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  #11  
Old 10-31-2012, 09:17 PM
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That would probably work too.

What brand fridge? My Engel definitely does not cause any issues. Both my fridge and HAM are wired to the same fuse block (under passenger seat) then direct from there to the battery.
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  #12  
Old 11-01-2012, 06:25 AM
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Yeah, what brand? Engel provides a chassis ground screw just for this reason. At a high level Engel's swing motor works on AC and there's a DC-fed inverter that drives it. There are then two supplies that provide DC to this motor driver, one a fairly simple AC/DC supply when on shore power and another DC/DC supply for 12V. They do this because the motor runs at 27V IIRC, so they have to boost the 12V.

It might seem odd, but they are usually quite a bit more noisy when used on battery than on the mains. So Engel built the case so the inverter and supplies live inside a shielded enclosure. If the fridge case itself is left floating or has a poor ground connection, the thing will be a huge RFI source. It's pretty important to do this if you run HF, there are three switching supplies in your fridge that will swamp your RX.

If you don't have an Engel it might not be exactly the same situation, but for Engel and ARB fridges a good test is to run the fridge on AC and see if the noise abates or changes, then you know it's just a matter of grounding the case. If this does not help, then you have to get more aggressive with chokes and bypassing. The majority of the noise should be fixed just grounding the case, though.
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  #13  
Old 11-01-2012, 07:12 AM
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Quote:
Originally Posted by DaveInDenver View Post
Yeah, what brand? Engel provides a chassis ground screw just for this reason. At a high level Engel's swing motor works on AC and there's a DC-fed inverter that drives it. There are then two supplies that provide DC to this motor driver, one a fairly simple AC/DC supply when on shore power and another DC/DC supply for 12V. They do this because the motor runs at 27V IIRC, so they have to boost the 12V.

It might seem odd, but they are usually quite a bit more noisy when used on battery than on the mains. So Engel built the case so the inverter and supplies live inside a shielded enclosure. If the fridge case itself is left floating or has a poor ground connection, the thing will be a huge RFI source. It's pretty important to do this if you run HF, there are three switching supplies in your fridge that will swamp your RX.

If you don't have an Engel it might not be exactly the same situation, but for Engel and ARB fridges a good test is to run the fridge on AC and see if the noise abates or changes, then you know it's just a matter of grounding the case. If this does not help, then you have to get more aggressive with chokes and bypassing. The majority of the noise should be fixed just grounding the case, though.
what a great response. thanks. With that description, it's sounding like a grounding issue more and more. It's definitely a "Huge RFI source".. I'll be messing with it this weekend and will report back. It's an ARB 47l model (50qt).

another question...any ill-effects for my radio by getting swamped with RF? I usually squelch it out.

Last edited by CardinalFJ60; 11-01-2012 at 07:25 AM. Reason: added fridge brand
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  #14  
Old 11-01-2012, 07:28 AM
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Attached photo of the connections on an Engel MT45, the chassis ground is in the lower right. I suspect most fridges will have this. If not, screwing a ground strap to the case, maybe under a bolt or something, would achieve the same thing. Although it's not necessarily going to be the case that all manufacturers take the time to design their cases for RFI. I wouldn't be surprised to hear Engel actually tests their fridges for EMI/EMC.

The noise is unlikely to be strong enough to cause any damage unless /maybe/ you touched the antenna to the noise source. It just takes inches in air to attenuate the noise from damaging to irritating. Or at least the signal strength goes down enough that your radio AGC can deal with it to protect itself. I should clarify, this is the case with noise generated from a fridge or computer or whatever, which is relatively low power. You would not want to hold your HT inches from a 50W mobile antenna while it's transmitting, that would likely ruin your HT.

The problem really with RFI like this is that a strong local noise source will desensitize your radio's RX. When you squelch out the noise or gain is reduced it will take a very strong signal from other radio operators before you hear anything. So a fridge 10 feet away might generate the same local signal strength as a regular station 25 miles away, for example.
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