Re: Topband: Ground loop isolator that passes DC
On 12/3/2021 3:53 PM, Andrew Ikin wrote: I guess what Chuck means, is a Ground loop due to the antenna end of the coax. screen being connected to Earth thus causing the feeder shield to become a loop antenna with the ground RF return path to Rx. Hence, resulting in excess noise pick-up. A serious common mode choke at the feedpoint is critical for this, effectively disconnecting the coax shield from the antenna for common mode current. But proper grounding and bonding in the shack and throughout the home are critical -- a primary cause of RF in the shack is failure to do that. There are differences with practice in the UK and EU with respect to connection of earth electrodes. This set of slides shows proper implementation in North America, which properly considers both power and antennas with respect to lightning safety. The laws of physics don't change at the water's edge. :) http://k9yc.com/GroundingAndAudio.pdf 73, Jim K9YC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground loop isolator that passes DC
Are you thinking of a Bias-T? MFJ sells them with some of their tuners. -73- FrankKG9H kg9hfr...@gmail.com > On Dec 3, 2021, at 5:53 PM, Andrew Ikin wrote: > > Chuck Hutton, > > Wrote on Dec. 3. > > That is exactly what I need so that power can be sent over coax feeds to > preamp at the antenna. > I cant find anything on eBay that mentions passing DC in an isolator. None > of the isolators I have will pass DC. > Does anyone know an isolator that passes DC? I would like to avoid building > one.> > > I guess what Chuck means, is a Ground loop due to the antenna end of the > coax. screen being connected to Earth thus causing the feeder shield to > become a loop antenna with the ground RF return path to Rx. Hence, resulting > in excess noise pick-up. > Normally common mode choke will be of benefit. But I would guess that Chuck > has already tried this. > > One option could be fit a 1:1 isolation transformer at the Rx input or into > the Bias T. Then use a floating power supply to the drive antenna pre-amp.. A > bias T that already has a common mode choke on the DC input would help too. > The Antenna Interfaces manufactures by Wellbrook have this choke feature. > > 73 > > Andrew Ikin G8LUG > > _ > Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground loop isolator that passes DC
Chuck Hutton, Wrote on Dec. 3. I guess what Chuck means, is a Ground loop due to the antenna end of the coax. screen being connected to Earth thus causing the feeder shield to become a loop antenna with the ground RF return path to Rx. Hence, resulting in excess noise pick-up. Normally common mode choke will be of benefit. But I would guess that Chuck has already tried this. One option could be fit a 1:1 isolation transformer at the Rx input or into the Bias T. Then use a floating power supply to the drive antenna pre-amp.. A bias T that already has a common mode choke on the DC input would help too. The Antenna Interfaces manufactures by Wellbrook have this choke feature. 73 Andrew Ikin G8LUG _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground loop isolator that passes DC
On 12/3/2021 1:34 PM, Richard Thorne wrote: The problem with lightening protectors is the blocking of DC and you can't send voltage to the switch, pre-amp or what ever your trying to power over the coax. There are protectors that don't block DC. A study of mfr catalogs will find them. 73, Jim K9YC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground loop isolator that passes DC
I 'think' what Chuck is trying to do is install a lightening protector at his coax entrance panel. The problem with lightening protectors is the blocking of DC and you can't send voltage to the switch, pre-amp or what ever your trying to power over the coax. My solution, good or bad, was to install a box outside my shack that includes a 12v power supply and the bias T. I inserted the bias-t on the antenna side of my lightening protectors. Inside the box I have an aluminum plate which is grounded to my system ground. If I can I'll post a picture as it shows how items are attached to the aluminum plate. Rich - N5ZC On 12/3/2021 2:32 PM, Chuck Hutton wrote: Hi - Many years ago I saw some ground loop isolators that pass DC. That is exactly what I need so that power can be sent over coax feeds to preamp at the antenna. I cant find anything on eBay that mentions passing DC in an isolator. None of the isolators I have will pass DC. Does anyone know an isolator that passes DC? I would like to avoid building one. Chuck _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground loop isolator that passes DC
Hi Chuck, Based on the application you mentioned, I suspect you’re looking for commercially available bias tees. MFJ sells Bias Tees. Don (wd8dsb) On Fri, Dec 3, 2021 at 3:33 PM Chuck Hutton wrote: > Hi - > > Many years ago I saw some ground loop isolators that pass DC. > > That is exactly what I need so that power can be sent over coax feeds to > preamp at the antenna. > > I cant find anything on eBay that mentions passing DC in an isolator. > None of the isolators I have will pass DC. > > Does anyone know an isolator that passes DC? I would like to avoid > building one. > > > Chuck > > > _ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Ground loop isolator that passes DC
On 12/3/2021 12:32 PM, Chuck Hutton wrote: Many years ago I saw some ground loop isolators that pass DC. There ain't no such thing as a "ground loop." It's a faulty concept, and using it to solve a problem are a bad idea. Most problems blamed on "ground loops" are the result of a failure to follow proper grounding and bonding practices. What problem are you trying to solve? 73, Jim K9YC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
