Hi Dan,
Odd harmonics are caused by pretty much the same things as even
harmonics, namely distortion. In a push-pull arrangement, which it
sounds like your amplifier is (probably most transistor PAs using even
numbers of final transistors are push-pull) , the even order harmonics
are greatly reduced, so you would expect to see more of the odd order
harmonics than even order.
You are probably on the right track, looking at the bias. (If it is a
class B module, why doesn't it already have proper class B bias? Why do
you need to "add" it?) My first guesses are that one or both of the
transistors is incorrectly biased, or not functioning properly for some
other reason. How have you determined that the odd order harmonics are
out of spec? Maybe the transistors and their biasing is fine, and your
output filter is just not doing it's job. dB means nothing unless you
specify the reference. Do you mean -10dBc, where the reference is the
desired carrier on the fundamental frequency?
DE N6KB
>
> I am trying to add bias to a commercial class B NPN RF module. The input
> and outputs are 4:1 and 1:4 'binocular' transformers, feedback is a
> simple CR network. The output has a significant 3rd harmonic, about -10db.
>
> I have done research on the source of odd harmonics, however I can't
> find specific references. What is the root cause of odd harmonics, what
> would affect the level of harmonic?
>
>
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