I am currently experimenting with a full size (70 foot long)
40 meter dipole pair at 106 feet high for both 80 and 160 meter
receiving. I previously successfully operated the dipoles
as a "driven" array and tested the system using test source
consisting of a low 80 meter dipole about 1000 feet away.
It worked exactly as expected with deep nulls off the ends
and a high front to back ratio. I have recently been doing
some testing on 160 meters using just one of the dipoles
and I have not been able to see any improvement vs the
transmit vertical on over the air signals. The concept was
that the dipole, merely because it is horizontally polarized,
would best the vertical. I have seen this happen in the past
with low dipoles. The jury is still out on whether I can null noise off
the ends (in case noise is mainly from one direction). Previous
experiments with full size 160 meter dipoles at 30 and 60 feet indicated
that both received equally well and seemed to be omnidirectional. For
receiving with a dipole, it is important to decouple feedline noise. It
is unlikely that a transmit type choke balun will work for this. I use
flux coupled transformers for my receive dipoles. A nearby ham has a
DB-42 with the 80 meter dipole
option and he was recently complaining to me that he isn't
hearing as well as other stations a few hundred miles south.
So it certainly isn't a panacea. OTOH, he is listening through
the transmit matching network and balun that comes with the DB-42.
73
Rick N6RK
On 1/17/2017 9:32 AM, Jim Thomson wrote:
Has anybody tried using a 80m rotary dipole as a 160M RX ant ? Im thinking
it may well be quieter
than any dedicated RX ant I could come up with....on a city lot. There is no
way I can get adequate
separation between any 160m TX ant, like a .25 wave sloper, shunt fed
tower,etc, and a 160M RX array.
This assumes plenty of Z and esp RS on the 80m 1:1 choke balun... when used
for 160M RX. I dont use
QSK, just vox. So I would have to incorporate some high speed vac relay setup
to swap ants when on 160M RX.
It would be interesting to know if the RX concept even works. 80m rotary
dipole planned to go up this spring, on the
crankup..at 100 ft.
Jim VE7RF
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