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As many of you know, I ripped out the "Blose" Navi HU almost within the second year of ownership. While I LOVE the Kenwood Head Units for their Garmin Navi and overall great UI (user interface), I have always had problems with FM/AM reception. I upgraded my Kenwood DNX9140 to a DNX9980HD over the Summer hoping this would be resolved only to discover the same poor FM/AM.

So here's the scoop. C6 and C5's use electronic antennas which are triggered by the OEM radio. Of course I didn't know this nor did my installer. Could've save a few $'s. Enter the interweeb. I found this on another Corvette forum so in keeping with usage policy, here are the cut n' pastes.

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Quote:
Originally Posted by WB6HRO
The composite FM signal is most likely the sum of the two antennas, less prone to fading.

It is also known as Diversity Antenna System using more than one antenna.

Sometimes they polarize one antenna vertical and one horizontal.

The intent is to fill in areas that may flutter due to signal strenth.


This is correct. The service manuals spell out how this system works. Unfortunately, any aftermarket system won't give the FM composite signal. Our only solution would be to buy an aftermarket antenna or replicate the composite signal circuitry and algorithm used to fine tune the signal.
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Here is the one which helped out the most. Manny, I still owe you a traffic antenna.

Quote:
Originally Posted by TheKomoman
From the C6 Audio FAQ stickied at the top of the page:

Corvette Forum - View Single Post - DNX7100 - AM radio reception horrible...


This is some of the text from that link:

Quote:
The connections are easy, but you will have to solder them. The 7805 / 960 has 3 pins which are about 3/4" long. One is the input voltage, one is ground, and one is the regulated 5V output. I connected the 7100's power antenna control wire to the input, grounded the output, and connected the 5V output to the "Antenna Enable Signal" of the Antenna module. On my 05 C6, that was pin B3 of the 24-pin factory radio connector (it's a white wire, third one in on the 'bottom' of the connector).
The poster of that info may have had better reception after doing it, but that doesn't change the fact that the white wire at pin B3 of a C6 has 12v on it when the stock radio is installed. B3 is the 'amp turn on' wire for the stock C6 amp (in both Bose and non-Bose), it ALSO powers the antenna module, but it is definitely 12v. On the schematics that 12v circuit is called the 'antenna enable signal'.

===================================

If you go to the main body of the thread the above info was in, then follow the other links to the original thread that first mentions anything about 5v antenna circuits, you'll eventually end up at THIS THREAD.

That info was for a C5, but not even all C5's, just the coupe. C5 schematics are available HERE

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In a C6, the white wire at B3 is normally a 12v circuit, that I'm 100% sure of.

====================================

Since its raining out and I can't do my yardwork, I did some digging....

From the 2005 service manual:

Quote:
Radio Poor Reception
Schematic Reference: Radio/Audio System Schematics

Diagnostic System Check - Vehicle
Always perform the Diagnostic System Check - Vehicle before proceeding with these diagnostic procedures. Refer to Diagnostic System Check - Vehicle .

Antenna System Test
Important: Always zero out the DMM before taking a resistance measurement in order to ensure an accurate reading.


Disconnect the negative battery cable.
Disconnect the antenna lead-in connector from the radio receiver.
Measure the resistance from the negative battery cable to the coax outer conductor connector.
The resistance measured should be 0.20 ohms or less.
Test the following when the resistance is greater than 0.20 ohms. • The coaxial cable interconnects for a poor connection or corrosion.
• Test for an open or high resistance from the battery negative cable to the body. Refer to Circuit Testing and Wiring Repairs .

After finding and correcting the condition, operate the system in order to verify the repair.
Perform the Antenna Checking Procedures after confirming the integrity of the antenna ground.

Diversity Antenna System
This diversity antenna system is comprised of 3 antennas, 2 radio antenna modules, a coax, and an FM composite signal from the radio to the left antenna module. In AM and WX mode the system functions as follows: The left antenna module takes the signal from the AM antenna. The left antenna module amplifies this signal and sends it to the radio. In FM mode the system functions as follows: In this mode the radio supplies 5-8 volts over the FM composite signal wire and this switches the modules into FM mode. The left antenna module sends 8 volts to power the right antenna module via coax. The right antenna module takes signal from the FM2 antenna and sends it to the left antenna module where it is mixed with the signal from the FM1 antenna. The left antenna module combines and amplifies both signals and sends the combined signal to the radio. The FM composite signal also provides a feedback signal to the left antenna module, which indicates the quality of the signal. The following information lists the most probable cause of the concern to the least probable cause followed by the appropriate test for that condition. If the test leads to the replacement of a component, always inspect for a poor connection before proceeding with the replacement. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Perform the Antenna System Test and test the antenna coax cable prior to performing any of the following tests.


Poor Reception on Both AM and FM Bands

• The antenna enable circuit is open or shorted to ground or shorted to B+. Test for 8 volts on the antenna enable circuit at the left antenna module. If the voltage is not within or near the specified value, test the antenna enable circuit for an open or short to ground or short to B+. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
• The radio antenna modules are not grounded properly. The module grounding screws should be clean and tight. The antenna module grounds are either a chassis ground or a ground strap. Measure the resistance from the antenna module base plate to a good ground. Resistance should be 0.20 ohms or less. Find and correct the condition if the resistance is out of specification.
• The FM composite signal circuit to the radio antenna module is open, shorted to ground, or shorted to B+. Test the FM composite signal circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
• Defective left antenna module--Replace the left antenna module. Refer to Antenna Module Replacement for replacement.
• Defective left antenna--Replace the left antenna. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
• Defective coax between the left antenna module and the radio. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
• If no failures were found, replace the radio. Refer to Control Module References for replacement, setup, and programming.

Poor Reception on AM Band Only

• Defective left antenna module--Replace the left antenna module. Refer to Antenna Module Replacement for replacement.
• Defective AM antenna--Replace the antenna.
• The FM composite signal circuit to the radio antenna module is open, shorted to ground, or shorted to B+. Test the FM composite signal circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Poor Reception on FM Band Only

• Defective left antenna module, no 8-volt output--Replace the left antenna module. Refer to Antenna Module Replacement .
• Defective left or right antenna module--Replace the antenna module. Refer to Antenna Module Replacement .
• Defective FM1 or FM2 antenna--Replace the antenna.
• Defective coax between the left and right antenna modules--Refer to Circuit Testing and Wiring Repairs .
• The FM composite signal circuit to the radio antenna module is open, shorted to ground, or shorted to B+. Test the FM composite signal circuit at the left antenna module for 5-8 volts. If the voltage is not within or near the specified value, test the FM composite signal circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
• The coax between the left and right antenna modules is open or shorted to ground or short to B+. Test for 8 volts from the center conductor of the coax from the left antenna module. If the voltage is not within or near the specified value, test the coax for an open or short to ground or short to B+. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
====================================

Quote:
Originally Posted by Hawk07
So which is it? 12v as Mark says or 5v as MP35N says the FAQs calls for?

BOTH, but they need to be applied at the proper time and place
smash.gif


=====================================

For the best possible radio reception in a C6 with an aftermarket radio installed:

At the main C1 radio plug, supply 12v to the white wire at B3 whenever the radio is playing, and 5v to the yellow wire at A4 when you're listening to FM.


C6 schematics are available HERE

On the aftermarket interface adapters, the blue wire is at pin B3, so if you're still using the OEM amp/speaker setup your B3 wire already has 12v. If you're reception complaints are with AM, there's nothing more you can do. If FM is the problem, try adding the 5v at A4.

=============================

Just FYI, I have an AVIC-D3 installed in my '07 coupe. I have 12v on the white B3 wire whenever the HU is powered up, nothing is connected to my yellow A4 wire. My AM reception kinda sucks. My FM reception is pretty good. I almost never listen to local radio stations
crazy.gif


Anyone with other HU upgrade horror stories please share. Mine has been mostly resolved thanks to a 5VDC regulator to power the antenna and a very patient installer.
 
Last edited:
Manny@Dasilva

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Great post Pierre . Lots of very usefull info .

For me becuse I have a power antenna it should be no issue , just plug and play .

I will pick up the traffic antenna soon , hey makes a good excuse to drop in and visit with you and Bonnie :D
 
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Great post Pierre . Lots of very usefull info .

For me becuse I have a power antenna it should be no issue , just plug and play .

I will pick up the traffic antenna soon , hey makes a good excuse to drop in and visit with you and Bonnie :D
Mi casa e su casa mi amigo. Bring Carmi.

Pierre
 
S

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Great post Pierre . Lots of very usefull info .

For me becuse I have a power antenna it should be no issue , just plug and play .

I will pick up the traffic antenna soon , hey makes a good excuse to drop in and visit with you and Bonnie :D

Packaged up and getting posted tomorrow amigo. Padded envelope and all.

Pierre
 

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