Re: Revised version of the HF Antenna isolator

Chris Moulding

Hi David,

I've tested the 1:1 transformer on the 160m band (1.810 - 2000 kHz) with barely measureable loss.

I agree that the toroid will have too low a u for the 2200 and 430m bands.

The toroid is in stock at Arrow Electronics but from many emails I'm receiving quite a few people are having difficulty finding the toroid ontheir web site.

We do have a small stock here so if anyone is having difficulty sourcing one contact me by private email.



On 28 Sep 2020, at 13:58, david via <> wrote:


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

Join to automatically receive all group messages.