This was an interesting thread...but the problem has been
'solved', to the extent that it CAN be solved, by multi-multi
stations in competition.
I believe W2VJN, George, at INRAD, has assembled a book on the
topic. Think I saw it at Dayton. There's a picture of him at
W3BB's M/M station in Austin, on the cover. It's worth reading,
to avoid reinventing the wheel.
My experience has been that a combination of band-selective
filters and careful rig selection has resulted in workable
situations. Trying to run simultaneous CW & SSB on one band
will involve picking frequencies which don't have crud from
the other mode...and having low phase noise in both radios
is important.
Exactly the same problem exists in a M/M, where you have two
rigs on one mode. One is running, the other is tuning for
mults on the same band. Only one transmits at a time, but the
second rig has to be able to hear through the spurs and phase
noise from the run rig. This is hard to do, when the two rigs
are side by side.
On FD, my experience (since 1959) has been that you need to get
as much physical separation between in-band modes as you can.
It would be most helpful if none of the beams pointed directly
into any other of the beams. Picking up 10dB or more with antenna
location is a lot easier than trying to lose 10dB after the intermod
has begun.
For folks on the east or west coasts, the w1moo approach might work:
Use only monoband beams. Place towers on a N-S line such that when beams
are aimed west, only the ends of the antennas see one another. Use
RF chokes on all feedlines, at the beams, for common-mode decoupling.
I'd probably use the same approach in the midwest...but recognize that
you'll be turning the antennas, and won't get quite as good a result.
I would avoid trapped tribanders like the plague. Here's an example:
20m energy is picked up by the 10m tribander...it finds a partially
oxidized connection, and you have 10m harmonic content produced...and
delivered to the front end of your 10m station. Depending on the 20m
rig, it may be a discrete frequency, or may be broadband phase noise.
Similar scenarios can cause cross-band phase noise and intermod products.
Single banders are the way to go, even if you forfeit gain.
N2EA
jimjarvis@ieee.org
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