[Elecraft] K3 FD report in high RF (K3 vs Flex 6xxx)

[Jim Brown]

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