Topband: Common mode choking of beverages - which side of grounded shack entry panel?

[K4SAV]

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 at 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
>
>
>