'll be happy to be proven wrong, but so far as I know, nobody apart from a professional broadcaster has transmitted an ATSC signal and successfully received it at that great a distance.

Alas, I don't have any recordings. In order to make this work, I connected the TVC-9S to the best tuner in the house - our brand new Samsung 52" LCD TV in the living room. I then drove off into the night and called Scarlet on the cell phone and asked her to watch. The reception wasn't perfect, but it was there for reasonable stretches.

The receive antenna was a 7 element 900 MHz Yagi I bought off the Internet for about $30. I'm still waiting for the 15 element loop Yagi from Directive Systems - that should give me an 8 dB boost in receive gain when it comes. So the total receive gain was on the order of 7.8 dBd, taking a small loss for coax.

On the transmit power side, that's a much grayer area.

Recall the following rules of thumb: If you can see the ATSC pilot on the spectrum analyzer, it's power level is approximately 11 dB lower than the channel average power level. The peak-to-average power ratio for ATSC is about 6 dB. So the pilot to PEP ratio is 17 dB.

I started out with the minimod power set to "3" on a scale of 1 to 15. On the spectrum analyzer, that sets the pilot at about -11 dBm, which means the channel average power is about 0 dBm. Add 6 dB for the peak-to-average ratio, and that's an input PEP of 6 dBm. The power curve of the 3370PAHS has that being an output power of about 47 dBm (50 watts), or an average power of about 12 watts. That's right between the 1 and 2 dB compression points for the amp. That signal didn't quite make it. I had actually made two trips out to the transmit location - the first time was with the HDHomeRun set up as the receiver, and that configuration did generate a signal strength of about 70, but a signal quality of 0. With the TV hooked up, I didn't have ready access to any signal metrics, so it was just whether it would decode at all or not.

In a fit of impatience, however, I decided to crank the power up, just to see. And sure enough, a power setting of "12" was what it took for decent reception.

Now, that's a pilot level of about 0 dBm, or an average input power of 11 dBm, or an input PEP of 17 dBm. The amp's specifications show it is fully saturated at 16 dBm input power, for an output power of 100 watts PEP.

I can't for the life of me imagine that the amp was very happy doing that.

I can't look at the output of the amp on the spectrum analyzer, since it exceeds the maximum input level of 1 watt. I do have a 25 watt 20 dB attenuator on order, however. When it gets here I'll be able to look and figure out exactly how terrible the splatter is from running the exciter that hot. If previous experience on 420 MHz is any guide, it won't be pretty.

What I can't quite wrap my head around, though, is that if the amp is being overdriven, how can it be that that actually improves reception? Surely an amp that's heavily clipping ATSC would make the eyes close up like a punch drunk boxer's.

We'll have to wait and see. In the meantime, I'm happy to claim some small success, and I'd like to publicly thank my lovely wife Scarlet for helping me verify this transmission. I couldn't have done it - or anything thus far - without her unending help, assistance and understanding.

Friday, August 14, 2009

YouTube DIY TV antennas

I was fooling around today and ran across a collection of videos on YouTube talking about making homemade "HD" TV antennas. Just about all of them are 4 bay bowtie dipole arrays. Pretty much a Channel Master 4221 without the screen, but usually built by screwing coat-hanger wire to a 2x4.

That'll work ok, but there are a few caveats that I feel duty bound to point out:

1. Measure carefully. All the measurements are fairly critical on an antenna like this. Particularly the length of the elements and the distance between them.

2. The CM4221 has a reflector screen behind it. This gives the antenna F/B ratio that it otherwise wouldn't have. Particularly around here, this is absolutely necessary to reduce multipath. The 4221HD has a modified screen that acts like a VHF-hi dipole. This allows it to receive channels 7-13 in addition to 14-51.

3. Put two of these next to each other (again, measuring the distance carefully) and connect them together and you'll have an 8 bay - the equivalent to the CM 4228, one of the best UHF antennas out there.

4. If you put this antenna outdoors, you're going to either need to build it far more robustly than most of the videos show, or you'll need to replace it every few years as it corrodes.

5. If you put this antenna up indoors, you're fooling yourself. For such an antenna to exhibit its designed gain, it must be mounted several wavelengths away from other objects. Because of the huge amount of multipath involved, indoor reception is a crapshoot. It always has been. It's just that with analog, it was easier to make do with a worse signal, or to turn a bad one into a good one experimentally (what I like to call "Antenna Twister").

6. Some of these video describe this as an "HD" antenna. Even Channel Master is somewhat guilty of that in adding "HD" to the model numbers of some of their antennas. No. Antennas do not care about the nature of the modulation of the signals they receive. Antennas care about frequency. And TV post-transition is using the same frequencies as it was before (fewer of them, actually, since the top 100 MHz of UHF has been reallocated). So a TV antenna is a TV antenna and always has been. And TV antennas have not significantly changed since the TV bands were fixed after World War II.

Monday, August 10, 2009

Mineta International: Best at what?

San Jose's airport was recently named the airport of the year. Yes, you heard that right. If you've ever had the misfortune to have to use that airport, you may be confused as to how that never ending construction zone, where the roads are never configured the same way twice in a row, could possibly win anything that isn't a boobie prize. If you read the article, the reason becomes obvious: they didn't ask the passengers. They asked the pilots. It's a little like asking the bus drivers' union to name the route of the year.

Mineta International is a fitting tribute to our former congressman: provincial, backwards, and perpetually being reconstructed. Quite honestly, the best reason to stay alive is to see which transportation boondoggle gets finished first: BART to San Jose or the Airport.

Saturday, August 8, 2009

Test result

Since I didn't give much advance notice for this test, I wasn't expecting much response. Really, what I was going to do was to see if I could receive anything with the HDHomeRun being driven by the TV antenna feeding into a TVC-9S downconverter.

Well, from Cañada College, I was unable to even tickle the signal strength meter in the HDHomeRun - it couldn't tell the difference between the transmitter being on or off.

But I didn't give up. I went by a spot I know about in the Cupertino foothills - near Miles' old house (for those of you who know Miles). From there, I set the transmitter up again and this time I was able to bump up the received signal strength by 10 points, and make the signal quality gauge go up from 0 to about 5 at one point.

That's a path length of a little over 6 miles (compared to almost 19 miles for Cañada). A LR analysis of the path between Cañada College and my house compared to the Cupertino hills QTH and my house shows a path loss difference of 12 dB or so. The predicted field strength for the Cupertino hills QTH is 76.7 dBµV/m and for Cañada is 65.21 dBµV/m.

Keep in mind that's with a receive antenna pointed the wrong way by about 45 degrees and tuned to a band almost double the wavelength. In other words, I'm relatively sure I was paying quite a receive penalty with that setup. But I still managed to tickle it.

I have a proper 33 cm loop Yagi antenna on order, but it hasn't arrived yet. When it does, I'm confident that I'll be able to pull in the signal from the Cupertino QTH at least.

Test at 1

I've got to head out for ham tests, but after that I will be at Cañada College at 1 as promised transmitting ATSC at 910-916 MHz with about 150 watts of ERP. If you have a TV antenna and a spectrum analyzer, and you're in the South Bay or Southern Peninsula (South of San Carlos), please hook the two together and see if you can see anything. Thanks in advance, and fingers crossed!

I will be on Charlie (WA6TEM/R: 147.855-, PL 100Hz) monitoring for reports or questions or what not.

Hope someone can see me!

Friday, August 7, 2009

Hall of Vaporware

So, where the hell are these products we were promised?

  • TomTom for iPhone
  • iPhone tethering
  • iPhone multimedia SMS
  • AT&T Femtocell
  • Next generation DirecTiVo
  • And, of course, no such list would be complete without mentioning the Flying Cars

Saturday, August 1, 2009

68 channels and counting!

KAXT-CA lit up their digital transmitter today (or sometime in the last couple days). They're RF channel is 42, taking over the old KTNC analog spot. They join the quad of stations on Mt. Allison. Their analog transmitter over in the East San Jose foothills is still up on channel 22. It's unclear how long it will stay.

But get this: They're transmitting twelve streams! Most of them are foreign language or religious or shopping, so there probably isn't a lot I'll be watching. And, of course, to fit 12 streams in 19 MB/s, they've had to squeeze the hell out of them. But their signal is good and strong.

So welcome to the digital age, KAXT!

There are only a couple stations left to show up. One is KMMC. They're set to flash-cut to digital on channel 40 sometime next month. Another is KTVJ, which will begin transmitting from Mt. Tamalpais on channel 4 sometime next month. Although there is a clear line of sight from here to Mt. Tamalpais, it'll be interesting to see how challenging it is to receive VHF low ATSC from so far away. The electrical noise might wind up drowning them out. Not to mention I'll probably need to build a dipole or perhaps a 2 or 3 element beam to pull them in (did I mention that a dipole for 70 MHz is gonna be almost 10 feet long?).

Friday, July 31, 2009

900 MHz ATSC test, Cañada College, August 8, 1 PM

Well, since the entire goal of all of this experimenting is to set up an ATSC repeater output at 910-916 MHz, it's time to leave 70 cm behind and concentrate on the 900 MHz band. To that end, I'll be schlepping the gear up to the Cañada College location the Saturday after next. I'll be on the air for as long as I can starting at 1 PM on Saturday, August 8.

In order to receive this transmission, you'll need a 900 MHz antenna, a downconverter, and an ATSC receiver. You can get a suitable one from PC Electronics. Order the TVC-9S (use channel 2). Or you can build your own, if you're handy with that sort of thing. For an antenna, you're going to need to build a beam. In my experience with ATSC, having a directional antenna that you can use to reduce the impact of multipath is critical. It's going to be even more so at 900 MHz with all of the part 15 QRM.

The transmitter will be at 37.448773° North, 122.263856° West, and I'll be transmitting with about 150 watts of ERP. Look for me!

Monday, July 27, 2009

On progress

Western Digital is now shipping a 1 TB 2.5" hard disk.


A terabyte is now about the size of a deck of playing cards and can be powered by your laptop's USB port.

In about 1990, I participated in a Usenet (remember that?) "group buy" of 1 GB SCSI hard disks. That disk was a 5.25" "full height" form factor - that is, it fit in the same amount of space as two DVD-ROM drives stacked on top of each other.

It hasn't even been 20 years and now you can fit as much data as 1000 of those drives into about a tenth of the space, having paid about a fifth of the price for the privilege.

Free Joke

Here's a joke you can use on your friend. It requires you to be sort of good at improv, and your friend to be up on Hollywood gossip. It goes something like this:

You: "Man, what happened that all of the Celebrities are all dying at the same time? Karl Malden, Michael Jackson, Billy Mays... And the latest is some Hollywood actress just died after she stabbed herself with a knife!"

Him: "Really? Who was it?"

You: "I read about it this morning. I don't quite remember the name. Her first name started with an R.... Something like 'Reese.'"

Him: "Witherspoon?"

You: "No, no. With a knife."

Ba-dump bump. Thank you. I'll be here all week. Try the waitress and tip the veal.

Friday, July 24, 2009

The great myth of TV and customer service

You know, I'm rather surprised that I've never expressed this thought in my blog. I tried searching, and it hasn't turned up.

An awful lot of how TV works is rather easily explained once you know and understand the hidden truth of TV, at least as it is practiced in the United States today.

People watch TV and feel like they're the focus of the industry. That all that work and all that money spent goes into serving them and their entertainment needs. And that's true, so far as it goes.

But the fundamental, dirty secret truth is that despite that, you're not their customer.

You're the product being sold.

The advertisers are the customers, as far as the TV stations and networks are concerned. They make and transmit TV shows to attract eyeballs. Those eyeballs - our eyeballs - are sold to the advertisers. And that's what makes the world go 'round.

Don't get me wrong - TV stations want to keep you happy. The same way a shepherd wants to keep his flock happy. But they have no incentive to do anything at all that will cost them any money unless it brings more eyeballs, which indirectly brings them more money.

And that's not a bad thing. It's capitalism in action. It surely beats the alternatives on offer elsewhere - government funded broadcasting, where the only connection between the money and the programming is a bunch of government bureaucrats who either have an agenda of their own or - perhaps worse - are insufficiently incentivized to care.

Wednesday, July 22, 2009

Poker of late

So I haven't been playing a lot lately. Here's a good explanation for why not:

Out of the last 20 games I've played, I cashed 6 times, came in fourth 7 times, got 7th or 8th 5 times, one 9th and one 6th.

If just 3 of those 4ths were 3rds, I'd be profitable.

The 18 games before that, I cashed about half the time, got two fourths, 4 7ths, a 6th and 2 9ths - which is the way it normally is when I'm not getting skewered repeatedly. It's the pattern I would expect to see most of the time. The 4 7ths is a bit lumpier than I'd expect, but it is a very small sample size, after all.

To add to that, the last midnight tournament I lost in the first hour on the back of getting pocket kings vs. pocket aces, and the time before that I came in 7th when I needed to come in 5th to cash.

I hate this fucking game.

I wonder what they were really thinking

I don't think I quote or point to other blogs too often.

But I saw this one on EngrishFunny, and just had to share it:

engrish funny dont choking

Now, I can understand the "Toilet for ladies only" part, but what's up with the "Don't choking" warning?!

Friday, July 17, 2009

Walter Cronkite RIP

So help me out here. We lose Walter Cronkite, but we still have Larry King? Really?

YouTube fun!

Check this out. It's not the first time I've seen this sort of thing, but they've done a relatively good job. It's not quite Cookie Masterson material, but I have high hopes that they'll get better over time.

Thursday, July 16, 2009

Amateur Radio license exam prep - The Arithmetic

The amateur radio technician exam is mostly about memorizing rules and facts. As such, the best advice I can give is to go visit the AA9PW practice exam generator page and take the test repeatedly until you stop regularly failing it. It's actually not that hard to guess most of the answers. The ones you can't guess, you can just learn by repetition as you keep taking the practice tests.

There is, however, some math you should learn how to do rather than memorize, as it is easier. The laws of physics that embody the math you need to learn are embodied by 3 basic formulae. They are, E=IR, P=IE, and C=λω

Now, I can see some of your eyes have just glazed over. But bear with me. It's not that hard. Honest.

The first formula is E=IR, which is known as Ohm's Law. It's the relationship between the voltage drop across a load of a given resistance with a given amount of current flowing through it.

E, perversely enough, is the mathematical symbol for voltage. No, it's not V, 'cause that one was taken (Volume). It's E. You'll just have to remember that one. Voltage is electrical potential, more or less. People often compare voltage and current to water running through hoses. Voltage is analogous to the water pressure.

I, again, perversely enough, is the mathematical symbol for current. Electrical current is measured in Amperes, or Amps for short. Current, using the same water analogy, is how much water moves through the hose in a given time.

R is electrical resistance. Resistance is measured in units called Ohms, denoted by the greek letter Ω.

The basic formula is listed as E=I×R, but if you divide both sides of the equation by R, you get I=E÷R. Divide both sides by I and you get R=E÷I. If you think of those divisions as fractions, then you wind up with this little graphic symbol you can use to remember the relationship:

So that circle represents the relationship. If you remove from the circle the unknown you want to solve for, what's left tells you what the rest of the equation will look like. For example, if you remove the I, you're left with E over R, or E÷R. If you remove the E, you're left with I next to R, or I×R.

So, take question T4D04, for example:

What is the resistance of a circuit when a current of 3 amperes flows through a resistor connected to 90 volts?

A. 3 ohms
B. 30 ohms
C. 93 ohms
D. 270 ohms

They want to know R, and they've supplied you with I and E. R=E÷I. In this case, R=90÷3, or 30. The answer is B.

The next formula relates voltage and current to power. Power is P, and is measured in Watts. I and E are current and Voltage, just like before. P=IE. And like before, the circle chart can be used to figure out all of the relationships:

Let's use question T4E06 as an example:

How many amperes are flowing in a circuit when the applied voltage is 120 volts DC and the load is 1200 watts?

A. 20 amperes
B. 10 amperes
C. 120 amperes
D. 5 amperes

They want to know the current (Amperes), and they've given you the power and voltage. I=P÷E. Or, in this case, I=1200÷120: 10. The correct answer is B.

The last one looks a little funnier, but in truth it's actually easier. The formula is C=λω - the speed of light is equal to the frequency of a wave times its wavelength. Well, the speed of light is 300,000,000 meters per second, or 300 million meters per second. Wavelengths are in meters, at least for the purpose of this exam, and frequency is measured in Hertz (abbreviated as Hz). One Hz is one cycle per second. If we divide both sides of the equation by a million, you wind up with the formula 300 = frequency in Mhz × wavelength in meters. We can make a circle chart up for that one too:

In this case, we will never have the 'top' of the chart be an unknown, so we wind up with only two formulas, both of which look the same: You divide 300 by either the frequency in MHz or the wavelength in meters, and you get the other value.

Take question T1C05:

Which amateur band are you using when transmitting on 146.52 MHz?

A. 2 meter band
B. 20 meter band
C. 14 meter band
D. 6 meter band

300÷146.52 is approximately 2. The correct answer is A.

This formula can also be used to figure out antenna lengths. Take question T9A11:

What is the approximate length, in inches, of a quarter-wavelength vertical antenna for 146 MHz?

A. 112 inches
B. 50 inches
C. 19 inches
D. 12 inches

146 MHz is 2 meters. A quarter wavelength is half a meter. Half a meter is about half a yard, or a foot and a half or about 18 inches. The correct answer is C.

And that's it. So far as I know, that's all the math you need to know and understand to pass the technician exam. All the rest of it is just rote memorization of facts and rules.

Good luck!