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Extreme RF Gremlins - Can anyone assist?

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Trevelayan

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Hi all - I recently installed a new CB noticed I have a lot of noise on both my CB (and AM radio) that is coming from the engine area. Both the CB and Radio work fine when the truck is off, but when running, both have static and pops that match the RPM movement of the engine. My CB is now next to useless because of the sheer volume of noise, I have to squelch all but the loudest receptions out otherwise I just hear the buzzing. What could be causing this? It also happens (but not nearly as bad) when I turn the key but don't start the engine. Does this sound like a bad ground, battery, alternator, or something else I'm not thinking of?

I did a walk around with a handheld AM radio and the differences are clear:

Here's my setup:
  1. UNIDEN PRO 520 XL w/Standard mic
  2. TRAM 3500 Mag-mount 5'
  3. Center Cab mount, total height to end of antenna is 11.5' from ground, truck is 6.5'
  4. SWR is 1.3 across the band
ANL ON

The noise goes away completely when I unplug my antenna. When I max out the RF Gain with the engine running, I get a constant 2-3 bars of receive, I know there are transmissions I'm missing because I can hear them when I turn off the truck but leave the radio on. People are having conversations all around me but I can't hear them because of the stupid RF noise.

So far I have:

1. Moved the antenna location from top mid cab to everywhere else on the truck it will reach. I did notice, however, that the second I lifted the antenna from the truck, I had nearly zero static and could hear people talking. This was repeatable and didn't matter where I was at in relation to the truck.

2. Made an RF Choke with mix 31 ferrite on the antenna cable.

3. Grounded the power feed in 3 locations, first to the battery, second to the body itself, third to the seat base bolt

None of this worked.

My unit is also very sensitive to local RF interference from power lines etc. Here's a video, not sure if this is normal or not:

What are my options here? Is my truck just cursed?

Thanks!
 

prcguy

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Does it have the factory AM radio? A stock AM radio should have no interference with the engine running, they have figured things out at the factory for clear reception. More than likely the truck has had spark plugs or wires replaced with non resistor type and that is a common reason for ignition noise. Sometimes old broken down spark plug wires can also contribute to ignition noise.

The best recommendation is to use stock OEM spark plugs and wires which are are known to run quiet. There are aftermarket resistor plugs and wires but you never know if they are noisy until they are installed.
 

Trevelayan

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Does it have the factory AM radio? A stock AM radio should have no interference with the engine running, they have figured things out at the factory for clear reception. More than likely the truck has had spark plugs or wires replaced with non resistor type and that is a common reason for ignition noise. Sometimes old broken down spark plug wires can also contribute to ignition noise.

The best recommendation is to use stock OEM spark plugs and wires which are are known to run quiet. There are aftermarket resistor plugs and wires but you never know if they are noisy until they are installed.


The truck has had 2 owners and as far as I know neither of us has modified anything. The radio and spark plug wires should be completely stock.
 

tvengr

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A magnetic mount antenna does not give you a ground to the truck body. I would permanently mount the antenna in the center of the roof with a through the roof mount that gives you a good electrical ground to the coax shield. You will need a new antenna to do that. Also, make sure you have a good connection to the truck body with the negative lead of the radio power cable. The fact that the noise disappears when you unplug the antenna indicates the noise is being picked up by the antenna. Try to route your antenna cable to keep it as far away from the computer and computer cables as possible.
 

wowologist

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well one way you can check is to (obv. while the vehicle is parked) place the largest cookie sheet you can find under the antenna. If that lowers but doesn't cancel what your hearing, next with alligator clips and wire place one side on the cookie sheet and run the wire to the negative pole on your battery, if the sound stops completely you just have a ground problem. If it doesn't its more possible you have very low quality coax which is basically becoming an antenna.
 

prcguy

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The fact that the in dash stock AM radio is getting ignition noise means there is no CB antenna type or placement that will work, the noise must be snuffed out at the source, which is the spark plugs and its radiated by the spark plug and distributor wiring. Grounding the mag mount will have little or no effect because something is radiating the noise and the antenna is within the field of that radiation.

The truck looks like it has a few miles on it so I would carefully check the spark plug wiring for overall wear and also look at the make and part # of the wires and plugs. If its not OEM stock then you know what you must do.

A magnetic mount antenna does not give you a ground to the truck body. I would permanently mount the antenna in the center of the roof with a through the roof mount that gives you a good electrical ground to the coax shield. You will need a new antenna to do that. Also, make sure you have a good connection to the truck body with the negative lead of the radio power cable. The fact that the noise disappears when you unplug the antenna indicates the noise is being picked up by the antenna. Try to route your antenna cable to keep it as far away from the computer and computer cables as possible.
 

Trevelayan

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A magnetic mount antenna does not give you a ground to the truck body. I would permanently mount the antenna in the center of the roof with a through the roof mount that gives you a good electrical ground to the coax shield. You will need a new antenna to do that. Also, make sure you have a good connection to the truck body with the negative lead of the radio power cable. The fact that the noise disappears when you unplug the antenna indicates the noise is being picked up by the antenna. Try to route your antenna cable to keep it as far away from the computer and computer cables as possible.

I forgot to mention that I have tried re routing the coax, it didn't help either
 

kd1sq

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Another thing to check (after you fix the radiated RFI problem) is that the 12v from the battery isn't also dirty. Alternator whine and other noises are very annoying. Take a look on eBay or Amazon for an inline 12v car power filter.
 

jim202

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If your getting noise with just the key turned on and the engine is not running, the noise is probably coming from the fuel pump. You may need a filter to reduce the noise from it.

Jim
 

wowologist

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and it never hurts to go back to the start. Remove (disconnect the wiring of) the CB/scanner and anything additional you've added. Start it and check for the noise. If none re-add each component until you get the noise. Atleast then you'll have a reference point. And recording a say 30 sec audio file on your phone of it and posting it, may lead to more correct suggestions. Believe it or not "noise" is relative and generally the source has been found before.
 

Trevelayan

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and it never hurts to go back to the start. Remove (disconnect the wiring of) the CB/scanner and anything additional you've added. Start it and check for the noise. If none re-add each component until you get the noise. Atleast then you'll have a reference point. And recording a say 30 sec audio file on your phone of it and posting it, may lead to more correct suggestions. Believe it or not "noise" is relative and generally the source has been found before.

I would think given that the noise disappears when I unplug the antenna either the coax or the antenna itself is the issue, but everything so far points to stray RF being the culprit. I'll see if in can get a video of the noise itself.
 

wowologist

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Could you take a simple still of how you have the battery connection> it was a little jittery and most of it was blocked by the radio you were using. From the looks of it, you have a way to small + wire and it looks like you have a ground wire added? You should use the star topology for the ground, bring all your grounds from the items you've added to one point that was already a ground point for the built in radio system.
 

Trevelayan

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Could you take a simple still of how you have the battery connection> it was a little jittery and most of it was blocked by the radio you were using. From the looks of it, you have a way to small + wire and it looks like you have a ground wire added? You should use the star topology for the ground, bring all your grounds from the items you've added to one point that was already a ground point for the built in radio system.

I've had it set up 3 ways, all using the wires that came with the radio. The best way has been red to pos and black to the negative or grounded on the frame.
 

prcguy

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The problem is impulse noise radiated into the air, no grounding of the radio will have any affect. The problem must be dealt with at the source of the noise.


Could you take a simple still of how you have the battery connection> it was a little jittery and most of it was blocked by the radio you were using. From the looks of it, you have a way to small + wire and it looks like you have a ground wire added? You should use the star topology for the ground, bring all your grounds from the items you've added to one point that was already a ground point for the built in radio system.
 

wowologist

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This is what I'm saying. He has too many grounds. The "noise" was always there(unless a part is/has failed(ing), what he has done is inadvertently created an "antenna" for it (a ground loop). Remove the ground on your CB, if it powers on its already using a ground, same goes for any additional devices added in.
 

prcguy

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One last time, the problem is impulse noise radiated into the air and is being picked up by the antenna, just like any other signal from another CB and no grounding of the radio will have any affect. The noise problem must be dealt with at the source of the noise.

Either the old stock ignition components are worn out and causing the noise or someone has replaced the plugs and wiring with non resistor type.

This is what I'm saying. He has too many grounds. The "noise" was always there(unless a part is/has failed(ing), what he has done is inadvertently created an "antenna" for it (a ground loop). Remove the ground on your CB, if it powers on its already using a ground, same goes for any additional devices added in.
 

KevinC

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I suspect you have a Hemi, that is a very common issue with that engine. I'd do a Google search to see if others have been able to rectify it.

The Charger had VHF interference that was resolved, but I'm not sure if it would be from the same source as the truck.
 

Trevelayan

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I suspect you have a Hemi, that is a very common issue with that engine. I'd do a Google search to see if others have been able to rectify it.

The Charger had VHF interference that was resolved, but I'm not sure if it would be from the same source as the truck.


It's not a hemi, just a regular 5.9. It sounds like the only fix here is for an auto shop to isolate the source of the RF and fix whatever is causing it. I think my radio setup itself is solid.
 

prcguy

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I mentioned before to remove a spark plug and compare the part # to the factory or recommended resistor type plug and also do the same for the spark plug wires. If the part #s come back as different from factory and non resistor type you have the answer. If the plugs and wiring are stock factory type, then you might have some work ahead of you.


It's not a hemi, just a regular 5.9. It sounds like the only fix here is for an auto shop to isolate the source of the RF and fix whatever is causing it. I think my radio setup itself is solid.
 
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