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
Re: Topband: RX Power over Coax
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
Re: Topband: RX Power over Coax
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 - Original Message - From: "Lee STRAHAN" To: "Dennis W0JX" , topband@contesting.com Sent: Tuesday, October 6, 2020 7:15:56 AM Subject: Topband: RX Power over Coax Hi Dennis and top band interested folks, The very first amps I made for myself were using an external power wire. Using external power required some pretty heavy choking on each end of that added wire. I started experimenting with power over the signal coax. I could not see or measure any difference in noise floors with usually new components including coax. After a number of years' experience I now believe that if there was a weakened connection that would allow micro arcing then that same weakening would cause a perturbation in the operation of the array also. This resultant lack of performance would signal the operator that something was wrong. All the elements in most of my designs are required to operate and feed signal continuously to the combiner regardless of the direction selected so all would be susceptible. It's my opinion as I have not witnessed any arc sounding interference or noise floor increase that I could not identify as external to the array. Keep in mind I have not done yearlong in depth projects to veri fy my observations or real levels of possible noise. I am sure a fully loaded environmental laboratory could do this but so far I cant. If one desired to power the amplifiers externally any noise current that would be developed on a single wire must then also flow into the power terminal where it would encounter a generally large filtering capacitor across the power rails of the amp and its ground side. The noise current would then flow right through to the amp ground terminal and be impressed upon the array ground rod. This also is not a desirable thing as the ground rods exhibit impedance and a noise voltage could then show up as added to the element signal. Series inductance in this line can help. So it appears the best answer to this is to use a second coaxial cable or 2 wires to supply the voltage and power ground to the amp. Now with both + power and ground wires feeding power to the amp one can use common mode filtering to remove the noise flowing to ground and an additional inductance to decrease any noise voltage on the center of the coax carrying the plus power voltage. Its true, I have built a couple versions of Hi-Z amps with RG-6 external power connections for Tim at K3LR. He has serious common mode filtering on these power lines as well as the signal lines and I suspect serious filtering on the supply voltage as well. There may in my mind be some advantage of external power in keeping multiple transmitter signals off the array power as well. Its also true that I have a small circuit board I can install on the back of a second coax connector on the New version SMD amps. The board offers 5000 ohms of common mode protection on 160M and a series inductance for the center wire providing 1 mHy inductance giving some isolation for power supply or induced center conductor noise. No need for expensive giant ferrite cores on the coax lines. Common mode protection is built in to both the coax power input and the coax signal output. So due to lack of interest I have not championed the idea of providing this external power capability. I think the reputation of success with Hi-Z and its power over coax stands for itself as to the existence of the problem at Hi-z or the public would be letting us all know something is wrong. Trust me on that. I cant speak for any other designs. In addition to this noise incursion possibility I have uncovered another possibility of micro arcing unrelated to the coax. As it stands most of these arrays are powered from an in shack power supply. With some of these arrays drawing 1/2 an amp or more if using a wireless remote relay setup. This causes a significant voltage drop on power wires leading to the array. With the power supply grounded at the shack and the Hi-Z amps grounded at the array elements there is often a voltage difference between shack ground and element ground caused by the power supply current flow. This voltage difference causes a current flow in the ground rod. In more than 18 years of operation I will soon have to replace my original Steel Tee post mounted elements as the ground end of the posts has been eaten away by what I assume to be electrolysis. My theory is that there could be noise developed on the ground rod at the element caused by this voltage dropped between the shack and the array causing the e lectrolysis. Noise on the ground rod shows directly up as received signal. My new version of SMD amps have been de
Topband: RX Power over Coax
l make an interesting experiment even if its inconclusive. I can modify the new amps for this external power on direct to me special request.. 73 Lee K7TJR Hi-Z Antennas Subject: Topband: RX Power over Coax 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
Topband: RX Power over Coax
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
