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

[Grant Saviers <grants2@pacbell.net>]

My DX Eng 4 sq (12v over RG6 to preamps) has had infuriating random arc 
noise for years and the W3LPL explanation makes great sense to me as the 
reason.  I did silicone grease the F threads but followed the "CW 
advice" to not flood the connector so I have a project to do that.
Hi-Z had a separate 12v power lead on their whip preamps, but with DXE 
selling them that seems to have disappeared.  Now powered by a bias T 
over RG6.
Heading into the PNW monsoon season, so need to get it done.

Grant KZ1W
Redmond, WA

On 10/4/2020 18:33, K4SAV wrote:
> 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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