carbuff

Ok, for the next installment in my DNX7100 questions...

I pulled the head unit back out this morning to connect the missing XM antenna wire, and I checked over the rest of my connections. One thing that's been bugging me this week is the radio reception, particularly the AM reception.

AM is pretty much useless. I have a handful of stations that I regularly listened to with the stock head unit, but I can barely tune them in, if at all.

Has anyone else with this unit, or heck, any aftermarket unit, noticed poor AM reception?

bogus

I have not seen a good AM tuner in years... except OEM.

I don't know how to help... HD radio maybe? is it available in your area?

TheKomoman

There's an antenna amplifier in our cars because of the nature of the fibreglass bodies(you can't use them as antennas). When you install an aftermarket head you lose the trigger signal to turn this on. I don't listen to AM or FM these days so I never remember to mention this!

It is possible to setup a trigger to turn this amp on, but I don't recall how off the top of my head. Do some search-digging, probably have to choose archives at this point, and you should be able to find a couple of threads where guys have done this.

WHT

I don't know anything about the Corvette antenna amplifier, but found this discussion on another Nav Forum. Thought it might jog a few memories or ideas:

After I installed my Panasonic H.U. just after I got the car almost a year ago, I noticed I didn't have any AM reception. FM reception was OK, but not spectacular. I had read some posts about you need to run power to the Vibe's built in antenna amplifier. The stock radio feeds the 12V needed through the wiring harness that attaches to the rear of the radio, but aftermarket wiring harnesses don't have this lead. I don't listen to AM that much, so I didn't pay attention.

About a foot back from the end of the antenna lead that goes into the rear of your radio is a black wire that runs along the antenna lead. It then goes into a wiring harness with many other wires. Along this black wire is a white quick-disconnect that also has a piece of foam wrapped around it. I disconnected this white connector and cut back about 5 inches of the loosely fitting shrink-wrap type plastic that is around the wire. (to the left of the connector) (between the connector and where it meets the wiring harness) I then snipped the wire about 2 inches past the white connector so it would leave me enough wire to be able to strip the insulation and wire it into the 12V accessory (red) wire leading into the radio. You want to tap into the accessory lead, not the "always on" 12V lead.

I taped everything back up (including the other end that was cut, coming out of the wiring harness), plugged the connector back into the lead that runs along the antenna lead, and that's it.

Great FM and AM reception now!

Some radios have an output for a power antenna, Turn the radio on and the antenna goes up. If a radio had such a signal, couldn't it power the antenna amplifier?

Just installed an aftermarket Kenwood receiver - I ended up doing exactly what cohocarl did with the antenna power wire but I did have a "Power Antenna" lead from the HU wire harness that I used - I also checked with the techs at Crutchfield and they verified this was accurate as well. Either way, my reception is normal, if not better than the stock unit after doing this.

EDIT:

Markcz - In C5 coupes there is an antenna module/amplifier under the carpet behind the drivers seat. That module is what the front windshield and rear glass antenna leads connect to. From there it's a single antenna lead that plugs into the stock radio. Click here to see the schematic for the antenna module.

Here's my theory: The antenna module is normally powered by +12VDC supplied from the stock radio through the Dark Green wire, but it is TURNED ON with +5VDC through the Pink wire which is only energized when the stock radio is playing a radio station. Whenever an aftermarket HU is installed in a C5 the +12V Dark Green wire is connected to the new HU's 'antenna power out' wire, but the pink wire that actually turns on the antenna amplifier is never connected to a 5V source, which makes radio signal reception with an aftermarket HU just plain crappy.

I came up with that theory a few months ago when I installed my Kenwood HU. My radio reception is rather poor, however, between the MP3 CD player, Sirius channels 19 & 23, and my 60GB iPod with 14GB of music on it I just haven't been motivated enough to install my 5V power supply to see if it solves my reception problems. I bought a cell phone car charger that has a 5V output, one of these days I'll install it behind the seat by using the green wire at the module as the + source (it's connected to my Kenwood antenna power wire), the module ground wire as the ground, and then splice into the pink wire with the charger output. Theoretically that should give the module both 12V and 5V whenever my new HU is selected to the radio tuner, which theoretically should improve my radio reception.

carbuff

WHT,

Thanx for the information. I looked through the Service manuals today, and sure enough, there appears to be an output from the head unit to the antenna module to enable it. So, it seems I will be tearing into my dash again (I'm getting good at it now) and connect up the antenna output from the 7100 to the wire in the factory harness to drive this enable at the antenna module.

I'll report back here when I get this done and let you know how it went.

TheKomoman

Careful with that!!!! Any output from your head, like the power antenna lead, is going to be +12. The trigger that you tie off to for the antenna module needs to be dropped to +5V. There's an inexpensive voltage regulator you can buy at Radio Shack, but you need to be OK with soldering and you need to put it somewhere that it's heat can be disappated. All do-able, just stuff you need to keep in mind.

carbuff

Grumble... Thanx for the warning. The head unit almost certainly has 5V available inside, but perhaps not externally.

I'm able and willing to build a relay / voltage regulator circuit to do this if that's the necessary solution. Actually, I might be able to do it with just the VR and avoid the relay, but I need to think about that a little... Looks like another trip to Fry's at lunch today.

TheKomoman

IIRC the Kenwood only triggers the power antenna when you switch to the radio. So if you used the power antenna trigger as your source of +12 to regulate that should take care of it for you without a relay.

Mister Peebody

You recall correctly and !

carbuff

Ok... I just pulled everything back apart for a few small issues, and this was one of the tasks which I tackled. I can say that I now have a reasonably well-working antenna!

I went to my local Fry's to pick up a voltage regulator. The standard part number for these are 7805, but Fry's carried some other brand (NTE) I'd never heard of. The part number I used was an NTE960. This device converts voltage of up to 35V down to a regulated 5V.

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).

Before I finalized the connections, I powered up the radio and tried it out. It definitely made a difference, and the regulator was giving me a steady 5V when it should have.

So, thanx to those of you who pointed me in the right direction! Hopefully I'm done pulling my console/dash apart for a little while.

TheKomoman

Glad that worked for ya!

Thanks for detailing what you did, I added a link to your post to the FAQ.

MR.WaynesWorld

Will I need to do this on my C5??

SilverC54me

On C5 Coupes there is an antenna amp near the drivers lower seatbelt retractor. Verts and FRC/Z06 do not have this.

The antenna amp requires 12V to activate and has a 5v input for switching between front and rear antennas for FM only. That said in the LA, CA area I have only applied the 12v to the amp and am getting good reception.

There is a thread I will look for that goes into detail on this issue.

Gary

MR.WaynesWorld

Thanks Gary.... I looked at the wiring harness I got for the install and it actually has a amp turn on wire for the antenna amp, blue/white.

SilverC54me

Here is the link to the thread I mentioned.

http://forums.corvetteforum.com/show...ighlight=Radio

Gary

waddisme

I have a Z06, but my after market head unit AM reception in practically non-existent. FM is not much better. Is the amp somewhere else? I miss my AM radio.