Ground loop, fridge and radio?

[fbksurferjoe]

Ok so this is an annoyance more than a major problem. I have a decent grasp of electronics so when I wired up my fridge I ran a dedicated power source and ground to my 2nd battery. I have a fuse block that also runs off my 2nd battery and this too has a dedicated power. However I did not run a dedicated ground to it. I grounded it to the frame and I also grounded the 2nd battery to the frame.

The fridge runs direct to the battery the fuse block is on the other side of the 4runner.
So I listen to am Radio, I'm old school I guess. When my fridge runs I can no longer hear that Station until it cycles off.
Is this a ground loop or is the am antenna picking up "noise" from the fridge?

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[paranoid56]

i had similar issues and similar issues with my LED lights. i used a few Ferrite Core Cord Noise Suppressor on my cords coming from the lights and to my fringe and it helped a tone.

 

[fbksurferjoe]

Sorry, yes static noise. Only on am, I have switched over to fm and there is no static. Thank you for the suggestions I will give them a shot and report back.

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[OuterLimits]

Sorry, yes static noise. Only on am, I have switched over to fm and there is no static. Thank you for the suggestions I will give them a shot and report back.

If the static is on AM and not on FM it is most likely RFI originating from the fridge and being received via the AM antenna. You need to stop the RFI at the source.
I would wind the power wiring to the fridge on a ferrite core (as close to the fridge as possible).

I would also try running a ground strap from the fridge chassis to the vehicle ground to see if that would help the fridge chassis shield the noise originating in the motor.

Is this a portable radio or vehicle radio? If it is a portable radio, you can often turn the radio to null out the interference. You can also get highly directional external loop antennas to null out interference.

If this is your car radio, you can use a portable AM radio with its directional AM antenna to pinpoint the source of the RFI. You can also unplug the antenna from the radio to determine if the static is entering the radio via the antenna or the 12v power.

If it is the antenna, there are inline filters available, but they are not always effective. If it is from the 12v wiring, wind the radio power line through a ferrite core, as close to the chassis as possible.

RFI can sometimes be a bear to deal with. Good luck

http://www.popularmechanics.com/cars/how-to/a84/1272491/

https://www.howacarworks.com/accessories/identifying-and-suppressing-radio-interference

https://www.crutchfield.com/S-D7t3p...car/noise_suppressors_installation_guide.html

https://www.amazon.com/Radio-Stereo-Inline-Antenna-Filter/dp/B00820Z7I0

 

[fbksurferjoe]

It's funny I have a radio at home that does the same thing.
I just bought a jumbo pack of ferrite chokes. My wife saw the amazon order and said what the heck are those. Thank you for the info, I'll get to the bottom of this noise.

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[fbksurferjoe]

Ok, so ferrite didn't solve the problem. I will attempt a ground from the motor to the vehicle chasis

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[DaveInDenver]

Ferrites would only prevent the RFI from being coupled on the cables, either through the power to the radio or them becoming antennas. If the motor is radiating as the source then they won't have solved it. You could try snapping the ferrite beads on the radio antenna feedline. Depending on the mix it may not have too much impedance in the AM band. Even if it does attenuate commercial AM, it would be a test anyway.

It also may not be a grounding issue, but improving it and removing loops isn't going to be a bad thing to do. Have you tried running the fridge stand alone not connected to the vehicle power at all with its own battery?

There are 4 tests we do on electronics for the military and aerospace defined by MIL-STD-461. Two are radiated and conducted susceptibility and two are radiated and conducted emissions. Point here is that EMI/EMC is half the time being a source (as the aggressor) of noise and the half being immune to it (as a victim). You can do everything you can think of to prevent one mode, coupling on cabling or ground loops, only to find that the motor itself is acting like a small radio station and creating a local EM field that is being received by your radio just any other broadcast.

Therefore you may have to shield the fridge (or radio antenna). Do you have one of those aluminum foil sun shades by chance? Or perhaps something else large like that made from aluminum foil or maybe some extra metal window screening? You'd make a Faraday cage that fits around the fridge. I don't get much interference from my Engel. It's not a motor per say but the Sawafuji swing compressor still does create a field. It's also wrapped with a transit bag which has a reflective fabric on the inside that might be helping, too.

BTW, I wasn't kidding about shielding the antenna, although wrapping it in a metal foil would be a big hammer approach that would render it useless as a radio. But if you can narrow the spectrum that the motor creates you could build a notch filter for that range of frequencies and fix it that way. Assuming it's actually coming in on the antenna, that is. These are essentially what fugitive linked to, usually called inline filters.

 

[fbksurferjoe]

Wow, so much info, I love it. Ok that makes sense. It does have a transit bag with the foil on it. I have not run it stand alone yet. I think I may pull off the 2nd battery ground that goes to the chasis and see if that does anything. That would effectively isolate the batteries from each other completely.
My other concern is I want to put in a mobile vhf radio in my rig and am afraid I will get interference like the am radio. However if I reach back to what I learned about radios when I was a boyscout I believe it falls more within the fm band? Which seems to be unaffected on my stereo.

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[DaveInDenver]

Since you need the batteries connected to each other with large cables there's not too many easy ways to isolate them that won't take large components to tolerate the current. So I think you're best off trying to keep the battery connections very low impedance and isolate the fridge and/or radios from each other on their feeds, if it's a power related issue. You really should trace back and try to eliminate problems at their source with interference like this anyway.

What you're doing by running the fridge on it's own power as a test is seeing if the noise is coupling on the power or not. Just narrows down the problem and helps figure out a path to solve it.

It's less likely you're going to interfere with a VHF FM radio, which is as you mention near (2m ham is 144 to 148 MHz) the commercial FM commercial band (88 to 108 MHz). If it's motor noise anyway. Depending on the fridge you have you may have an inverter (making AC from DC) or power supply (making 12V from 120V, which wouldn't apply here) inside, which may be the source of the noise and that could be fairly high frequency.

But if that was going to be a problem it would have shown up on FM radio. Also FM generally speaking is more tolerant of broadband noise like this. It's not impossible that you will find 2m radios will have noise, though. When you have interference issues you'll sometimes find your transmissions are noisy (alternator whine is a very common occurrence for example), so you need to ask other hams to give you signal reports. That's also true on CB, though.