I was going to reply to this earlier but, I tried to do it from
another email location which the AM Mailman did not know of so the
message was held up do to a technicality, HIHI
Any way it seems that Don, K4KYV has already replied but I will
just repost my message anyway.
The following is the message that I didn't send properly the first time.
Welcome Kim:
A slight drop in final plate current with modulation is not
uncommon. It generally is indicative of a slight drop in high voltage
especially when the modulator and the final use the same high voltage
power supply. It does not necessarily mean that the modulation envelope
is not expanding as it should if viewed on a scope. In other words if
the high voltage is dropping by 5% then the plate current would be
expected to drop by 5%. If it's more than 5%, I would look in to
regulating the HV supply a little better or repairing what is wrong with
it.
This phenomenon, of plate current change, (up or down), can also
occur due to RF feed back or poor neutralization and this would be a
problem to correct. A class C final that is not properly neutralized
will have phasing products during modulation that will cause excessive
band width and if a synchronous detector is used at the receiver it will
detect the products and add them to the standard AM products thereby
generating distortion.
GL, 73, John, WA5BXO
