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Alternator Noise Through Antenna?

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jluisi86

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All of a sudden, I am not starting to hear alternator whine on my CMD1550LS+ UHF mobile. The antenna is mounted on the fender, where it’s been for a few months now. I started trying to figure out what was causing this issue and came down to this:

As long as the antenna is NOT attached to the body of the vehicle, I have no noise, once I install it back on the vehicle the noise comes back. Sometimes it’s worse; sometimes it’s barely noticeable which also is throwing me for a loop.

Is that still considered the standard alternator whine? I have the radio installed for about 1.5 years and never had an issue till yesterday. Anyone have any ideas on what I should do? Thanks
 

jackj

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Sounds like you have something called a 'ground-loop'. What happens is that you get current flowing between the two grounds connected to your radio, the antenna and the power ground. Check your radio's power ground, looking for a corroded connector or contact. You may have to bond the fender to the rest of the chassis or move the antenna to another location on the truck. If all else fails, try using a mag-mount to isolate the antenna's ground from the truck's body. Good luck, ground-loops can be a real ***** to find.
 

jluisi86

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I tested a mag mount antenna and no noise. I also disconnected the alternator once and tried it and no noise. The problem I now have is some times there is no noise and I didn't change anything. So some of my tests might not hold water. I will go over all the grounds I can find and check. The vehicle is a 2011 GMC Sierra so everything is pretty new still. Thank you for the direction!
 

K5MPH

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Ground

Check your ground to the radio make very sure you have a good ground,the reason the noise stop when you take the antenna off is because the noise is coming in on the ground side and not the rf side of the antenna.
 

jluisi86

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I disconnected the wires to the radio and ran a brand new wiring harness directly from the battery to the radio and the noise is still there... I need to still double check the truck battery grounds but Im running out of things to do. Anyone?
 

jluisi86

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I'm really at a loss now, I checked every ground and every looks like new and is tight. I don't understand why one day everything would be fine and the next have all this noise. I would rather not put a filter on it, I would like to fix the issue. Should I try to change the alternator out?
 

NCFire11

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I have roughly the same problem. The mobile radio is grounded to the chassis using the factory harness. The 1/4 antenna is mounted near the trunk using an L-bracket. Now, this is a good amount of spacing between both grounding points. Would running a wire from the ground for the radio to the actual L bracket for the antenna help this problem? Perhaps giving it a direct point to point ground?

Don't mean to hijack this thread, but our problems are very similiar.
 

mmckenna

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I'd suggest taking the antenna mounting apart and checking all that for corrosion. Pay special attention to underneath the mount. Looks for signs of water intrusion into the coaxial cable.

While electricity will take the path of least resistance, in this case the power wiring harness back to the ground, some of it can find a way back through the antenna ground. Corrosion under the mount or wet coax can cause these sorts of issues. One of the problems with the bracket mounts, the coaxial cable, where it has it's jacket stripped and conductors exposed, isn't always protected well enough from the weather.

I'd also suggest trying to move the ground point around for the power. I had a 2005 GMC Canyon that when I grounded the negative power feed directly at the battery post, I'd get alternator whine. When I grounded it on the sheet metal body, no alternator whine.
 

mmckenna

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On that note, it's usually a good idea to do some preventative maintenance checks on your gear from time to time. I try to check the following every few months:
Check antenna SWR.
Take antenna off mount and clean underneath.
Take whip out and clean where it connects to the antenna base.
On the Larsen NMO mounts, actually remove the whip from the cone and clean the end of the whip, the inside of the cone and the set screws, water can settle inside and cause corrosion.
Clean the NMO gasket and use some armor-all on it.
Check all the power connections.
Clean battery posts. Actually disconnect the battery completely and clean the posts off until they are clean and lightly shiny. Clean the inside of the battery cable connectors also.
 

jluisi86

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Everything is in brand new condition, it has only be installed for a few months with all new equipment. I had a spare antenna cable and tested that with the same noise coming through.

I really dont understand how this could all of a sudden pop out one day... I am going to do a few little things tomorrow and see if i have any change.
 

jim202

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Hey guys, before going off on some wild tangent, have you considered that it might just be the vehicle?

The first question I have to ask is how old is the vehicle? If more than 4 or 5 years, it might be wise to check the ground wire from the battery to the vehicle body. There should also be a ground wire from the engine to the body of the vehicle.

My next question is how old is the battery? Most batteries will loose their internal resistance and not have the capacity storage over time. The battery no longer acts like a big filter cap and keep noise down.

One of the first indications that your battery has reached end of life is that the car clock in the radio will loose it's time when you start the engine. If it gets cold, you might notice the engine turns over real slow. You might also notice that the headlights go dimmer when you pull up to a traffic light.

There are some other checks you can do, but we need to know some of the details before going any further. After making sure the vehicle is good, only then would I go after the radio, antenna, power feeds and the like.
 

jluisi86

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The vehicle is a 2011 GMC Sierra 1500, nothing has been change/replaced electric wise. Battery is OEM of course. I have never had an issue with the vehicle not starting. There are two ground wires attached to the battery terminal, one large 6-8 gauge running directly to the engine, the second is a 10 gauge running to the main fuse box. Both of those ground wires look great, but i cleaned them anyway with contact cleaner.

I have a power block mounted inside the cab with 6 gauge wire directly attached to the battery that runs everything i have installed. (Whelen LED Lightbar,siren, radio, scanner and some other small LED lights. This setup has been installed for over 1.5 years with no issues, everything that i wired up still looks like new.

The price of a new alternator is cheaper then a battery i would buy (Optima)...
 

12dbsinad

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I agree with the ground loop scenario. When the "whine" is present does it change pitch when you rev the motor or is it a consistant tone? A thing to try, take a piece of wire ( same gauge if you have it as the power cable) temporarely ground it to the antenna mount and then ground the other end to the exact spot where the negative for the radio is grounded (im assuming the battery) and test. If the noise is gone then its a ground loop issue and can be solved by permantly running that wire to the radio grounding point.

Also, im assuming the noise is during tx, or is it only rx? or both? If its only recieving issue it could be other issues like microphonics within the radio itself.
 
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jim202

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The whine follows the revs of the motor. The noise is RX and TX.

OK, next step is to see if the alternator is working correctly before pointing any fingers. This will require the use of a digital volt meter.

The first test would be to measure the battery at rest voltage first thing in the morning before even starting the vehicle. Write this voltage down. Should be about 12.5 volts or so.

Next, start the engine and measure the battery voltage again. You should see between 13.8 and 14.5 volts. A more normal reading is 13.6 to 14.0 volts. Write this value down.

Now lets start putting a load on the alternator. Turn on the headlights on low beam. Measure the voltage. Write it down.

Next, turn on the high beam headlights. Measure the battery voltage. Write it down.

Next, turn on the A/C or heater on high. Measure the battery voltage. Write it down.

Only a couple of other items left to add to the mix. Leave the high headlights on, leave the heater or A/C on high. Now turn on the windshield wipers. Again measure and write down the voltage.

Last item left is to turn on the direction indicators like your making a turn. Leave everything else turned on. Measure the battery voltage and write it down.

Now while you have a max load on the alternator, take your volt meter and put it on the AC scale and measure the battery voltage. What your looking for is how much ripple is in the output. This should be down in the 50 milivolt range or less. Anything higher will point to a bad diode in the alternator.

With all the voltages recorded, take a look and see just where the voltage starts to drop off. If the alternator can't hold the headlights and heater at full blast, then you could have a bad voltage regulator. As just about all the vehicles today have the voltage regulator built into the alternator, I would get some auto shop to verify you have a bad alternator.

Another test I always make is to turn on the headlights and make a voltage measurement from the battery post and then from the battery clamp where the wire is. Have found poor connections between the battery post and the wire connector many times was causing strange electrical problems.

Once your happy that the alternator is working the way it should, I would then start looking at the radio, it's ground connection and the antenna ground connection. Most of the mounts today rely on a good ground right at the antenna. If your mounting the antenna to a fender to the trunk, it might not have a good connection. You might have to add a ground strap between the body and the fender or the trunk lid itself.

Notice I used the term strap and not a wire. Your looking for a low impedance connection, not just a ground connection. The flat strap made from the braid of a piece of coax is much better than a number 14 piece of wire. Solder a lug on each end and put a screw into the metal to finish the connection. I use some anti oxidant compound on these connections to keep long term corrosion from doing in your work over time.

Have fun. Make the noise go away.
 

Tech792

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I once had a similar problem with a CDM1250 VHF. After installing in 2 separate lease vehicles I always had alternator whine. Mostly on transmit. Could never pinpoint the problem. Installed in a third lease vehicle and the whine was still there. So one day I decided to change out the radio to a different CDM programmed the same identical way and the whine was gone. Something in the radio I suppose not filtering? Try a different radio and see if that solves the problem.
 

CCHLLM

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I concur with Jim202. Sudden alternator whine is a sign of something changing in the alternator and connected wiring.

If the symptoms were not appearing intermittently before the continuous onset, and a check of the physical wiring doesn't reveal a problem, the most likely candidates are the alternator diode array or the regulator, or both.

If the whine is a single varying whine like someone whistling, it's likely a single faulty diode. If the whine sounds like more than one person whistling in harmony, it's likely there's more than one faulty diode in the array. Either way, you need to replace the alternator. The faulty diode is leaking battery voltage to ground and the battery is being slowly discharged, which in turn will show up at starting time after sitting for a while.

To save yourself some time, go by one of the auto parts chains and have them give you the free alternator check. If the problem is the usual diode array leakage, you have found the problem. You can depend on the premium grade of replacement at most of these places.

By the way, one of the 2011 Tahoes in our family has had the alternator replaced this summer due to a bad diode array, and the 2008 Denali has had two replaced in 160K miles. All our vehicles have UHF mobile radios, and those have become our finest early diagnostic warning tools.
 
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jluisi86

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I have been doing as many tests as i can and everything is pointing to the alternator. I did a temp. install with the radio and i have no noise so that rules out the radio itself. To my surprise, alternators arent that much for these trucks.
 
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