A while back I added a Tokyo Hy-Power HL-1.5KFX amp to the station out in my
shop. Prior to that I had mainly been using the station for listening to
code practice from W1AW on 40 although I did make a few contacts on 6-meters
a year or so back.
When installed the antenna was resonant in each band and with an SWR at
resonance of 1.1:1 in each band, although the antenna never seemed to do
well on 20 from day one.
It took me a few weeks to get the auto-band switching feature working as
there was no pin-out diagram for the Yaesu input, so during that time I was
just on 6-meters.
Once running I noticed that the minimum SWR on all bands had risen from
1.1:1 up to around 1.5:1 which by itself is not bad, but it gave me a
substantially narrower band width on each band.
On taking the antenna down I discovered the drain holes were too large in
the matching network at the base of the antenna and had provided a great
entrance to the new home the Paper Wasps built. However being that close to
nearly a KW on 50 MHz did prove hazardous to their health and opening up the
matching network I found it packed with nests and crispy Wasps. OTOH I had
to remove the innards of the matching network and give it a good scrubbing.
Even then their glue didn't all come out although what was left was only a
few marks on the toroid cores.
After cleaning the matching network, reassembling the whole works and
adjusting the resonant point of 40 from the bottom end of the band to mid
band I put the antenna on a 15' temporary mast with the aid of W8LSS and
WD8BPT for testing. I find every thing is pretty much back to the way it was
except for 15 meters. It is now resonant about one MHz below the bottom
band edge and the minimum SWR is around 1.7:1. The other bands are back to
the 1.1:1 at resonance. My guess it there is something inside the loading
coil for 15 meters as it and the top hat are the only things specific to
that band..."I think". "Up there" it would take very little added
capacitance to shift the frequency by quite a bit. OTOH the thing should
cover the whole 15 meter band with no adjustments.
Hy-Gain does have an 800 number as well as a "contact us" on their web site,
but it'll probably be mid next week before any one there would take a look
at an e-mail. I'd like to get this fixed and back on the tower this week end
IF possible <:-))
Any "socially acceptable suggestions" would be appreciated.
BTW:
The AV640 uses a combination of stubs, top hats, and loading coils near the
top hats. This allows each band to be independently tuned with no apparent
interaction between the tuning on different bands.
The antenna is designed to operate with out an elaborate set of radials and
is supposed to be mounted at least 8' off the ground and a minimum of 5'
above metal objects such as metal roofs and rain gutters. Of course, like
most antennas of this type (multiband and no radials) it is a compromise.
OTOH it does do fairly well after getting the original kinks out of it.
Still, it's not going to make anyone "king of the mountain", but it makes a
handy antenna for my shop and as a back-up.
TIA & 73
Roger (K8RI)
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