OnStar and radio problem.

[Phil P2]

OnStar and radio problem.

 

I have a problem with the AM portion of the radio in my 2009 3500 HD.

 

The radio seems to work on AM for a while and then it just suddenly stops receiving the station and I get a loud static noise. It seems to happen when I use the OnStar system to communicate. But not every time.

 

If I drive the truck closer to the station transmitter it will receive OK. Drive further away and the reception stops and the noise starts again.

 

The dealer checked it and said they couldn’t duplicate the problem. When I got in the truck the radio was tuned to the locale AM station whose transmitter is across the street from the dealer.

 

I ask for the technician to come to the truck and I demonstrated that the only station the AM portion would receive was the local station that is across the street from the dealer.

 

I made the statement that it acted like the AM antenna wasn’t connected to the radio.

 

The technician explained to me that unlike FM the AM didn’t require and antenna.

 

So I need to find a dealer that has a technician that knows some thing about RF.

 

My question is where is the AM antenna located on the 2009 4 door Silverado 3500 HD Duramax?

 

My next question is what does GM do about the feedback to the AM & FM receiver that would happen when you use the OnStar to communicate with an OnStar operator?

 

Thanks

 

Phil P

[MikeNH]

There is only one antenna to the best of my knowledge and that is the mast antenna outside the truck. Feedback should be a non-issue as the radio is supposed to mute when OnStar is being used.

[Phil P2]

Hi

 

Thanks for the information.

 

Thanks for the information. Dou you know for sure that there is only one antenna for both the AM & FM receivers. It is a fact that they both need an antenna but they are in the same band of frequencies so it would be acceptable to use the same antenna.

 

The XM antenna is incorporated with the OnStar antenna system.

 

I had the thought that my use of the term feed back would be interpreted as audio feed back.

 

This is not what I am referring to. When a transmitter radiates RF when it is used to uplink to OnStar the RF the receivers for the other 3 radios XM, FM, and AM would be damaged by the RF unless the antenna input to these receivers is shunted or blocked in some way. The common way is to use tuned cavities that will only allow a very narrow “window” for RF and these cavities are “tuned” to the input frequency of the receiver being protected. The second way is to shunt the antenna to ground with a switching transistor or relay.

 

My question is what is GM using to protect the receivers from damage by RF radiation?

 

Phil P

[GMCustomerService]

Phil,

 

I can also look into this for you on my end with the last eight of your VIN. Contact me privately for more assistance. Thank you.

 

Tricia, GM Customer Service.

[MikeNH]

Phil, it sounds as though you know far more than I do about radios but I know for sure there is one "radio" antenna input on the deck and that cable goes directly to the mast outside. As for RF shielding, I don't see how OnStar or XM in these would be any different than aftermarket options (aka your cell phone) and I know for sure those sorts of things are considered when designing radios and such. But that's about the end of my knowledge of such things.

 

 

Sent from my iPhone using Tapatalk

[Phil P2]

Phil, it sounds as though you know far more than I do about radios but I know for sure there is one "radio" antenna input on the deck and that cable goes directly to the mast outside. As for RF shielding, I don't see how OnStar or XM in these would be any different than aftermarket options (aka your cell phone) and I know for sure those sorts of things are considered when designing radios and such. But that's about the end of my knowledge of such things.

 

 

Sent from my iPhone using Tapatalk

 

 

Hello MikeNH

 

I have electronics background but I haven’t had any recurrent training for many years. I was the guy that decided if the radio black box or some thing in the aircraft was causing the problem. All of this while you waited at the gate to see if the airline could get the “mechanical” delay problem cleared so you could ride in the aircraft.

 

However if you place your cell phone near the antenna of your FM or AM radio you will hear it “pulse” thru the speakers. This is the cell phone “pinging” the nearest cell tower so the tower knows where the phone is.

 

There are 2 antennas that I can identify on the truck. One is a standard “stick” mounted on the right fender just a littler forward of the passenger door. This could be used for both FM and AM receivers. The other is the OnStar/XM antenna and that is the blade on the roof of the cab. There is a dark flowered border all the way around the windshield. In older automobiles this was the AM antenna.

 

The OnStar transmitter has to be in the area of 5 watts output to work the way it does. The cell phone power is only between 20 millliwatts and 250 miliwatts depending on the distance from the cell tower. The equipment in the tower controls the power output of the phone. The OnStar/XM antenna being co-located must have some kind of protection for the XM/Onstar receiver during the time the transmitter is active. I am convinced that there is some kind of protection for the AM/FM radio receiver as well.

 

I am also am amateur radio operator and have built and configured amateur “repeaters” that transmit and receive at the same time. They require a “cavity” that can be tuned to only pass the receivers frequency to the receiver and the other one tuned to pass only the frequency the transmitter is transmitting on. These cavities are way to large to be used in the OnStar system.

 

Phil P

[MikeNH]

I put "radio" in quotes to try and mean that there is only one antenna used for the traditional AM/FM radio. I was posting from the phone and trying to be brief, sorry for the confusion.

 

I haven't heard the pulse you describe with anything but true Nextel phones (ie the rare models that still exclusively use the iDEN network). The mast antenna is the only antenna going to the radio, I have checked schematics to verify this. GM trucks do not use the glass as any sort of antenna (in the past I have seen this but it is usually the rear glass or rear side glass on SUVs). The plastic deal on the roof is indeed the XM/OnStar antenna. I am not totally sure where the XM tuner lives but I know for sure the OS module is a separate unit that lives on it's own somewhere else in the dash, the cell signal is not piped into the radio. I don't know what GM does for shielding but I do know the OnStar module is rather robust (likely to try and withstand crashes) and distance from the radio likely does something but I doubt GM will tell you what they do in terms of details.

[wottenad]

Although I don't know what the theoretical causes of this problem may be, my 36 years as a car audio installer tells me that you probably have a poor (or intermittently poor) ground at the antenna or a bad cable leading into the radio. You may want to remove the antenna mast base and make sure that it's got a good ground, then check the short cable that jumps from the antenna lead to the radio - the joint for this is under the defroster trim on top of the dash on the passenger side.

 

Easiest way to eliminate the issue is to replace the whole thing - it's about $30.

[Phil P2]

Thanks guys. The dealer is supposed to have someone that knows these radio installations. When the technician tells me that the AM portion doesn’t need an antenna then tell me I am looking at a $300 radio and $250 to program the computer to be compatible with the replacement radio I am hesitant to precede until I can fine a technician that under stands RF.

 

ADC Mobile if it was the antenna lead in or ground I should experience signal degradation on both AM and FM. This isn’t the case. This is whey I think there is something else involved. The RF (radiated frequency) gets in to the receiver thru the antenna. Any thing over 1 watt within 3 ft of the receiver antenna would or could damage the receive front end. I am sure there is some type of protection either a switching transistor that is grounding the antenna input lead inside the radio or a relay that opens the circuit or possibly 2 of these and the AM one is intermittent in its conductivity.

 

MikeNH If you don’t remember the late 60’s and early 70”s vehicles you wouldn’t remember the windshield antennas. They were a nice dipole antenna built into the lamination between the 2 glass pains of safety glass. They worked well but commonly were damage when the class was change for some reason then a fender antenna was installed.

 

The distance from the radio would not have a bearing on RF between the 2 antennas. It’s the distance between the antennas that would change the severity of the RF feed back into the radio front end. Your reference to the schematic indicates this is probably inside the radio “black” box. This requires an electronics repair lab to do anything with.

 

By the way the schematics you referred to are they contained in the Helm manuals that GM recommends if the owner wants to purchase manuals?

 

Thanks again guys it has been fun.

[MikeNH]

Thanks guys. The dealer is supposed to have someone that knows these radio installations. When the technician tells me that the AM portion doesn’t need an antenna then tell me I am looking at a $300 radio and $250 to program the computer to be compatible with the replacement radio I am hesitant to precede until I can fine a technician that under stands RF.

 

ADC Mobile if it was the antenna lead in or ground I should experience signal degradation on both AM and FM. This isn’t the case. This is whey I think there is something else involved. The RF (radiated frequency) gets in to the receiver thru the antenna. Any thing over 1 watt within 3 ft of the receiver antenna would or could damage the receive front end. I am sure there is some type of protection either a switching transistor that is grounding the antenna input lead inside the radio or a relay that opens the circuit or possibly 2 of these and the AM one is intermittent in its conductivity.

 

MikeNH If you don’t remember the late 60’s and early 70”s vehicles you wouldn’t remember the windshield antennas. They were a nice dipole antenna built into the lamination between the 2 glass pains of safety glass. They worked well but commonly were damage when the class was change for some reason then a fender antenna was installed.

 

The distance from the radio would not have a bearing on RF between the 2 antennas. It’s the distance between the antennas that would change the severity of the RF feed back into the radio front end. Your reference to the schematic indicates this is probably inside the radio “black” box. This requires an electronics repair lab to do anything with.

 

By the way the schematics you referred to are they contained in the Helm manuals that GM recommends if the owner wants to purchase manuals?

 

Thanks again guys it has been fun.

 

 

 

Phil I've seen what you describe but unfortunately I don't remember the 60s or the 70s- I wasn't born until 1984.

 

As for schematics, I've bought AllData subscriptions for every vehicle I've owned the past 8 years or so (that's 4- I had trouble keeping them for a while ). They have TSBs, manuals, wiring schematics all for a decent price.

[Phil P2]

Hi

 

When I first posted here I ordered the repair manuals for this truck from Helm.

 

These manuals are a set of 7 volumes. They have detailed descriptions on how the systems work including the OnStar and all associated “black boxes”. After reading for about an hour and studying the wiring schematics I now know more about this system than I ever wanted to.

 

The OnStar module mutes the transmitted signal inside the OnStar box so the XM and OnStar receivers are isolated from their antenna and at the same time sends a signal on 2 separate wires to the radio that mutes the audio and isolates the Antenna system. There is only one antenna for the AM / FM receivers and one for the XM radio receivers.

 

I will now have to find a dealer that has a technician that has at least read the book. The technician at the dealer I am doing business with hasn’t read the book or he wouldn’t have made the statement several times that the AM radio didn’t need an antenna because of the frequency it used.

 

How ever the new radio will need to be programmed with the vehicles VIN number before it will work. I don’t see where this should cost $250. I will now spend the time to see what kind of software they use to do this programming. The data interface is common to most all Windows based computers.

 

Thanks a lot you all it has been fun.

 

Phil P

[00Silverado4x4]

Windshield antennas, I remember those...oh crap I just dated myself...lol

[MikeNH]

Unless you're an electrical ninja, you'll have a tough time making some 3rd party software work to reprogram a radio. Any programming is done with the GM Tech II scan tool as far as I know.

[Phil P2]

Hi

 

I have the scan tool its just not up to date. I had to help when GM produced a bunch of 5500’s with bad connectors to the computer bank. That computer bank (5 if I remember correctly) was mounted all in a row on the engine side of the boot cowl. LOL

 

By the way that scan tool is Windows based.

 

Phil P