BINGO!!! YOU GET THE PRIZE!!!
Common mode RF is a huge intra-station killer at a Multi-Multi field site.
Last year at W7PIG 6A WWA we used resonant antenna's fed with RG-213. We
used 2 tri-band yagi's that were 300 feet apart. Each yagi was fed with
a tri-plexer that had a ground rod to it. On 80 & 75 meters we used
inverted vees. On 40M we used a 2 element driven delta loop arrays. The
loops were optimized delta loops from the ON4UN Low Band DX'ing book.
They werevertically polarized and identical in resonance. The loops were
fed 90 degrees out of phase. The apexes were 45 ft high and the
performance was outstanding.
With everything being 50 ohms the performance of the bandpass filters
and coaxial stub filters were flawless.
We had CW & SSB run stations on 15, 20, & 40 meters. We had little or no
intra-band/station interference using a mix of older rigs.
I believe a pair of OCF Dipoles would be OK in a multi-two deployment. I
have my doubts that two stations could operate at the same band at the
same time. The antenna's would have to have adequate separation, the
ladder line would have to come straight down to a remotely located
antenna tuner, I would not try this without a decent ground at the tuner
to terminate to common mode RF prior to bringing a coaxial feed line
back to a common operating location.
Just my $.02.
Don KO7i
On 4/14/2015 1:30 PM, Jim Brown wrote:
On Tue,4/14/2015 12:36 PM, John Bescher via TenTec wrote:
And for your comment on the OCFD,
Off-center fed antennas put lots of common mode RF on the feedline,
which is bad news for interaction between stations.
Yes, stubs and bandpass filters can help reduce interference between
stations. So can a better rig -- cleaner TX and more bulletproof RX.
That's why K3s are the current weapon of choice, with rigs like the
KX3 and TS590 a decent second place.
Don't even think about bringing an el-cheapo do-everything wonder like
an IC706, FT100D, or newer equivalent Yaesus to FD -- you'll be
spewing trash into all the other stations!
73, Jim K9YC
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