On Saturday I helped commission what could be the first of several K2AV folded
counterpoise setups in WVDXA (West Virginia DX Association). The first
counterpoise was built by Tim, K8RRT wth assistance from W8TN. After it was
erected, I took the trusty bow and arrow and installed the inverted L radiator
in the trees. The radiator is about 55' vertical and the remainder
horizontal. The FCP is about 8' from the ground. The 1 to 1 transformer at
the feedpoint was built by Balun Designs.
Adjusting the radiator was uneventful, once I figured out the MFJ 259B was
receiving interference from a local AM station. Tim had one of those MFJ BCI
traps, so after reading the manual on this, we were able to tune the antenna.
We did have one self inflicted wound in this process. The wind kicked up a bit
and the temporary LMR 400 flex feedline was blown over close to the FCP while
we were in the shack testing with high power. Suddenly the SWR went haywire.
Oops. Inspection at the feedpoint revealed about 5 inches of the LMR outer
jacket was completely charred by an arc from the FCP to the coax shield.
Guess there are some pretty high RF voltages present on the FCP. Lesson
learned: keep other conductors, tree limbs, etc well away from the FCP. I am
anxious to see how it behaves the first time it gets wet.
Regarding the radiator adjustment, we started out with a length that, in my
experience of putting out more than a dozen of these 1/4 wave tree supported
L's, should have been long enough to allow trimming of the radiator. In fact,
the starting length was 5 or 6' longer than we usually go with. I still had to
add 9'. I suspect this is related to the wire length in the FCP. When I
build one for this QTH, I may increase the wire dimension slightly. Usually
the tree L's around here, with full foilage, will be lower in frequency than
they are after the foilage goes away, but this one was higher. It was not a
big deal, we were able to get good results.
Normally, I just cut the radiator (#12 or #14 THHN) to 130' and do the final
adjustments by trimming the elevated radials. Nomally, in my location and in
my trees, the elevated radials end up approximately 120' long. I might try to
adjust the FCP length on the next one just to see how it ends up.
K8RRT was using an inverted L, same location as this one, over a single
elevated radial about 5' or 6' over ground. Tim started on CW in 2008 and with
this simple antenna has confirmed 160M DXCC. His first DX QSO with the FCP was
CY9M, in just a few calls. Over the next few days, as Tim's work sked permits,
we will do some RBN testing to see what, if any, performance conclusions can be
drawn.
I have had really good performance with these tree supported Ls using two to
four elevated radials, and am anxious to try the FCP here.
Even if they are just equal to the elevated radials, the reduced footprint will
make room for more rx antennas.
Thanks to K2AV and W0UCE (who I met in Dayton this year) for the work on this.
73 Charlie N8RR
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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