Hi, Charlie.
5-10 feet longer than quarter wave is starting to sound pretty normal. I
would be interested in comment on the idea of telling people right off to
start with 151 feet (46m) and prune back.
This beyond-quarter-wave length is useful, because it increases current
density (the integral of the current) in the vertical while raising the
feed R, which is an efficiency factor. I have been trying to get actual
wire up and wire out length measurements from people but especially in the
trees, getting the L's length has been very approximate after all the
pruning. A couple places I know of where getting the L in the trees where
they couldn't be seen in a HOA neighborhood, and pruned was hours of
struggle and THE accomplishment for the day. No way that's coming down to
measure it.
73, Guy.
On Mon, Jul 30, 2012 at 9:37 AM, Charlie Young <weeksmgr@hotmail.com> wrote:
>
> 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
>
>
>
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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