[HomeBrew] Help with QRP Driver/PA

[Steven Weber]

>The problem I have is that the CE stage is not providing any gain on 20m.
>collector current, with a 180 ohm collector resistor and 100 ohm emitter
>resistor. A 100 pF capacitor in parallel with the emitter resistor provide
>some bypassing to increase gain at high frequencies.

Andrew,

Try putting an RF choke in series with the collector resistor. (between the
collector and the load resistor in there now). I'd try about 2 uH to start
as a off the top of the head guess. That value should be low enough not to
get excessive swing at 7 MHz, but increase the swing at 14. 

Also, realise that the gate capacitance of a IRF510 is on the order of 1000
pfd. The 2N3904/3906 push pull driver stage may not have enough current
gain to drive that large a capacitive load at 14 MHz. It maybe instructive
to see what the voltage swing from the P-P driver is with a 10 ohm resistor
( the 1000 p reactance at 14 MHz) as opposed to driving a 1000 p cap. A
2N2222A and 2N2907 pair might be a better driver. 


72,
Steve, KD1JV
"Melt Solder"
White Mountains of New Hampshire
http://www.qsl.net/kd1jv/
http://kd1jv.qrpradio.com