Glen,?
>>>did the test at -20dBm into the amp.
??? 470R?? -20 input gives -1.6dB out, 2nd harmonic is 49.6dB down
? ? 220R -20dBm in gives -1dBm out, 2nd harmonic is 41dB down.<<<<<<
What was the collector current of the 3904??? The peak gain is at 10ma.? It falls off sharply above that
and somewhat so below that.? That can introduce non-linearity.? ?So 220 is not best depending of the
applied voltage and bias.? Same for the emitter resistor on the output pair.
For best gain connect the bias resistor from the base of the first device to the emitter of the output.
The values may change but it provides DC feedback for operating point and puts the output pair in
the feedback loop.? IF the gain is set to reasonable (not more than 16db and lower is all that's needed)
then the distortion should be lower.
FYI allowing for the 45mhz filter (-4db) the total gain from the output of the 12mhz mixer to the output mixer?
should be around 11-13db as you get -20 up to -17db clean out of one and do not want more than maybe
-7db in to the other.? ?Overdrive is bad.
Allison
