Re: Higher voltage for Bitx40 Final


Just finished building my BitX40 after playing with the circuit for a few weeks. Early tests on mine suggested that using the small booster I have and raising the PA voltage from around 14 to 24 did seem to increase the power by the square of the voltage ratio, so matching these experiences. Admittedly, I was trying to read this on a 450w dummy load meter, and yelling into the mic, s not very accurate. So this past weekend I did get a QRP wattmeter that could read 30w as full scale and get a better idea of how much I am increasing.

However, now when I apply 24v to the final the power output actually drops from 6w to 4w! The only significant cuircuit difference is that I am now running the other 2 power connections (main board and Raduino) through a 7812 regulator, and since it is not getting quite enough to regulate to 12v, it is delivering about 11.5v to those boards, which I assumed was just a bit safer. The voltage booster is not dropping voltage under load, so I am befuddled as to why the power actually drops when I apply the higher voltage. I did recheck the PA bias and raised it up closer to 100ma, but I notice it slowly increases from wherever it is set if I continue to hold the PTT. Any ideas? Perhaps I should short the input to the output of the little 7812 to see if that actually had an effect.


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