Saturday, November 15, 2008

Ready for 420

The DEMI 7025PA kit arrived yesterday and I took it to work with me and assembled it after work. I'm really bad at surface mount stuff, but I managed to get the thing together without any undue issues.

I assembled the amp without any changes in bias (they include some extra resistors you can use to reduce the bias voltage if you want), and without the load resistor on the input (to maximize the sensitivity). The amp is unbelievably sensitive in this configuration. Turning the power up past 4 (on a scale of 1 to 15) saturates the amp (that is, starts increasing the out-of-channel skirts without appreciably boosting the amplitude of the main signal). But so far as I can tell, I'm still getting about 10 watts of channel average power, or 20W PEP (remember, the peak-to-average ratio for 8VSB is 3 dB).

Even at minimum power, the out-of-channel skirts are a bit higher than I would like to see, but it's nothing that a mask filter can't fix, if I were going to run on 70 cm a non-trivial percentage of the time.

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