On 4/19/16 7:27 AM, David Robbins wrote:
on the other hand... if doing this for SO2R operation only one of the
transmitters would be keyed at a time. You
would only have to worry about combined dissipation for multi-op stations or
expeditions sharing multi band
antennas.
Someone had a misconception on harmonics though a triplexer also. a radio/amp
say on 20m that generates
a 10m harmonic going into the 20m port of the triplexer would have that
harmonic filtered out by the 20m bandpass
filter on it's port so it would not get to the 10m port at any significant
level. What WOULD be a problem is if the
antenna or something near it was rectifying and creating a harmonic, that would
come back through the triplexer
to the 10m radio.
Depends on the rejection of the 20m bandpass filter. Let's take a
practical example: putting out 2kW on 20m, and the harmonic is 40 dB
down (virtually all amps do better than this when new and properly
adjusted, but...).
So we have +63dBm - 40 dBm = +23dBm at the second harmonic. Now, do you
want that harmonic "in the dynamic range" or "below the noise floor" in
your 10m receiver?
The noise floor in 3 kHz BW is going to be around -130 dBm. If you want
the harmonic below that, you're looking at a rejection of 150dB, which
is pretty impressive.
If you just want it within, say, 60 dB of the noise floor (knocked down
to -70dBm (roughly S9)), then you need only 90dB rejection. That's
still a lot, but probably practical with multiple stages.
In any case, you're going to be worrying about things like leakage
through the coax shield.
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