Hi friends
I am trying to refurbish an CB amp. I am converting from class C to class AB
(adding Vbe polarisation) and intend to change the output trafo to avoid
saturation. But I have noticed a bad bhaviour at lower frequencies (below
14MHz). I have alreday added an network to lower gain (lower input signal)
at loer frequencies to compensate the gain-frequency behaviour of the MRF455
transistors (as stated in the MOT application notes). I have also lowered
the input (driving power) to avoid saturation. But I still find a high SWR
at the rig (input impedance change at the amp?) which lowers even more the
rig's output power.
So,
why does the signal distort that much (parasitic oscillations?)? and
when lowering input power and polarising properly the transistors, the gain
should be maintained, or no?
saturation to means, increase of current consumption and reduction of
impedance of the trafo (drastical reduction of Lmag); is this what is
happening? Where, at the input trafo? or the output trafo?, if I lower input
power I should be prevent saturation to some extend, but I see the same
behaviour.
I would like some comments. In the menatime I will continuo to play around
with the amp (change trafos) to see if soemthing becomes better.
Waveformas are at http://www.uv.es/~esanchis/radio/
Thanks for your help.
Stefan
EA5FY
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