I have been reading through the FAQ section and I am confused about getting power to the antenna module in a C6. I am planning on installing a pioneer f700bt in my 08 vert using the GMAH24 interface. If you replace the factory head unit how do you send the on signal to the module? Is it even necessary?

I do see where some people used the blue wire on the GMAH24 but the wiring diagram shows N/A as the signal. I am confused.

 

This post is the key:

http://forums.corvetteforum.com/show...1&postcount=10

Use the power antenna trigger from the radio, get a voltage regulator at Radio Shack to step 12V down to 5V and tie that wire off to B3(white) in the factory 24 wire harness and you should be all set.

 

Thanks, I will give that a try.

I have another issue I am trying to figure out. I have everything plugged in for a test run; everything seems to work. I get a pop through the speakers when exiting on star or opening the car door after shutting the car off (the retained accessory power function).

 

I am not sure that I understand this. In the service manual schematic it shows an antenna enable signal from the radio that splits at splice 204 and goes to the amp and the antenna module. If the amp is powered up then the antenna module should be also. So is the yellow FM composite signal wire that needs the 5V that they are talking about?

 

I don't have the diagram in front of me so it's hard to address the question specfically. But one thing I can answer is no, just because the amp's on doesn't mean the antenna module is. I believe it only switches on when you select radio as the input. Applying 5V to that wire does work.

 

Thanks. I checked with a fluke. The white wire has 12V when the factory radio is plugged all the time; this signal goes to the amp also. The yellow wire that goes to the ant module has 6.12 volts on it with the factory radio plugged in and the ant module hooked up (8 volts if the wire is disconnected from the ant module) and no AM selected, with AM selected there is no voltage. My confusion was from the other post that stated that they hooked up 5V to the white wire which is B3; I think it should have been the yellow wire which is A4. So I think you need both of these signals for it to work correctly.

I really don't plan on listening to the AM/FM much this is more for my understanding. I really appreciate the help.

 

on every c6 ive one done a radio/navi in ive never had an issue with any of this stuff, then again on the c5s it was a 50/50 roll for me

 

Ok, I'm in the middle of installing a car computer and ran into the issue of no radio reception with the stock antenna as well. I now know why.

It's clear you need a trigger on the ant. enable wire (B3-White) of the radio harness but where did the 5v value come from if silverstreak is measuring 12v at that lead? But also mentioned in the post is the yellow, A4 wire which is the FM composite signal wire. Does this also need powering? If so, what voltage? Is this signal coming from or going to the radio?

What I'm gathering from the Fluke readings is this: B3, ant enable is the power line to the antenna module which seems like it is 12v since there is no connection in the schematic that shows a 12v supply. It has been measured as a 12v rail when the radio is turned on. There is, however, a ground drawn on the antenna module schematic. When the FM composite signal is measured, it shows 8v removed from the circuit, around 6v with the FM selected but 0v when the AM is selected. This is how I am interpreting this data:

B3 is the actual power to the antenna module, it is 12v. A4 is a second voltage used to trigger the right and left antenna modules to combine their anntenna signals and that composite signal is sent back to the radio. This would explain the 6v when the FM channel is selected and the 0v when the AM is selected: You only need the use of one antenna for AM. You get a reading of 8v on that line when the connector is disconnected due to the fact you are removing that from the antenna module, whos circuit is causing a voltage drop.

From this conclusion I think the proper way to utilize the antenna is to power B3 with 12v and A4 with 8v but only when listening to the FM station. Not sure if leaving that powered for the AM has any ill affect on the AM signal or if its done that way for power reasons.

Any thoughts?

Jay

 

Ok, to put this issue to rest once and for all, I finally found the section in the tech manuals that describe the full antenna function. It's in Vol. 3 page 11-90. In short, my description above is correct. The antenna enable signal is 12v or battery voltage. This is needed for both AM and FM signals to the radio. No enable signal/voltage, no reception.

Short version of how this system works. There are two antenna modules in the back of the car termed right and left. There are 3 antennas, 2 FM and 1 AM. In AM mode the Left antenna module takes the signal from the AM antenna, amplifies it and sends it back to the radio via the coax antenna cable. For the FM, the radio sends the antenna enable signal at 12v plus the FM composite signal that is 5-8v. The Left antenna module sends the 8v FM composite signal to the right antenna module where is takes the signal from the right FM antenna (FM2) and sends it to the Left antenna module. The Left antenna module then takes the signal from its antenna (FM1) and combines it with the FM2 signal, amplifies it and sends it to the radio.

That's basically how it works. There is one other thing the manual states and that is the factory radio uses the FM composite signal as a feedback to the Left antenna module to indicate the quality of the signal. Hence the allowable voltage of 5-8v. Not sure if making it 8v constant vs. 5v constant would make it a better signal. I suspect a 5v constant would tell the module the signal is not that great and it would keep trying to boost it where as 8v would tell it it's a good signal, don't boost it. I suspect if the 8v signal applied as an aftermarket fix didn't work, one could wire in a small potentiometer with one lead at 8v and the other lead open with a resistance selected that would never give you less than 5v. You could then adjust the FM composite signal voltage to tell the Left antenna module to boost the signal in poor reception areas.

Jay

 

I'd recommend adding this to the C6 audio FAQ. <del>Crease-guard's advice above is right on.

The only thing I'll add is that it took at least 6v on the yellow (A4 "FM Composite") wire for me to get a stable FM signal. At 5v the signal would cycle in and out. </del>

...see below for update...

 

Then that pretty much confirms my suspicion about the composite signal voltage. I wired up a circuit and pot with a voltage reg to allow the 5-8v adjustment range by hand in case I get in an area with bad signals.

Curious about the AM signal. Are you still getting good AM reception with the composite signal voltage (6v) AND the antenna module voltage (12v) at the same time? From what I gather in the stock units, the FM composite signal voltage cuts out when the AM band is selected. I wired my pot up to a switch to be able to turn off the composite signal when on AM.

Jay

 

My AM reception is the same as before, but I think that is because the head unit has an internal AM antenna.

 

I have to call BS on this myself before anyone else wastes their time. I was apparently wrong.

Although the reception initially appeared to improve on the "weak" station I used to test the "signal boost" from the above procedure, over time it has degraded and become worse. There is also a cyclical static noise that is added to the signal at some point after the radio is powered on (this could be from the change in time or vehicle position, I'm not sure). I now believe my initial perceived improvement was due to some external factor, possibly related to weather/cloud cover.

I've tried changing the voltage on the yellow "FM Composite" wire, between 4 and 10 volts, and in each case the cyclical static noise reappeared after some time. Thus, I believe there is more to this FM composite signal sent by the factory head units than mere voltage.

The good news, however, is that with zero volts on the FM composite wire, both FM antennas ARE WORKING, as is the AM antenna. I've tested this by unplugging the antennas from the modules in the rear of the car while the radio is on. The radio still receives FM stations with either of the antennas unplugged, but nothing when both are unplugged. The radio's AM signal goes completely dead when the driver's side antenna (actually a plug with 2 antenna wires, AM and FM) is unplugged.

My GUESS is that the FM composite wire is part of some sort of feedback system that helps the main antenna module decide which FM antenna (left or right) has the better signal for the station currently being tuned. The main module probably alternates between the 2 antennas when it sees some sort of condition (maybe "static") on the composite wire, looking for that condition to go away. This constant switching is probably what caused my cyclical static noise.

Bottom line, unless we can determine what "protocol" is used on the FM composite wire, it is best to just leave it disconnected.

 

Well the manual states it does work as a feedback system so you are correct at that.

This is good stuff. I will probably not use an adjustable system for the antenna and simply leave the composite signal floating.

Jay

 

In C5's the antenna module simply combines and amplifies the signal from the two window antennas. The module is powered by the same 12v that powers up the bose amps, but is turned on (when needed) by a 5v signal sent out by the radio. Click here for a thread that shows how that was determined, and here for the plug pin-out of the C5 coupe antenna module (no schematics avail for that).

It appears to be different in C6's. Click here for the C6 antennas schematic.

It looks to me like the C6 module is both powered AND turned on by the 12v signal sent out on B3 (amp turn on power), but then the 'FM Composit Signal' somehow fine tunes the amplification.

I currently have an aftermarket HU playing through the stock amps (AVIC-D3). When I installed it I was wondering if the C6 had the same 5v antenna trigger as my old C5 did, but the fact that the only possible wire to hook it up to was called 'FM Composit Signal' instead of 'Radio Signal On' concerned me, so I just left the 12v on it's own. My reception is just as good, if not better, with the new HU as it was with the OEM radio. If the reception sucked, I would have reconnected the radio to see if I could figure out how the feedback circuit worked so i could use it, but I didn't feel the need.

I'm in the process of building an amp rack/sub box so I can eliminate everything bose from my system. During the conversion my plan is to leave the bose amp in place, but pull the #31 AMP fuse, and connect my HU 'antenna turn on' wire to the white B3 wire (currently connected to HU 'amp turn on' wire) so that the antenna is only powered when I'm listening to the radio.

HTH

 

So....What if anything are you supplying to the modules?

Judd

 

12v on the white wire at B3 of the main radio connector.

FYI, this will also supply the stock amp if you haven't removed it. Pull AMP fuse 31 to remove the constant 12v from the bose amp.