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 <[email protected]> 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, [email protected] 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 > >> > >> > >> > > > > _________________ > > Searchable Archives: http://www.contesting.com/_topband - Topband Reflector > _________________ > Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
