Hi Serge,
Have just joined this reflector. I have used a D3W for possibly 12 or more
years. It's stacked about one metre above the TH5 and about the same distance
below the Create 6ele 6M beam. Until about 5 years ago the D3W worked just
fine with very low SWR on 10 and 18 MHz but not so well on 24MHz. Then like
your D3W it started to display poor SWR's. I guessed the traps were zapped but
then in the summer the SWR was generally OK - a fair weather antenna! I had it
down and checked it over, replaced the coax but it was just the same. The poly
support stay that is fixed between the 24 and 18MHz traps to hold the antenna
in a horizontal position looked a bit dirty with moss, so I wondered if this,
when it got wet was detuning the 24MHz elements/traps and therefore upsetting
the whole antenna. I changed it for 180lb fishing line and everything was
again OK for a couple of years. A few weeks back, it was back to square one.
The fishing line looked clean. This time I have opene
d all the traps and can find no fault there. Cushcraft traps are easy to get
into. Just drill a 3mm hole where the punch marks are and slide the inner part
out. When reassembled put a few punch marks beside the holes you made and
cover the holes with self amalgamating tape. The antenna is on a 3 metre pole
while I work on it - no poly element support stay and the SWR is again
excellent on 10 and 18MHz. However 24MHz is about 1.3:1 and adjusting that
element will not improve it - 24MHz has a very broad bandwidth. I would like
to be able to measure the resonant frequency of the traps but cannot think how
that may be done. Ideally they should be just LF of the lower band edge but I
note that on the A3WS beam, exactly the same traps (type TB1) are used for all
three elements. I would have expected there to be a difference. Any advice on
how to measure the resonant frequency of the traps would be welcome. I have
GDO, frequency counters etc.
I have not offered you any solution to this problem but you have an account of
what I have done to try to overcome the problem that we both share. I do still
think that the support stay may be the culprit. When the temperature rises
above freezing I will pursue the matter further.
John
G3HTA
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