Fridge QRM

For discussion of ElectroMagnetic Compatibility and RF interference on 4 m

Fridge QRM

Postby G4MDC » Sun 29 Oct 2006, 22:52

I hope this might be of use to others.

I have had a well known make of fridge/freezer with CE mark and top ratings for low energy consumption etc - abt 3-4 yrs old I suppose. (Makers name begins with B)

For 4m it is a disgrace!! It radiates a sharply defined block of wideband noise from 69 to 73MHz and it is S9 at 10m away - enough to completely neuter 4m RX all around the house & the local area - I hear it as I approach home - the noise increases on my mobile rig.

At the far end of the garden (30m away = shack) it is still at least 10dB above background noise. I turn it off during contests - if I'm lucky I remember to turn it back on again otherwise I get in trouble for spoiling all the food!

I have looked inside - it's all buried in foam so I can't see the works or do anything about it without major surgery.

I think it should only be legal to operate it at least 100ft underground - imho. If it does pass the CE radiated requirements then the specs are not nearly good enough.

You do not want one like this if you like 4m operation!
Pity you even more if your neighbours have one...You can turn your own fridge off if required.

Fridge QRM

Postby G3TCT » Mon 30 Oct 2006, 18:16

Please don't be coy - I'm sure we'd all like to know the make and model number so we can avoid it like the plague!
Also you might like to write to the RSGB EMC people and see if they can take it up with the manufacturer.

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Postby G3PTU » Tue 31 Oct 2006, 00:32

If I think this is the make we have - 'German' all I can say ours does not make a noise.
We did have problems with the thermostat, which was simply a bi- metal on/off thing, - arcing.
I got a new one (very costly) and then arranged a Relay at the rear of the unit in a box to bring the comppresor on with the contacts on this relay not the thermostat direct.
These contacts have capacitors across them as does the therm contacts

We could tell it was the thermostat, as the arcing only took place if the Compresor was running and was brought on with the thermostat contacts. operating the "Quick freeze" switch (which usually simply shorts out the thermostat contacts) did not produce the arcing noise, which was both Rf based and audio band QRN

Touch wood - no further problems.

If I remember right the thing was perfectly straight forward wiring in a plastic box at the rear.
There is a power factor capacitor across the compresor motor.
Maybe yours has an "Electronic thermostat" or something?
Check the unit is earthed! Try Ferrite before going to all the problems I did above.
David Long
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Joined: Wed 25 Jan 2006, 17:55
Location and locator: IO93

Postby G4MDC » Thu 2 Nov 2006, 22:18

Sri. Big company lawyers earn lots more than big company EMC compliance engineers. What does that say?

There is no fancy stuff - an LED display (88 type) tells you the freezer temp and a bar graph the fridge temp. You can't program it beyond setting the desired temperature or turning it on/off.

I think it has some PIC or another inside. Some have said it's the LED drivers do this - same as modern traffic lights? Maybe...

Pity about the foam filling. I arranged a little outage for surgery but that stopped me dead in my tracks. I am not a miner.

The hash is not on the mains lead so little point in putting a ferrite on that. It radiates straight out of the plastic panel 1" high ~ 36" wide (lambda/4) at the top which has the display in it.

Pox on't (apologies Shakespeare)


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