Topband: RX Power over Coax
I just wanted to agree that using coax feeders for power as well as rf can lead to noise. I have a lot of beverages and other receive antennas, some of which are thousands of feet from the shack, and I also use (probably unnecessarily complex) switch units. This has meant that I have had to use 48V to ensure reliable switching. I use CATV hardline for the 'main' lines and flooded RG6 for 'local' lines. I have never had problems on the hardline, but the RG6 has often been noisy. I am of the opinion that this happens at F connections even when the joint is very well prepared and sealed, but this is so far unproven... 73 Roger VE3ZI _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: RX Power over Coax
On 10/7/2020 7:45 AM, Grant Saviers wrote: Rick, Did you CM choke the power and signal leads? or the whole cable? Grant KZ1W I should clarify that the CAT-5 was only used to drive relay coils. It did not power up a preamp, because I did not need a preamp. In place of a CM choke on the RF coax, I used a flux coupled transformer, either a Mini-Circuits T9-1 or a homebrew one using a binocular core. (The transformers were used with Beverages). The substantial drop in signal level when the relay was de-energized indicating that the transformer was providing sufficient de-coupling. Using a separate DC feed allows the option of using a flux coupled transformer instead of a CM choke. There seems to be a knee jerk reaction in favor of using CM chokes vs flux coupled transformers. A small transformer has very little interwinding capacitance and could provide more isolation than a CM choke. And with Beverages, it is needed anyway. 73 Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: RX Power over Coax
Does anyone have an audio recording of what micro-arcing sounds like they could post somewhere? Sam(N3XZ) -Original Message- From: Topband [mailto:topband-bounces+samjos=epix@contesting.com] On Behalf Of GEORGE WALLNER Sent: Wednesday, October 07, 2020 10:05 AM To: Dennis W0JX; Dennis W0JX via Topband Subject: Re: Topband: RX Power over Coax I use a 600 foot long run of CATV coax to power a remote pre-amp at the DHDL-s, delivering +12V/100 mA via the central conductor (return via the shield). Prior to installing the F plugs I spray the cleaned and prepped ends of the coax with DeOxIt. I also spray the inside of the female F connectors. I add a small amount of SS-30 grease to the thread of the each F connector, tighten the connector using a small wrench (!) and tape the outside of each mated F connector. So far, no no noise, micro-arching or other. Further, I believe that the DC current keeps the contacts vetted, which makes them more reliable. 73, George, C6AGU/AA7JV On Tue, 6 Oct 2020 04:44:51 + (UTC) Dennis W0JX via Topband wrote: > Regarding the issue of voltage over coax to power the preamps used at the > base of short verticals, Lee, K7TJR, developed an alternative power feed > system for his new SMD preamps using a separate RG6 coax. Apparently, K3LR is > using such an approach to avoid sending voltage down the coax in his 8 > element HiZ array at his contest station. > DXE has begun selling the new version 2 preamps but the description in their > catalog does not mention this separate power feed system. The older HiZ > preamps, and the YCCC preamps, can probably be modified to the voltage with a > separate wire from the combiner box to each vertical antenna preamp. > One question I have with this approach is whether an external power wire > would also need a common mode choke on it. Perhaps Lee could offer some > opinions on this alternative power approach. > 73, Dennis W0JXMilan, OH > _ > 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
Re: Topband: RX Power over Coax
Rick, Did you CM choke the power and signal leads? or the whole cable? Grant KZ1W On 10/7/2020 07:22, Mark - N5OT wrote: In my head this is becoming "101 uses for old network cable" which is great because I've got a ton of it coiled up neatly and set aside but not thrown away :-) Thanks topbanders. Still working on this year's vertical. It will be ready for CQWW is the plan. 73 - Mark N5OT On 10/6/2020 6:20 PM, Richard (Rick) Karlquist wrote: Exactly right. I had trouble with "critters" chewing my coax. Nothing bad happened until it rained. Then the rain got into the coax and the water interacted with the DC voltage on the coax; terrible noise. With the DC off, there was no noise even when soaked. I converted the DC feed to CAT-5 cable and the problem disappeared. Another advantage of CAT-5 is that you get 8 conductors, all independent of the RF coax and the earth ground. Also, for whatever reason, critters don't like it :-) The RF coax was eventually stuffed thru 1,000 feet of cheap sprinkler pipe repurposed as "conduit". Good enough to keep the critters out and rain out. But I elected to keep the CAT-5 for DC. 73 Rick N6RK On 10/6/2020 3:09 PM, donov...@erols.com wrote: Hi Lee, Your testing will be inconclusive unless you inject water into your connectors, or you could just move to Maryland where we get at least 45 inches of annual rainfall and it gets into everything thats not well waterproofed 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
Re: Topband: RX Power over Coax
In my head this is becoming "101 uses for old network cable" which is great because I've got a ton of it coiled up neatly and set aside but not thrown away :-) Thanks topbanders. Still working on this year's vertical. It will be ready for CQWW is the plan. 73 - Mark N5OT On 10/6/2020 6:20 PM, Richard (Rick) Karlquist wrote: Exactly right. I had trouble with "critters" chewing my coax. Nothing bad happened until it rained. Then the rain got into the coax and the water interacted with the DC voltage on the coax; terrible noise. With the DC off, there was no noise even when soaked. I converted the DC feed to CAT-5 cable and the problem disappeared. Another advantage of CAT-5 is that you get 8 conductors, all independent of the RF coax and the earth ground. Also, for whatever reason, critters don't like it :-) The RF coax was eventually stuffed thru 1,000 feet of cheap sprinkler pipe repurposed as "conduit". Good enough to keep the critters out and rain out. But I elected to keep the CAT-5 for DC. 73 Rick N6RK On 10/6/2020 3:09 PM, donov...@erols.com wrote: Hi Lee, Your testing will be inconclusive unless you inject water into your connectors, or you could just move to Maryland where we get at least 45 inches of annual rainfall and it gets into everything thats not well waterproofed 73 Frank W3LPL _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: RX Power over Coax
I use a 600 foot long run of CATV coax to power a remote pre-amp at the DHDL-s, delivering +12V/100 mA via the central conductor (return via the shield). Prior to installing the F plugs I spray the cleaned and prepped ends of the coax with DeOxIt. I also spray the inside of the female F connectors. I add a small amount of SS-30 grease to the thread of the each F connector, tighten the connector using a small wrench (!) and tape the outside of each mated F connector. So far, no no noise, micro-arching or other. Further, I believe that the DC current keeps the contacts vetted, which makes them more reliable. 73, George, C6AGU/AA7JV On Tue, 6 Oct 2020 04:44:51 + (UTC) Dennis W0JX via Topband wrote: Regarding the issue of voltage over coax to power the preamps used at the base of short verticals, Lee, K7TJR, developed an alternative power feed system for his new SMD preamps using a separate RG6 coax. Apparently, K3LR is using such an approach to avoid sending voltage down the coax in his 8 element HiZ array at his contest station. DXE has begun selling the new version 2 preamps but the description in their catalog does not mention this separate power feed system. The older HiZ preamps, and the YCCC preamps, can probably be modified to the voltage with a separate wire from the combiner box to each vertical antenna preamp. One question I have with this approach is whether an external power wire would also need a common mode choke on it. Perhaps Lee could offer some opinions on this alternative power approach. 73, Dennis W0JXMilan, OH _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
