Monday, August 24, 2009

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.

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