Monday, November 10, 2008

Overall repeater design

So I am not sure I've gone through in detail all of the parts that have to come together...

To just go up on top of a hill and transmit DTV is one thing, but again, the goal here is a repeater.

Pieces still needed:

The final amplifier. I have a line on a 100W model, which would be a boost compared to the DEMI 70W (which I'll be fortunate to get 40W and still have it be linear). 100W into the KP-20 I have would be half a kilowatt ERP! From Mt. Chual, that would almost certainly blanket the south bay nicely.

But it will need a 28 VDC power supply, and I'll then need a 28-12 volt DC-DC converter (@ 1A) to power the rest of the gear.

I'll be needing to place another order with SR-Systems - this time for a 4:1 TS MUX, another MPEG encoder and a DVB-T receiver for 426-431 MHz.

A 2 meter NBFM receiver for a 2 meter talk-in / control channel

A tower camera

A 1.2 GHz FM TV receiver

A Diamond X-6000 receive antenna and a 3 port duplexer (2m, 70 cm, 23 cm).

And lastly, I will need to build a repeater controller. For this, I'll use an Intuitive Circuits OSD generator, a Javelin Stamp, a DTMF decoder (for control) and a 567 wired as a horizontal sync detector (to detect video input from the FM receiver). I'll use the Javelin's UART class to bit-bang serial output to the OSD, another output pin as a PTT control line (which really will just key the amplifier - the exciter will free-run so as to reduce latency), and two pins as video-good input signals - one from the 567 for the analog video input, and the other from the DVB-T receiver.

The whole thing will probably draw about 600 watts of AC power while transmitting.

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