W3LPL said "A peripherally related issue: Running DC power through the
same coax cable as low level RF signals is asking for trouble."
I agree completely. Here is my story of trying this. Maybe this will
help if anyone has the same problem. I did this with one low signal
level receiving antenna system. (I later abandoned that approach.) I
had cleaned some connectors with WD-40. The surface tension of that
stuff is so low that it runs everywhere and you can't wipe it all off.
It runs and carries very fine particles with it. I had bad noise
problems and it was difficult to find. An ohmmeter connected to the
disconnected RF cable showed a resistance more than my ohmmeter could
measure, but when applying a voltage to the cable I could see a small
amount of leakage current and it increased rapidly with applied
voltage. The current wasn't constant either and that was the problem.
A variable current through a high impedance creates noise. The leakage
impedance measured at the operating voltage was about 20K ohms.
Lessons learned:
1. Don't clean anything with WD-40 that has to be low leakage.
2. W3LPL said it already, you are asking for trouble when running DC
down a low signal level cable.
Jerry, K4SAV
On 10/4/2020 6:47 PM, donovanf@erols.com wrote:
Hi Mark,
It can be very challenging to reduce common mode adequately to preserve
the directivity of low signal level antennas such as the YCCC 9 circle.
My preferred approach is to bury all cables interconnecting the amplifiers
at the base of each vertical and the phasing combiner/controller, and the
cables running from the shack to the phasing combiner/controller
As a minimum you should use the nine common mode chokes strongly
recommended in the YCCC 9 circle array users manual.
YMMV if you're QTH or nearby locations produces high level RFI.
My preferred approach is to kill all RFI at its source.
A peripherally related issue: Running DC power through the same coax cable
as low level RF signals is asking for trouble. There's a high risk of RFI
generating micro-arcing if any trace of water or moisture enters the connectors.
If you must combine DC and RF into the same coax cable, you must
to stuff your connectors with silicone grease to eliminate all air gaps. Water
very easily migrates down the threads of CATV F-type connectors unless
the threads are also protected from water migration.
73
Frank
W3LPL
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