The one "multiband" antenna one can use in a multi-transmitter
configuration is the flat-top with open wire feeders and a
*Link coupled* tuner. The link coupled tuner is a bandpass filter
that significantly reduces harmonic/broadband noise just like the
"Q" of a single band antenna.
73,
... Joe, W4TV
On 2019-10-10 7:44 PM, Don Wilhelm wrote:
Bob,
Bandpass filters at each station will help a lot, but they do not have
infinite out of band rejection.
There is still a huge benefit with single band antennas. My club uses
both.
Last Field Day (3F operation) one station got on the air with a
multiband vertical, and all other operators jumped on that operator to
shut him down quickly! The multi-band antenna radiated harmonics of the
radio. Even though the transmitter met the -43 dB harmonic required by
the FCC, the proximity of the multiband antenna to other antennas caused
problems (that station was not using a bandpass filter).
So for Field Day multi-station operation, single band antennas, bandpass
filters and transmitters with low phase noise are important. We were
not able to orient the antennas end to end due to space considerations
at the EOC site, so we had to compromise on that, which makes the other
factors very important.
I need to point out that as an experiment, a 2nd station used an antenna
on 20 meters separated from the main 20 meters, and we were able to
operate one on CW (K3) at the same time as the other station (Icom) used
digital and SSB modes. We had some mutual interference, but it was
minimal. The K3 did not interfere much with the Icom due to the K3's
low phase noise, but the Icom did raise the background noise level on
the K3.
73,
Don W3FPR
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