[Amps] measuring bandpass of a power amp with an NA

[Dan Sawyer]

I have a couple solid state RF power amps to test. One question is: What 
is their bandpass? I connected a network analyser drive to the output 
and then took the NA input of the collectors. Accounting for the 
impedance mismatch, this worked quite well, the amps showed good 
bandpass characteristics across the 2 to 30 MHz HF range.

I then connected the NA drive to the amps input and took the NA input at 
the transistor bases. This did not work at all, the NA showed close to a 
30 db loss across the range. What am I missing here? It would seem there 
should be at lease a discernible signal characteristic by this method.

Thanks - Dan