CB radio problems with 2005 Interstate

[herrgirdner]

This is a very nice rig; advertised and true fuel economy is 22 mpg. One problem I have noticed is that something in the engine produces powerful CB radio interference. When the engine isn't running, the CB works fine, but when the "ignition" switch is turned to the "on" position, some form of electrical noise blanks out the CB reception.
Any one have a clue as to what to do to fix this?
Oh, and I have tried three different CB radios. All have similar problems.

[jcanavera]

Wow, days of old. I remember that same problem with my old CB many years back. I think we used to use resistor spark plugs that were recommended as a way to cut down on the electrical noise. I've been gone from CB for so long that I would have guessed that newer radios and ignition systems would be much better.

Jack

[herrgirdner]

I could understand ignition noise if the power plant was not a Mercedes-Benz 5-cylinder diesel. I think it might be the high pressure pump, but don't know where it is. Any ideas out there?

[Jim & Susan]

High pressure fuel pump? In the fuel tank? I don't know much about diesels. Maybe diesels don't do it that way. My impression is that most electronic noise in an automobile is generated by electical devices associated with moving devices (alternators, generators, whatever type of "coil" you have). Mercedes makes a great product. You've talked to the dealer, right?

If the CB can't recieve at all with the engine running (as opposed to clicking or poping sounds), it is possible that a digital device of some kind is interfering. CB is in the 27 MHZ range. Are you running any type of computer near the CB, computer monitor, on board computer like one of those "mapping" devices? Have you tried moving the radio (CB) to another place inside or outside the van? Tried a different power source? ANd Antenna? Try each of these one at a time and see if you can isolate a specific area around the van, than look for electronic devices nearby.

Good Luck, Jim

[Tom Nugler]

Have to agree that the noise is likely caused by a digital device close to the radio or antenna.
The diagnostic scan tools we use in the shop to check the vehicles computers will blank out the normal radio signals in most cars. Newer radios and antenna systems are designed to help mitigate RFI, but I doubt CB technology has advanced much since the "80s.
Try moving the antenna to another location if possible. I assume the radio is near the dash and all the "Telemetrics". To check if the interference is coming from that area, try moving it away (out the door for example) to see if the noise changes. If not it's being picked up by the antenna. If it is, it's picking it up from near the area where it's mounted.
Hope this helps, but I haven't had to troubleshoot this type of problem in years.
Good luck, Tom.

[Skater]

Originally Posted by herrgirdner

This is a very nice rig; advertised and true fuel economy is 22 mpg. One problem I have noticed is that something in the engine produces powerful CB radio interference. When the engine isn't running, the CB works fine, but when the "ignition" switch is turned to the "on" position, some form of electrical noise blanks out the CB reception.
Any one have a clue as to what to do to fix this?
Oh, and I have tried three different CB radios. All have similar problems.

Is it a whining noise that changes with the speed of the engine?

How are you wiring the CB? Cigarette lighter, hard wire into a circuit, etc?

There are electrical noise isolators available at places like Radio Shack (stock number 270-051 - I happen to have one sitting here). It sounds like you may need one.

[Tin Hut]

I remember when installing my CB the manual said to reduce noise, connect the CB power directly to the battery rather than through a panel or fuse box. I don't have any noise on mine so far other than some of the crap you hear when driving through metro areas.

[Janets Husband]

Originally Posted by herrgirdner

This is a very nice rig; advertised and true fuel economy is 22 mpg. One problem I have noticed is that something in the engine produces powerful CB radio interference. When the engine isn't running, the CB works fine, but when the "ignition" switch is turned to the "on" position, some form of electrical noise blanks out the CB reception.
Any one have a clue as to what to do to fix this?
Oh, and I have tried three different CB radios. All have similar problems.

In many years of troubleshooting radio problems I have found out a few things about radio installation.
The first thing you must find where the noise is coming from; radio case, the antenna or the power input.
First thing to try is pull the antenna lead and then see what the noise is like. If it is gone or reduced then you are getting hit from the antenna or the antenna cable. Try to borrow a magnetic mount antenna and try different positions on the vehicle. Make sure your cable and connectors are in good shape and made up correctly.
Second thing to check is; get a second power source, be it a battery or external power supply and power the radio from that. If the noise goes away or is reduced, then it is coming from your vehicle power supply and you will need to put in some type of filtering available at your local CB shop.
Thirdly; if one and two did not do the trick and you have tried other radios then the noise is coming from some electronic device in the vehicle. Make sure your radio chassis is grounded use a 10awg wire to attach it to a good ground, shortest wire possible. If the noise was reduced by the ground then your on the right track. Try moving the radio to a different position in the vehicle and listen to how that works.
You may have to use one or more of these methods to clear up your problem. Yes, I have seen it where you can't get rid of the noise and you will have to live with it. I have also seen where the radio caused problems with the vehicle electronics and had to be removed, in one instance the radio being keyed caused the anti-lock brakes to stop working. Not good.
Good Luck

[herrgirdner]

I looked at the DC power distribution block off the positive terminal of the battery with an oscilloscope and saw 50 millivolts of what looked like commutator noise (square wave with overshoots) when the key is on and when the engine runs.
I couldn't draw that down, even with two 51000 mfd capacitors in parallel to ground.
Using a magnetic mount antenna on the roof of the airstream proved to reduce it so that a nearby CB could be heard. This showed me that the noise came into the set by the antenna.
But, the final solution proved to be grounding the shield of the coax near the antenna mount to the body of the auto with a short # 6 ground wire. It looks like a kludge, but it works!
Many thanks for your help.

[aa9zz]

What frequencies are used now on CB for travelers?

[Nuvite-F]

Originally Posted by aa9zz

What frequencies are used now on CB for travelers?

WBCCI uses CB channel 14 for communications between units on caravans and at the larger rallies. If you see another Airstreamer on the road you might try 14.

I have often found RVs traveling together using channel 15.

And of course for road information--often very colorfully described--the truckers communicate on channel 19.
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