Radio antenna help

[Shdwdrgn]

I've been having trouble with reception for the past couple years, but generally it has been fine for my morning drive so I wasn't too worried about it. Last week the reception dropped out almost completely. I can pick up stations in some places (like my driveway), but I'm pretty much dead on the road. I tore my dash apart yesterday to check the antenna as this is the most probable cause and I assumed that because of the sudden drop, the antenna had simply come unplugged from the radio. Unfortunately this was not the case. In fact the antenna cable was in so tight that I had to use some needlenose to give the plug a gentle nudge. So my next thought was corrosion. I cleaned up the plug a bit, and it seemed to improve the reception in the driveway, but on my way to work this morning I couldn't get enough signal to bother keeping the radio on. While I had the dash apart, I also inspected what I could see of the antenna cable... There were no hard kinks or any signs of rubbing. The protective foam was still intact around it. The only thing I can think of is that when the radio is pushed back into the dash, it is bending the cable enough that it loses connectivity from the plug?

I live about 30 miles from Denver, and all the stations have their antennas sitting up on the side of the mountain. I practically have line-of-sight to their antennas during my entire drive, so I would think I could pick up a signal from here with a paperclip... So what's going on? Any suggestions on what else I can easily check? Would it be of any use to put a multimeter across the antenna plug, and if so what readings should I see? If I can determine from readings that the plug is the culprit, is there any place that can cheaply crimp a new plug on the wire (and by 'cheap' I mean less than the cost of buying my own pair of crimps)? If nothing else, I may just have to run to Radio Shack and pick up another antenna to test out.

 

[ddgm]

The easiest thing is what you said. Pick up another antenna to test.

 

[Texan]

The antenna mast threads onto the mount on the outside. Could it be corroded?

 

[djthumper]

Did you ever think that it could be your receiver?

 

[Shdwdrgn]

The antenna mast threads onto the mount on the outside. Could it be corroded?

Hmm that's a good idea... I'll grab a wrench and unscrew it tonight to have a look.

Did you ever think that it could be your receiver?

No, say it isn't so! I have the 6-disc player, is this a common problem (not that I've ever seen it reported before)? It probably wouldn't hurt to open it up and have a look at the internal antenna connection. It keeps freaking out on disc #3 anyway, so I should probably clean it out. Any thoughts on what I might look for?

 

[djthumper]

If you use a multi-meter to test the antenna you should have about 75 ohms of resistance. If not there is a chance that your coax is bad. If you test the radio side you can only test for continuity, you may need an adapter to do that. Other than if you have another antenna on hand to test the receiver there is no really good way, unless you have access to a service monitor to inject the signal to the radio.

 

[coolasice]

Does it have the antenna in the fender or rear window? Rear window unit has special switch module for am/fm

I believe there is also a splice just behind the glovebox also, may want to check there.

 

[Shdwdrgn]

@coolasice - I have the antenna in the front fender. Would there still be a splice?

 

[coolasice]

Yes, behind the glove box

 

[Shdwdrgn]

Good deal, I can look for that tonight as well. Have to drop off my ballot after work so I won't have time to tear into the dash yet, but at least I have several things to check on when I do get the time. I might also try simply sticking a length of wire into the radio jack as well, and see if it picks up anything that way. I'm having trouble with the idea that a coax cable could fail in steps, which makes me lean more towards a corrosion issue, but we'll see.

 

[coolasice]

If the coax rubbed through to the center and grounds out it would cause no reception

 

[coolasice]

Also see tsb http://workshop-manuals.com/chevrolet/trailblazer_4wd/v8-5.3l_vin_m/accessories_and_optional_equipment/antenna/antenna_radio/antenna_cable/component_information/technical_service_bulletins/customer_interest_for_antenna_cable/05-08-44-016a/mar/06/audio_system_poor_radio_reception/station_drifting/

 

[Shdwdrgn]

If the coax rubbed through to the center and grounds out it would cause no reception

I agree... but if that were the case I would expect the antenna to not work at all, similar to being unplugged. The coax should either work, or not work. It shouldn't just suddenly degrade the signal in obvious steps. That's the part that I can't figure out.

 

[coolasice]

direct from the service manual:
Radio Poor Reception
Diagnostic System Check - Entertainment System
Always perform the Entertainment System Diagnostic System Check before proceeding with these diagnostic procedures. Refer to Diagnostic System Check - Entertainment System .
Using a Test Antenna
Use a test mast antenna to quickly check for poor vehicle antenna operation. Unplug antenna lead-in connector from radio receiver and plug a test antenna into radio. Make sure the test antenna base is grounded to the vehicle chassis and keep hands off the mast. Check radio reception in an area away from electrical interferences. Tune to several weak and strong AM and FM stations. If the radio reception improved, the problem exists with the vehicle antenna and/or lead-in cable. If the reception is still poor, refer to Audio System Troubleshooting Hints .
Antenna Ground Test
Important: Always zero out the DMM before taking a resistance measurement in order to ensure an accurate reading.
• Base of the antenna for a poor connection to body ground.
• 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 in Wiring Systems.

1. Disconnect the negative battery cable.
2. Disconnect the antenna lead-in connector from the radio receiver.
3. Measure the resistance from the negative battery cable to the coaxial cable, outer conductor, connector.
4. The resistance measured should be 0.20 ohms or less.
5. Test the following when the resistance is greater than 0.20 ohms.
6. After finding and correcting the condition, operate the system in order to verify the repair.

Antenna Coaxial Cable Testing
Use the appropriate chart and diagram to test the antenna coaxial cable resistances for the antenna system on the vehicle. Refer to the table when testing the antenna and/or lead-in cable.
Mast Antenna System


(1) Negative Battery Cable (2) Coaxial Cable Conductor - Radio End (3) Coaxial Cable Metal Outer Shield - Radio End (4) Coaxial Cable Metal Outer Shield - Antenna End (5) Coaxial Cable Conductor - Antenna End (6) Antenna Base (7) Antenna Mast (8) Antenna Coaxial Cable
Ohmmeter Probes At Points
Resistance Measured In Ohms
1 and 3
Less than 0.2
1 and 4
Less than 0.2
1 and 6
Less than 0.2
1 and 2
Infinite
1 and 5
Infinite
1 and 7
Infinite
2 and 3
Infinite
2 and 4
Infinite
2 and 6
Infinite
3 and 4
Less than 0.2
3 and 6
Less than 0.2
3 and 5
Infinite
3 and 7
Infinite
Important: Always zero out the DMM before taking a resistance measurement in order to ensure an accurate reading.
• RG-58/RG-59 type cable -- less than 0.20 ohms per foot
• RG-62/RG-62M type cable -- less than 3.5 ohms per foot

1. Measure the resistance from the coax center conductor to antenna mast, ohmmeter probes at points 2 and 7.
2. Total resistance from end to end of center conductor-ohmmeter probes at points 2 and 5:
3. When checking the resistance, cautiously wiggle the lead-in tip and cable. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
4. Replace the antenna and/or lead-in cable when the above readings are not obtained.

 

[Shdwdrgn]

OK first off... thanks for posting that info, great to have that in the forum!

Second... holy crap that's convinient -- You can reach the back of the radio right through the glove box hole? I never even considered it until I opened it up!

And last -- the problem is definitely in the crimped plug that goes into the radio. I measured around 700 ohms, and it goes as high as 1300 as I move the plug around. I pushed the plug back into the radio turned around against the direction the cable was previously bent, and had a station pop in that I wasn't getting before. So thanks to everyone with all the suggestions, I can finally get this fixed!

I'm guessing with all the slack cable, I could easily cut it back an inch or two from the stock plug and crimp on a new plug. I wonder if this is a standard plug that I can pick up from any car-parts store? I'll have to look around and see who carries the parts...

 

[coolasice]

OK first off... thanks for posting that info, great to have that in the forum!

Second... holy crap that's convinient -- You can reach the back of the radio right through the glove box hole? I never even considered it until I opened it up!

And last -- the problem is definitely in the crimped plug that goes into the radio. I measured around 700 ohms, and it goes as high as 1300 as I move the plug around. I pushed the plug back into the radio turned around against the direction the cable was previously bent, and had a station pop in that I wasn't getting before. So thanks to everyone with all the suggestions, I can finally get this fixed!

I'm guessing with all the slack cable, I could easily cut it back an inch or two from the stock plug and crimp on a new plug. I wonder if this is a standard plug that I can pick up from any car-parts store? I'll have to look around and see who carries the parts...

Never seen just the plugs available, best choice would be a yard or dealer... But replacing that short cable may be more difficult then it looks.

 

[BlazingTrails]

You used to be able to buy the cable ends at radio shack. Online maybe?

 

[Shdwdrgn]

I've been searching around the last couple days... Unfortunately some dimwit at GM decided to use a non-standard plug, so I've had no luck finding a replacement. I don't suppose anyone has ever found a part or model number for this plug?

 

[BlazingTrails]

Here is a possible solution

Adapter to Stock Radio

And then you can get this for your cable.

Male End

 

[Shdwdrgn]

@BlazingTrails -- I was just looking at exactly that over on Amazon. I've been contemplating getting an android-powered head unit, so changing my antenna to a standard plug isn't a concern. "Gm Micro/Delco" seems to be the correct identifier for the plug, but I haven't had any luck finding the conector by itself. One thing I like about this pigtail is the solid metal 90-degree elbow -- that should go a long way towards preventing a repeat problem.

So I'll get one of these ordered tonight and see how it looks when it gets here.

 

[coolasice]

or... http://www.amazon.com/ACDelco-25893238-Original-Equipment-Extension/dp/B0049ZB4QQ
for a direct replacement

 

[BlazingTrails]

or... http://www.amazon.com/ACDelco-25893238-Original-Equipment-Extension/dp/B0049ZB4QQ
for a direct replacement

Looking for something?
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Go to Amazon.com's Home Page

 

[coolasice]

Looking for something?
We're sorry. The Web address you entered is not a functioning page on our site

Go to Amazon.com's Home Page

fixed

 

[Shdwdrgn]

Looks like I never came back to update this thread... but so far I've had no luck.

I got the adapters in and picked up a standard tip from radio shack. Got the new tip put on, and reception was only marginally better. I put my meter across the new tip, and measured infinity, making me believe the antenna wire is broken further up.

Yesterday I picked up a cheap aftermarket antenna, plugged it in, and laid it up on my dash. On my drive in to work this morning, I find that I still have no decent reception. Even holding the antenna up outside the door, I still can't get in some stations that should be easy to pick up. I'm starting to think the problem may be in my radio rather than the antenna... any thoughts on how I could test this?

 

[Shdwdrgn]

Well that didn't last long... the radio has been really bad again through the weekend, so I thought I would pull things apart and try to clean the connectors. The damn pigtail fell apart at the the GM tip. I'll have to clean it up and see if I can re-solder and crimp the connector, but this is getting rather irritating...

 

[BlazingTrails]

Dang man, I hate that it is giving you such a hard time. I would fix it for you if you were close by.....

 

[Shdwdrgn]

Well if I can get a good connection re-using the existing plug, I'm debating either taping or shrink-wrapping the end to give it more strength, but honestly I don't know what the issue is. This pigtail has a metal-braced 90-degree end, and there's a couple feet of extra antenna cable tucked in the glove box from the aftermarket antenna, so there's no reason there should have been any strain on the plug. However I don't think logic is playing any part in this drama, so I'll just chalk it up to this being a really crappy Monday (still).