Are you thinking of a Bias-T?
MFJ sells them with some of their tuners.
-73- Frank KG9H
kg9hfrank@gmail.com
> On Dec 3, 2021, at 5:53 PM, Andrew Ikin <andrew.ikin@btconnect.com> wrote:
>
> Chuck Hutton,
>
> Wrote on Dec. 3.
>
> <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.>
>
> 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
>
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