Topics

Rf problem


David Dudley
 

Hi Chris I am having problems with rf on my radio New fridge freezer is the problem and I can't put aerial anywhere else as I only have a small garden and  my aerial is a Westbrook 1530 Antenna.please any help appreciated thank you


Chris Moulding
 

Hi David,

I had exactly the same problem you have.

We have a Samsung fridge freezer that radiated a lot of RF noise. The problem is that to increase energy efficiency it uses a switch mode inverter power supply to power the fridge and freezer refrigeration units and the internal fans. In our case the inverter is mounted in a metal box on the top of the fridge freezer so that the mains cable hangs down from it making a pretty good antenna for radiating RF noise.

In our case I fitted one of our Mains Filter units to the mains cable. This stopped the RF noise getting into the rest of the house wiring. I had to add an extra three clip-on ferrite cores to the mains cable directly where it runs into the box on the top of the fridge freezer to clear the rest of the noise radiating from the mains cable. Testing with the three ferrite cores on their own the RF noise levels were still too high and it needed the combination of Mains Filter and ferrite cores together to bring the noise down to a workable level.

The fridge freezer is situated about 3m from the end of my Terminated Inverter U antenna so it was a severe test for the Mains Filter and extra ferrite!

Regards,

Chris


Facility 406
 

"Hi Chris I am having problems with rf on my radio New fridge freezer is the problem and I can't put aerial anywhere else as I only have a small garden and my aerial is a Westbrook 1530 Antenna.please any help appreciated thank you"

Check with the RFI (radio frequency interference) group, this issue is discussed almost daily.

RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi

Kurt


David Dudley
 

Hi Chris can you send me one with modifications please I will pay with pay paypal


David Cutter
 

Hi Chris 

What type of core do you recommend?  How many turns?

David

G3UNA

On 01 May 2019 at 16:37 Chris Moulding <chrism@...> wrote:

Hi David,

I had exactly the same problem you have.

We have a Samsung fridge freezer that radiated a lot of RF noise. The problem is that to increase energy efficiency it uses a switch mode inverter power supply to power the fridge and freezer refrigeration units and the internal fans. In our case the inverter is mounted in a metal box on the top of the fridge freezer so that the mains cable hangs down from it making a pretty good antenna for radiating RF noise.

In our case I fitted one of our Mains Filter units to the mains cable. This stopped the RF noise getting into the rest of the house wiring. I had to add an extra three clip-on ferrite cores to the mains cable directly where it runs into the box on the top of the fridge freezer to clear the rest of the noise radiating from the mains cable. Testing with the three ferrite cores on their own the RF noise levels were still too high and it needed the combination of Mains Filter and ferrite cores together to bring the noise down to a workable level.

The fridge freezer is situated about 3m from the end of my Terminated Inverter U antenna so it was a severe test for the Mains Filter and extra ferrite!

Regards,

Chris


Chris Moulding
 

If possible don't use a clip-on ferrite. It's better to cut the cable and fit a new mains plug after the ferrites are slipped over the cable.

The ferrite I recommend for HF RF noise suppression is the Wurth 74277290.

https://katalog.we-online.de/pbs/datasheet/74277290.pdf

This was originally designed for suppression of medium wave noise affecting broadcast receivers from neon signs. It works down to 300 kHz and typically needs two or three turns through it to give a high level of suppression peaking at 2 MHz but still covering the full HF bands.

Radio amateurs rate the 31 material core for HF use but compared to a 74277290 it's like using a Polo mint!

Regards,

Chris


David Cutter
 

I've used #31 for LF coax choke following Jim Brown's recommendation which worked well but required 7 large diameter turns through 5 large cores to get the several thousand ohms suggested. Quite an expensive and bulky solution.  This was for common mode rejection in an antenna system.  To cover HF as well it required 2 chokes in series of different topology..

I'll give that a try for my next choke.  Thanks, Chris. 

David

G3UNA

On 02 May 2019 at 10:25 Chris Moulding <chrism@...> wrote:

If possible don't use a clip-on ferrite. It's better to cut the cable and fit a new mains plug after the ferrites are slipped over the cable.

The ferrite I recommend for HF RF noise suppression is the Wurth 74277290.

https://katalog.we-online.de/pbs/datasheet/74277290.pdf

This was originally designed for suppression of medium wave noise affecting broadcast receivers from neon signs. It works down to 300 kHz and typically needs two or three turns through it to give a high level of suppression peaking at 2 MHz but still covering the full HF bands.

Radio amateurs rate the 31 material core for HF use but compared to a 74277290 it's like using a Polo mint!

Regards,

Chris


David Dudley
 

How many do need Chris and where do I get them from thanks


Chris Moulding
 

It depends on the diameter of the mains cable that you are threading them on. The diameter of the inner hole in the ferrite core is 12.5 mm or 1/2".

If you can get two or three turns of cable through then you only need one, if you can only get one turn i.e. cable straight through the hole then you will need three of them.

One supplier in the UK is RS Components: https://uk.rs-online.com/web/p/ferrite-rings/1234234/

Regards,

Chris


David Cutter
 

If this is to be done inside an enclosure, eg a mains distribution panel or a switch box, etc, then the outer sheath of the cable can be removed and just thread the inner wires through the core.  That might help if you have a particularly fat cable.

David G3UNA

 

From: CrossCountryWireless@groups.io [mailto:CrossCountryWireless@groups.io] On Behalf Of Chris Moulding
Sent: 10 May 2019 18:01
To: CrossCountryWireless@groups.io
Subject: Re: [CrossCountryWireless] Rf problem

 

It depends on the diameter of the mains cable that you are threading them on. The diameter of the inner hole in the ferrite core is 12.5 mm or 1/2".

If you can get two or three turns of cable through then you only need one, if you can only get one turn i.e. cable straight through the hole then you will need three of them.

One supplier in the UK is RS Components: https://uk.rs-online.com/web/p/ferrite-rings/1234234/

Regards,

Chris


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