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Revised version of the HF Antenna isolator


Chris Moulding
 

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:

http://www.crosscountrywireless.net/hf_antenna_isolator.htm

Regards,

Chris


david
 

Chris,

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: CrossCountryWireless@groups.io <CrossCountryWireless@groups.io> On Behalf Of Chris Moulding
Sent: 25 September 2020 19:57
To: CrossCountryWireless@groups.io
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:

http://www.crosscountrywireless.net/hf_antenna_isolator.htm

Regards,

Chris


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.

Regards,

Chris

On 28 Sep 2020, at 13:58, david via groups.io <zinc65=btinternet.com@groups.io> wrote:

Chris,

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




david
 

Hi Chris,

Thanks for the feedback. I managed to run the cores to ground on Arrow's
web-site, but they are listed as not available for order at present.
However, I have lots of ferrite left over from a noise-reduction campaign in
the shack and on the house's mains supply. If 4A11 is a suitable mix, I have
some equivalents. I might go for something a little 'stronger' to give me
better coverage of the lower bands. It _IS_ about experimentation, after
all.

Thanks for sharing your experiences.
Best Wishes
David, GM8XBZ

-----Original Message-----
From: CrossCountryWireless@groups.io <CrossCountryWireless@groups.io> On
Behalf Of Chris Moulding
Sent: 28 September 2020 15:02
To: CrossCountryWireless@groups.io
Subject: Re: [CrossCountryWireless] Revised version of the HF Antenna
isolator

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.

Regards,

Chris