"CD" wrote
My concern with the harmonic frequencies is mainly
protecting the transmission system and also not interfere with other
sister stations. From what I've read so far, some harmonic frequencies
might couple to the transmitter input and that can affect the output.

The usual mechanism is when the 2nd harmonic of an active transmitter (F1)
mixes with the fundamental of a nearby station on F2 to produce an IM
product at 2*F1-F2. This can occur in a nonlinear output stage of F1, and
harmonic filters normally have no affect on the in-band IM product that is
generated.

The control is to filter the external fundamental signals from entering F1's
output stage via the antenna connection, so they are not present there to
generate spurs.

Hmm..also, wouldn't the harmonic filters normally be
part of an antenna tuning unit?

It is more closely connected with the harmonic "signature" of a given tx,
and so is usually supplied as part of the tx system. The tx OEM has to
certify that his tx meets specs for harmonics and spurs, and couldn't do
that unless the performance of the filtering network was under his control.

RF

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