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2012 Tahoe PPV lowband noise

This forum is dedicated to helping people with questions about installing radio equipment in vehicles. This can include antenna installs, electrical wiring questions/problems, and mounting systems. Pictures of installs are welcome.

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Pj
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2012 Tahoe PPV lowband noise

Postby Pj » Mon Jul 04, 2016 8:51 am

I have a 2012 PPV Tahoe with a lip mount lowband antenna. Somewhere under the hood RFI from the charging system is getting into th antenna line. I can't figure out where though. Not sure if this is a common Tahoe issue or what I've missed in checking connections.

Removing the antenna and the noise goes away. Touch th center contact on the nmo and its back. Moved from the drivers side and to the passenger side same issue.

No RFI noted for any of the roof mount antennas or scanner.

Dual battery system, using OEM power for all installed equipment.
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Re: 2012 Tahoe PPV lowband noise

Postby Jim202 » Mon Jul 04, 2016 4:18 pm

Pj wrote:I have a 2012 PPV Tahoe with a lip mount lowband antenna. Somewhere under the hood RFI from the charging system is getting into th antenna line. I can't figure out where though. Not sure if this is a common Tahoe issue or what I've missed in checking connections.

Removing the antenna and the noise goes away. Touch th center contact on the nmo and its back. Moved from the drivers side and to the passenger side same issue.

No RFI noted for any of the roof mount antennas or scanner.

Dual battery system, using OEM power for all installed equipment.


Have you tried to ground the hood to the body of the vehicle? Otherwise it's nothing more than a large antenna. Probably someplace in the area of a low band frequency.

You haven't exactly given any hints as to what the noise sounds like.

Is it a steady noise regardless of the engine speed?

Is it just a hash type noise, or is there a pulse type noise your talking about?

Are you hearing a whine that changes with engine speed? If so, does it change when you turn on your headlights?

Do you hear the noise when you first turn on the ignition before cranking the engine?

Some hints might help the group on here point you in the direction of solving your noise. There have been issues in the past where the exhaust pipe had to be grounded in several places to eliminate noise. Haven't seen anyone talk about this in a number of years. You might even try putting a small antenna on a long piece of coax cable connected to your radio and go sniffing around to see if you can localize the noise area.

Let the group here know what you find.

Jim

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Re: 2012 Tahoe PPV lowband noise

Postby Pj » Mon Jul 04, 2016 5:00 pm

I went thru the usual suspects. General hash - and I believe only when the alternator is pushing a higher charge to the batteries (dual battery). Its not the normal alternator whine. When the batteries are topped off, it goes away. It does not change with engine speed.

Its defiantly under the hood, as it does not seem to be going thru the electrical system to the radios and the when swapped to the roof antennas, its not there under the same circumstances.
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Re: 2012 Tahoe PPV lowband noise

Postby Jim202 » Tue Jul 05, 2016 2:29 pm

Pj wrote:I went thru the usual suspects. General hash - and I believe only when the alternator is pushing a higher charge to the batteries (dual battery). Its not the normal alternator whine. When the batteries are topped off, it goes away. It does not change with engine speed.

Its defiantly under the hood, as it does not seem to be going thru the electrical system to the radios and the when swapped to the roof antennas, its not there under the same circumstances.


Well if you think it might be from the alternator, lets go the next step. By the way, I have 2004 Ford F250 diesel and have replace the alternator 3 times since I bought the truck new.

Take a digital volt meter and measure the battery voltage before you start the engine in the morning. Write it down for each of the steps.

Start the engine with all the vehicle items shut off. This means the air conditioner and all that kind of stuff. Measure the voltage.

Now turn on the headlights on low beam. Measure the voltage.

Now put the headlights on high beam. Measure the voltage.

At this point I want you to measure the voltage between the negative on the battery and the actual engine metal. It will be a low voltage like in the milli volt rang if the normal vehicle connections are good.

Lets continue and turn on the heater, not the air conditioner with the fan on high. Measure the voltage at the battery terminals.

Now change from heat to the air conditioner with the fan on high. Measure the battery voltage.

With the air conditioner on high, turn on the windshield wipers on high. Measure the battery voltage.

Now shut everything down and lets discuss what the reading show. What you will see is a point where the battery voltage no longer stayed at the 13.5 to 14.0 or so voltage. This is all going on the assumption that the engine is idling at the correct speed. I would guess that this idle RPM would be around 650 to 700 RPM. If the RPM is low, this would also be a problem.

Anyway, the intent of this load test is to see if it is putting out the required current to carry the vehicle load. If the diode stack in the alternator is bad, you won't get the rated current and the voltage will drop as the load is increased.

One step I didn't mention is to also measure the AC voltage at each of the above steps. It means a constant changing of the meter setting. Even I mess up when doing this test. So go slow and make sure you know which position your meter is in when making all the measurements.

Before I forget to mention it, the AC voltage you measure will be very low. Like in the low AC millivolts. If you start to see a high AC reading of like 200 or more millivolts, I would start to suspect a bad diode in the alternator.

This might seem like a long multi step process to decide if your alternator is good or bad. But it does point the finger.

Another comment I will make here, is if the battery is 3 years old or more, I don't want to hear any comments about why we went through the steps above. As auto batteries age, the internal resistance goes up and the noise filtering effect the battery supplies starts to go away. At some point you will find the battery failing you. The indications are the motor is turning over slower than normal. The dash clock radio is loosing time or resets to 12:00 when you start the engine. These are all indications that your battery is headed out the door. Hot weather kills batteries and real cold weather shows the batteries that are almost dead.

Let the group here know how you made out with your noise problem.

Jim

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Re: 2012 Tahoe PPV lowband noise

Postby giguchan » Sat Jul 16, 2016 2:26 pm

Jim,
Thanks for that information... I will be printing this out and keeping for future reference. I've always wanted a Tahoe.
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