Batboard

Hi There,

We have a
2002 GMC YUKON and a
2004 GMC YUKON

Both have UHF and Low Band CDM1250's. We get a terrible whine in these radios. We have tried numerous filters to get rid of the problem. Has anyone found the fix for this yet??

Thanks!

I have the same problem...It sucks...

Just a question, are the CDM'S remote mounted. We have a alternator whine problem on the remote mounts but never hear anything on the 1 piece units.

It's not so bad that we ever looked for the cause but it would be good to know why.

You do not tell us that when you get this noise. Is this noise during times when you have strobe lights running? Does the noise get higher in freq. when the motor revs?

The more information you can give would help.

Yes the radios are remote mounted.

The noise happens when all the lights, strobes and siren are off.

I will have to do tests for the rest of the answers to your questions. I will get back to you..

Thinking about it the trucks with the longest remote cables have the loudest alternator whine. The cables I shortened to about 4 feet have almost none, the units that are not remoted have none.

When I get time I am going to go to the loudest truck and put a head on it with a 1 foot cable and see if the whine goes away.

I will post the results after I do it but the more I think about it it's got to be the long remote cables

Is the cable from the control head to the radio flat, if so maybe try twisted pair wire (cat 5) instead, I just installed a FIRECOM 2 radio intercom system, and it came with flat wire, and now get some whine, I am in the process of replacing the wire with twisted pair to see if it cures the problem.

Yes it is flat 10 conductor with modular connectors, had a hell of a time finding the connectors and crimper. If I pin the noise down to the cable my next step would be to try twisted pairs at least for the mike audio. Cat.5 would not be a direct replacment as it only has 4 pairs, do not know how solid conductors would stand up to vehicle vibration.

Noise goes up with rpm's of the motor. Shut the motor off and noise goes away. Radio man ran all wires to same ground per Motorola instructions. Have installed a Kenwood filter right at the remote mount radio and a Newmar 150 amp filter right at the alternator. Also ran hot wires directly to the positive post of the battery with no luck. The alternators are 130 amp. We installed a new alternator on one of the vehicles and it made no difference.

We are considering dynamite, but we are told that gets messy.

Put a braided shield over the existing cable, grounded on only one end. Also insulate the outside of the shield. I know, a job and a half, but it may work and the flat shield braid is available.

Seems all the fire radios on the Verdugo system whine (Los Angeles/Glendale).

alternator whine is also known as FUEL PUMP whine. try installing a cap across the the fuel pump power leads to reduce the noise. just because it's RPM dependant doesn't mean it comes from the engine, that fuel pump cranks too...

Did some testing today.

The vehicle tested has a Motorola Remote Mount kit with a 7meter remote cable installed, control head has an RLN4756A Handset. There are no other mikes on the truck, nothing connected to the 16 (20) pin connector on the rear.

With the above setup at 1000 RPM there is a loud alternator whine that varies with engine speed and load. No it's not a bad alternator as I have 25 more trucks with CDM Remote Kits and they all do it. The only ones that do not whine are the rescues without remote mount kits.

I made up a 2 foot remote cable and found that the Alternator whine was almost gone, you realy had to listen for it and it could barely be heard.

Switched back to the cable installed in the truck and the whine returned.

The trucks are from 4 diffrent manfacturers, alternators from 3 diffrent manfacturers so there is no common thread there.

Cat.5 cable was sugested (need 10 conductors) Shielding existing cable also (a lot of work)

It's not that the transmissions cannot be heard, it's just anoying, got $25,000 quantars repeating the alternator whine

Anyone else solved this problem

I just thought of something, I should have tested with a 7meter cable that was not installed in the truck. At least that would have told me if the cable in the truck was picking up noise from outside or if the noise was cross talk between long cable pairs.

I am betting on crosstalk as even with the 2 foot cable there was a slight whine and the units that have not been remoted have none.

Will have to try again next week

Hey all, the plot thickens. The shop just replaced an alternator with the new improved "BINFORD BIGGER IS BETTER" alternator, wow can this thing charge.

But guess what, the low alternator whine that the truck had has now become so loud that it hurts to listen to it. This is a noise on Transmit only the thing receives fine.

To prove the noise is from the power supply I ran the radio from a 12 volt battery sitting in the cab of the truck with no whine at all. Put it back on the truck harness and the noise returned.

I keyed the radio with no mike connected using a breakout box on the mike connector, no noise. Connected the mike (actualy a handset) and the noise returns. Tryed the older GM-300 type handset and found that while it had some noise it was much less than the CDM type handset.

Compairing the 2 handsets it sounded like the CDM type was overdriving the audio input as compaired to the GM-300 handset. They could both do 2.0khz dev on a loud hard 5 (12.5 khz channel), just the CDM handset sounded overdriven.

Got to thinking about Mike Gain setings and looked at the default seting of 28.5, lowered it to 20 and found the noise greatly reduced and I still had no problem driving the radio into the deviation limit.

Droped the mike gain to 15 and the noise was again reduced without any real loss in transmit deviation, tryed 10 but then the deviation started do drop off so I set it back to 15 and left it there.

The reduction in gain does not seem to change the mike sensitivity at all it just reduced the whine.

The whine is still there in the siren but at least we can use the radio.

Anyone have any sugestions as to how to filter the DC supply that is used to power the Mike, I am assuming that is where the noise is geting into the mike. It would not be a big deal if I had to do a mod to every radio we own as long as it made them as quiet as the Mitrek's they replaced!!

I like the fuel pump idea. Not that you want to key right up on power up, but try transmitting when putting the truck in the "on" (don't start it!) position. Most vehicles (and Chev/GMC) will run the fuel pump for a couple of seconds. See if you hear the whine within those seconds.

Also, consider contacting some of the emergency vehicle manufacutres who do large scale installs such as Odyessy, and see what they have to say (if they say anything at all). Seeing that they do many of these a year, I am sure they have ran into something.

have you tried moving the ground? maybe even putting a choke coil on the ground wire? just a thought. if it was me, i'd also try a 1/2 farad cap on the power lead just for kicks. since there is no noise when you powered the radio from a battery sitting on the floor, the noise is DEFINATELY coming in through the wires, of which there are only two (three if you count the power sense wire). just 'cap' and 'choke' the crap outta those wires one at a time to see which one(s) cause the problem. that's my nickels worth.

Pj, it is a proven alternator noise, truck runs with alternator disabled and there is no noise. Have spoken to a few people about this and no one has completly solved it yet.

Eboe, Radio Grounds are clean and to heavy frame members of the cab, the cab has a heavy (1/0) jumper to the chassis. All grounds have been removed-cleaned and reinstalled with no change. I have tryed a Noise Filter that is a cap and choke in 1 package and it helped a little but not a cure. I realy do not want filters and caps hanging all over the place. A filter on each radio (3) and the siren could get ugly fast.

This is not just 1 truck, it's the entire fleet. Some worse than others but this one is the worst since they changed to a new larger alternator.

It's funny how the CDM handset makes it worse than a GM-300 handset, add a long control cable to the mix and it sounds real bad. Turning the Mike Gain down has helped big time on this truck, am going to try it next week on a few others but I would realy like to fix it at the source.

These same vehicles had Mitrek's in them with no problems at all, the only time you heard a whine from a mitrek was if the alternator had a bad diode. There is just something missing in the filtering in the CDM that the Mitrek had.

I'm glad this radio is not the Medical Telemetry radio, I can only guess what the whine would do to the ECG as the truck goes up thru the gears and the whine crosses the ECG modulator frequency

I would like to find a radio fix for this rather than attempt to cure each truck. I'm thinking a choke in the Mike power supply line from the radio, remember these mikes have amplifiers in them that are powered by a bias voltage on Mike High. If thats how the noise is geting in lets get rid of it at the source.

Wish I could reproduce it on the bench but I cannot figure out how to impose 500mv of AC ripple at varing frequencys on my bench supply.

At this point, I would:

A-Contact the vehicle manufacture

B-Dump the radios or see if there is a SRN on them about this problem with the band.

C-Dump the trucks

D-Find a CDM that is the same split as yours from another agency. Chances are all your CDM's are similar serial numbers and there could be a defect from the factory on that run.

yeah, you got a problem there. maybe it's choice "D" from pj's list. we have about 50 cdm's in the UHF band and never had any problems with ignition/alternator noise. we got em in chevys, dodges, fords, jeeps, you name it. we usually connect main power directly to battery, but i've hooked it up off the fuse panel a few times and still never had trouble. they never seemed that fussy about a power source or ground to me. i dunno, sorry.

We have serial numbers spread out over about 2 years in both low band and UHF so I do not think it is a production problem,

It's only when you add a remote mount kit (motorola) and a Handset. Take the same radio and put the head back on it or use an older GM-300 handset and the noise goes away.

Vehicles are from various manfacturers as are the alternators. All alternators are over 200 amp, the new "Binford bigger is better" is 395 amp and it's the worst.

Most vehicles get thier power directly from the master switch but I have moved some directly to the battery with no improvement, in fact 1 got worse as the alternator + lead was also on the battery.

As I said before, I can key the radio without a mike connected and it is quiet. As soon as I connect the handset the noise returns.

Lowering the Mike gain in the CPS has made a big change, need to listen to the few I have changed over the weekend to see if it is accpetable (noise VS slightly reduced xmit deviation)

Please let us know how you make out!!! Thanks!

We have requested through our area salesmanthat Motorola look at this problem.

He reports that he talked to someone at Product Services, they then had a conversation with the shop who is going to try something and if it doesn't work, they will open up a case against the plant for support.

Update:

I got to hear the truck with the new loud alternator on a call today and could not hear any whine at all and the transmit audio sounded better than the other trucks on the call.

If you have been following the thread I found that reducing the Mike Gain in CPS from 28.8 to 15 reduced the whine to next to nothing with very little reduction in Transmit Deviation.

I know 28.8 down to 15 sounds like a lot but in the service monitor it hardley made a diffrence. It does sound better, less distorted than before. I do not think I lost anything in fact may have gained deviation now that it is all voice not 3/4 voice 1/4 whine.

I guess that when you install a CDM type handset you need to adjust the mike gain. Anyone else care to try it and report back ?

I am going to do the rest of the fleet on monday and will report back.

As I previously reported I was going to adjust the Mike Gain down to 18 from 28.5 on all units.

Did this yesterday and after hearing the trucks on a few calls today I can say it is a great improvment. You can only hear the Alternator Whine if you are listening for it, it's almost gone.

Only strange thing was the units that are not remote mounted lost some transmit audio level where the remote mounts did not. I had to set the front mounts to 21 to make them equal to the remotes. Does not make any sense why there is a diferance but there is. But it did not make sense that the remote mounts had more whine than the front mounts either.

Anyway, I'm happy with how it turned out so far, going to listen for a while longer before I call it a cure.

Anyone else try it yet, want to confirm my findings

Well I am scheduled to try this fix next week on our vehicles. Let me know if you find anymore useful info. Thanks for your help!!

Anyone else try the mike gain adjustment to get rid of the alternator whine, I'M happy with the results of my adjustments.

Wound up reducing the gain from 28 to 18 and can hardly hear any whine at all. May bump it to 20 to get a little more gain for the soft spoken but it realy sounds good as is.

Note: This only applys to Remote Mounted CDM's with Handsets, Never had a problem with the front mounts or with regular mikes.

I'd contact Motorola and find out if SRN is published in the works, or you could be the start of one. This is obviously a radio accessory issue and should be dealt with as such.

I have the same vintage model year truck a 2003 suburban. I have several remote mount radios from Motorola and MACOM and I've never heard a peep of alternator whine on TX or RX.

I don't know what option package you have but my truck came with the heavy duty alternator and enough body grounding straps to strangle someone.

Then again I grounded my mounting try with heavy gauge ground to frame and use fully shielded NMO mounts.

The truck is whisper quiet on all bands.

FWIW I've had about 6 (small quantity, I know) different CDM1550 UHF mobiles moved around to different vehicles (trucks) within the past three years and never had a whine problem. Some have been wired straight to battery and chassis ground and some not. I would have your techs check all grounding points at the engine. Also, was any wiring changed before the CDM mobiles were installed? You could have a serious wiring problem.

Lord Windeshmere


As I posted previously, it is only on units with remote head kits that have handsets. It does not happen with standard mikes. It is on 20 trucks from 3 diffrent manfactures.

I have proved the noise comes in through the power leads. I am told that it is impossiable to have a 300+ amp alternator that does not make some noise. The original Mitrek radios had no problem dealing with it but the CDM has a problem with it.

Anyway, the gain reduction has cured it and I am looking no further than that. Was just wondering if the person who started this thread had tryed it and if it worked for him.

Yes it definatley helped a little bit. The audio level obviously went down a little. We are still playing around and testing. Thanks for all the help!!!

Every one of my radios has the remote mount kit. Well, you answered your own problem. Anyway, glad the issue was resolved.

We have the same problem to in 2 suburbans a 1987 and a 1993 both have horrible whine on our private 1 freq.

Well the mike gain adjustment did seem to work for awhile. But I think what it really did was lower the audio out of everything. The whine was down, but the dispatchers started saying they could't hear ME . (The book is still out as to whether that's a good thing or not) In the meantime we put the mike gain back and in fact kicked it up a little. (Guess that defines my ego)

Motorola said they would not open a case on this problem until we installed a MOTOROLA filter on one of the units. Well we did that and no change............except about 300 dollars out of our pocket.

So now Motorola has opened some type of case on this problem. Speaking as the guy who started this post, it is always nice to leave something to the next generation. I have a feeling those are the only ones that will receive benefit of any cures by the time Motorla solves the problem. Onward and upward as they say.....

Keep us informed as to what Motorola comes up with. We did loose a little audio with the Mic Gain fix but with few exceptions have had no problems with being understood.

Would be nice to be able to fix it the for good.

I have found that if you take mini 8 coax and use it as a DC feed line coming from the cigarette lighter it works well. Also coax coming from the Battery is better as it (the battery) is a big capacitor, the center conductor (+) is shielded by the outer shield (-)keeping down the noise

Is that going to handle the current of a high power radio?