Hi Holger
We made extensive use of open wire feedlines at ZL6QH to connect antennas
scattered over a couple of hundred acres of farmland. We often used the same
poles to run up to 4 open wire feedlines to multiple antennas in a similar
area. The feedlines were constructed to be nominally 600 Ohm impedance and
were typically separated from each other by a metre or so on the same pole
and cross arms. Have a look at slides 18 and 19 in the pack at
http://www.zl6qh.com/cvradiofest.pdf for a close view of how these open wire
lines were configured.
The station was used regularly in multi-operator multi-band contests in
which up to 5 radios, antennas and bands were used simultaneously. There was
some residual cross talk between the feedlines on the same route and poles
but it was often difficult to distinguish this from cross talk between the
antennas. The cross talk was generally only noticeable when working weaker
signals and close to the harmonic signal from a transmitter on a lower band.
Operators were encouraged to choose frequencies that did not cause harmonics
to fall on the run frequencies of other stations on the higher bands. The
use of antenna tuners on the lower bands (configured in a low-pass mode)
also assisted to reduce the level of the harmonic QRM.
So, based on our ZL6QH experience, what you are proposing should be
feasible, assuming there is sufficient separation between the feed lines on
the same poles. However, before going to a lot of effort to build the new
lines I would recommend that you do an experiment to confirm the expected
level of cross talk by setting up a couple of temporary terminated 600 Ohm
lines in parallel (at the proposed physical spacing) and measuring the power
coupling between them.
73
Brian VK3MI ZL1AZE
_____
Message: 6
Date: Sat, 16 Mar 2019 15:08:29 +1300
From: "Holger Hannemann" < <mailto:holger@9h3m.com> holger@9h3m.com>
To: < <mailto:cq-contest@contesting.com> cq-contest@contesting.com>
Subject: [CQ-Contest] station re-building, distortion when multiple
600 Ohm lines in parallel?
Message-ID: < <mailto:000001d4db9d$28e3e780$7aabb680$@9h3m.com>
000001d4db9d$28e3e780$7aabb680$@9h3m.com>
Content-Type: text/plain; charset="us-ascii"
Hi all
Additionally to the interesting discussion around coax cables and double
shielding I have another question.
We have re-modelling / extension plans here at ZM4T. The new tower locations
will require to bridge distances of 150-500 m with feedline between shack
and antennas. Coax but especially hardline costs a multiple times here in
New Zealand what is does in NA or EU. Therefore we evaluate to run 600 Ohm
ladder lines for the long distances. For about 100 m we would have four of
those 600 Ohm installed in parallel utilising the same support poles. That
means they only have a small distance/separation between them.
When contesting, it is very likely that two or more of those ladder lines
would be used in parallel for transmission and receive at the same time.
Does anyone has experience with potential distortion when operating parallel
running open feeder lines?
Thanks in advance
Holger, ZL3IO
_______________________________________________
CQ-Contest mailing list
CQ-Contest@contesting.com
http://lists.contesting.com/mailman/listinfo/cq-contest
|