On Fri,7/3/2015 7:03 AM, Greg Troxel wrote:
So, I wonder:
When you used the 250 ft spacing (and in the nulls), what kind of
measured coupling did you see?
We never measured anything. Rather, we followed "good engineering
practice," worked to find locations on our site where the antennas could
be colinear and in each others nulls, and as widely separated as
practical. We used resonant dipoles for 80 and 40, tribanders for
20-10. All had serious ferrite chokes at their feedpoint, all were fed
with big coax (RG213, RG11), all Amphenol connectors, carefully
tightened. Rigs were K3s with KPA500 amps. We also use bandpass filters
on each rig, which helps with harmonics. The result was that we could
have both CW and SSB on the same band.
What would people expect for power loss between the G5RV and the beam?
Based on other comments, distance, and the beam heading the wrong way,
I'd guess about 50 dB.
First, dump the G5RV and use resonant dipoles with serious ferrite
chokes. The chokes are probably good for 3-6 dB additional isolation,
maybe more. Without them, common mode radiation from the feedline fills
in the nulls of the pattern. Second, pay careful attention to all the
little stuff, like the quality of the coax and the connectors, any
switches that are in the way. When you're trying to get 50 dB down, that
little stuff can make or break you.
Note that our high power operation was for the California QSO Party. I
don't consider FD a high power contest -- I've never run more than 100W,
and for the last five years I've been doing it QRP.
73, Jim K9YC
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