> Using a filter after the transceiver is a good idea along
> with the one behind the amp.
In the 50's and 60's or earlier that might have been good
advice. Not any longer though.
Anyone who has ever looked at a modern Ham radio (i.e. a
real amateur transceiver like a Y K I) on a spectrum
analyzer is already aware they are typically down well over
50dB on harmonics, so any post transceiver filter is a waste
of parts. TVI worries from exciters went away along with
vacuum tubes. Exciter harmonic problems are now almost
non-existent
IF ingress into TV sets is now a non-issue, rendering the
old thought of IF frequency notching at the transmitter
useless.
As a matter of fact in most situations amps that meet FCC TA
requirements will even find a post amplifier lowpass
useless. Virtually all TVI is now fundamental overload, at
least with amateur amps that pass TA. Cases that still exist
center around direct off-air fringe reception, and the low
pass requirements are much different than they were 20 or 30
years ago.
It's a different world. The output filter has now largely
been relegated to the uses most people here talk about,
preventing radio-to-radio interference in multiple radio
environments like contests. In the rare cases where one is
needed, a stop frequency of 54 MHz and modest attenuation of
20-50dB is enough.
73 Tom
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