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

[CUTTER DAVID]

I've seen Cat 5 and 6 cable used up to 20MHz on one pair, power on another and data on a third, perhaps switching on a fourth pair. I know this works for distances of at least 20 metres and I wonder if it would be good at LF for 10 times that distance.  It's also very tough and modestly priced cable.  Can it be seen as a good use for this sort of application?

David G3UNA/G6CP

 
> On 05 October 2020 at 16:04 Grant Saviers <grants2 at pacbell.net> wrote:
> 
> 
> 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 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
> >>
> >>
> >>
> > 
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