Re: Revised version of the HF Antenna isolator



I have been following the discussions on the Antenna Isolator, following on from your article in RadCom on Loop Counterpoises, with extreme interest.
I am concerned at your (strong) recommendation of a Ferroxcube core with a 4A11 mix for the transformer. The part is identified in both the text and in the schematic, so I am sure it isn't a mis-print.
It is hard to source in the UK, anyway, but it seems to have a very low u' for LF work. Ferroxcube's data sheet suggests it has a u' of only 850. They rate the material for transformers from 10 - 1000MHz. For LF bands, I was expecting something around 3000 for u'. Can you put me right, here?

Best Wishes
David, GM8XBZ

-----Original Message-----
From: <> On Behalf Of Chris Moulding
Sent: 25 September 2020 19:57
Subject: [CrossCountryWireless] Revised version of the HF Antenna isolator

Following the publication of my recent article on loop counterpoises for low noise vertical antennas in the RSGB RadCom magazine, I've had a lot of feedback from RSGB members trying the design.

One question that came up a few times was could it be used with the non-resonant HF verticals such as the popular 43 foot vertical?

To work with those antennas the HF Antenna Isolator would need a 200 ohm output so I've re-designed it to have both 50 and 200 ohm outputs along with the 1 M ohm resistor and 20 kA gas discharge tube to provide protection from static electricity on the antenna.

It's now available.

The web page is:



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