[CQ-Contest] Which Coax Jumpers Reduce SO2R Interference

[RCARIELLO]

Ken,
My gut feeling is the N to PL259 adapters. Any type of connector has some
leakage. With the adapters you have basically doubled the amount of leakage
points.
I am also trying to setup a SO2R station. My goal is to not hear the
transmitting station on the receiving station.
To find the stray RF around my equipment I used an open ended coax line
connected to a receiver as a wand. I was shocked as to how much stray RF was
present. A successful SO2R operation seems to be more difficult to achieve
then a Multi-Multi operation. This due to the many common RF tie points to
the antennas, Amps and even station operating positions. My two FT-1000mp's
hear each other sitting side by side while both receiving. I have not found
what level of leakage to expect from SO-239/PL-259 or N/N connector
combinations.

Posting some questions onto the RFI reflector I received these helpful
comments from Dale WA9ENA (former RF shielding engineer).

Isolation of typical braided shield coax (in the HF range):  70 to 90 dB
(varies with construction and type of braid)

Isolation of hard line:  100 to 120+ dB (except for leakage at connectors)

Isolation of commercial shielding "boxes" or enclosures:  100+ dB, except
for any penetrations

Frankly, the military - both on aircraft and on aircraft carriers - has
about
the same problem:  a lot of high power transmitters and antennas in close
proximity to each other and the need to be able to receive fairly weak
signals among all that racket.

The methods used to achieve that include very well-shielded bandpass
filters, hard line coax (for maximum shielding of each line), and as
reasonable orientation of antennas as possible.  The one thing you have in
common with Uncle Sam is that your antennas are about as packed together as
a lot of his are.

1.  Separate high-Q bandpass filters for each receiver, one filter per
band/part of band.

2.  All interconnects BETWEEN the filters and receivers done using hard
line and nothing but Type-N connectors.  (Use regular coax between the
relays and the filters, and between the relays and the antennas.  Again,
the antenna isolation is the lowest denominator, so put the bucks where
they are needed.)

3.  All switching done with relays having >50 dB isolation at 30 MHz.
(This is solely to make certain that less than 1 watt of RF from the amps
is coupled into any receiver bandpass filter or receiver front end.  One
watt or less is usually a safe value.)

I would be interested in hearing about your progress.
Please keep in touch.
Best of luck.
Rich AA2MF


----- Original Message -----
From: "Ken Widelitz" <widelitz at gte.net>
To: "Cq-Contest Reflector" <cq-contest at contesting.com>
Sent: Tuesday, February 01, 2005 2:43 AM
Subject: [CQ-Contest] Which Coax Jumpers Reduce SO2R Interference


> Although both my radios have stubs (double stubs on 40 meters) and
bandpass
> filters, I still suffer from more interstation interference than I would
> like when operating SO2R from my city lot. Thinking some of the problem
> might stem from my coax jumpers, I first went to all RG-214 jumpers from
> RG-213. I didn't notice much difference. I then went to Andrews F4 (1/2")
> hardline jumpers. It seemed to get worse. I just finished exhaustive
testing
> of the RG-214 vs. the hardline jumpers, and the numbers show, with one
band
> combination exception, the RG-214 is better. The only place the hardline
> came out better was transmitting on 80m and receiving on 40m. All other
> combinations favored the RG-214.
>
> I would have thought the better shielding of the hardline would have made
it
> better. The only factor that might have affected the hardline's results is
> that all the hardline came with N connectors, so I used adapters to
PL-259s
> on each end. These were new and the best quality I could buy.
>
> Any thoughts on why this is?
>
> 73, Ken, K6LA / VY2TT
>
>
>
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