Hi Dan, the binocular transformer causes the two transistors in the
amplifier to operate in a push-pull fashion. A characteristic of push-pull
design
is that the fundamental and all odd harmonics combine in phase while even
harmonics cancel.
The true source of the harmonics is within the transistors and they
produce both even and odd harmonics; the combining method reduces the
amplitude
of the even numbered ones through phase cancellation.
Good design would call for filters after the amplifier to reduce harmonics
to an acceptable level. The filter can be a simple tuned circuit as used in
tube type amplifiers to match the high plate load impedance to the lower
load impedance or a low pass filter with a cutoff appropriate for the
frequency of operation. Multi-band operation will require multiple filters.
I hope your answer is somewhere in the above.
73,
Gerald K5GW
In a message dated 11/18/2010 11:32:07 P.M. Central Standard Time,
dansawyer@earthlink.net writes:
All,
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?
Thanks for your help,
Dan
kb0qil
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