Sunday, July 12, 2009

Back to D-ATV: 900 MHz amp

It's been a while, but I've decided to try and ready the ATSC transmitter for a possible placement as an additional output on K6BEN/R, at least to start with. I've talked with Ben (W2NYC) about it and he seems receptive.

I tested the DEMI 7730PAHS 70 watt 900 MHz amp. From what I can tell, I'm getting something like 35 watts out of the thing (the ATSC pilot is at about 33.7 dBm. If you measure the pilot, the signal's power level is about 11.8 dB up from that, so 45.5 dBm, which is about 35 watts), which actually is more than I expected, given the ~5 dB peak-to-average ratio of ATSC. That winds up, with the KP-20, being about 150 watts of ERP. That's still way low. By comparison, KFTL-CA transmits from the top of Mt. San Bruno with 15 kW of ERP. It barely cuts in and out here. My proposed signal is 20 dB down from that, and is double the frequency. That doesn't particularly bode well. The only TV station around here that will be doing ATSC with that little power is the proposed operation of KTVJ on Mt. Tamalpais on channel 4 at 300 watts of ERP. But channel 4 is 66-72 MHz - almost 4 octaves lower.

But really, there's nothing I can do but try. It will either work, or it won't.

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