Radio Reception
Thread Starter
Instructor
Joined: Jul 2003
Posts: 118
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From: Twin Lake Mi
Radio Reception
We have a 70 with an am-fm stereo radio. The am volume has to be maxed to hear anything & the fm does not seem to come in as well as it once did. I have tried trimming the am but don't see much difference. Would the ground plate & strap be a good place to start? How do I check the antenna wire itself? Thanks.
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
You can disconnect the antenna cable from the radio and use an ohnm meter to test the outside of the connector to ground, it should be near zero. Also the center pin to the antenna mast can be checked and it should be near zero. Check the ground plane to antenna mount connect, clean it up and verify the ground strap on the bottom of the antenna motor assy to the frame is good.
Racer
Joined: Jul 2004
Posts: 286
Likes: 1
From: Mesa az
The "technical" way to check a coax requires equipment that's a bit expensive and requires a bit of training as well. Far easier to just replace the cable and see if that fixes the problem. See if you can find one (a cable with antenna) that works and do a swap at the radio without actually installing it. You may have to attach the base of the antenna to the car's ground. If it does fix the problem, then go to the trouble of replacing yours.
Unless the cable has been damaged I'd have to guess the problem is more likely with the radio or external amplifier (I think there's an external one on '70s).
Unless the cable has been damaged I'd have to guess the problem is more likely with the radio or external amplifier (I think there's an external one on '70s).
Thread Starter
Instructor
Joined: Jul 2003
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From: Twin Lake Mi
I Think I may be headed in the right direction with the reception problem. I checked from the outside of the antenna connector that plugs into the radio to ground with an ohm meter & could not get a circuit. I pulled the ground plate, cleaned the ends of the ground strap on both sides & ends as well as the antenna end that fits into the ground plate. I did a temporay mickey mouse job of grounding & I have a circuit. It could be better but I have a new ground plate coming. I think once I clean the antenna ends better & put the new ground plate in, the reception will be a lot better. (I hope). I would also like to get some new screws & tangle washers to improve the connection at the ground plate & frame.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Maybe the antenna pin just fell out of the radio. It is in a Corvette and there may be just a teeennny bit of vibration every now and then.... (Remove the little cover panel on the front-right of the tranny tunnel. It should be plugged in there.)
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Team Owner
Joined: Jul 2006
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From: Kannapolis NC
I had the same issue with a 77 and ended up having to change the coax between the antenna and the radio. It is, as mentioned, a tiny, tiny wire in the center that carries the signal. You can troubleshoot by unplugging the antenna from the back of the radio and plugging in a temporary antenna. The ground plate should not cause what you're describing.
P.S. There is also a preamp in the radio that could be bad, hopefully not. Try the temporary external antenna to see.
P.S. There is also a preamp in the radio that could be bad, hopefully not. Try the temporary external antenna to see.
Last edited by 65GGvert; Sep 3, 2008 at 08:10 AM.
Thread Starter
Instructor
Joined: Jul 2003
Posts: 118
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From: Twin Lake Mi
I checked the reception tonight & I believe it has improved greatly but I think I'm going to try a temporary antenna & see if that helps more. When I was a kid, all the cars I had only had AM radios so I'm not real familiar with the reception quality on the stock radio for the 70. Is it normal for the FM to fade depending on the direction you are driving or if you are in a hilly area? I was about 25 miles from the station we were listeneing to & it was fading in & out. I deffinately have a better AM signal now. We listened to WOKY out of Milwaukee on the west side of mid Michigan. There is a fair amount of electrical noise with that though. I have all the shields in place on the wiring & such & have tried various filters without any luck.
Melting Slicks
Joined: Mar 2007
Posts: 2,100
Likes: 12
From: Frederick Maryland
There's a procedure referred to as "trimming the antenna". It's one few today ever remember about.
Turn your radio on and set it on AM and find a distant, but still audible station near 1400. Then pull the tuning **** straight off and pull off the outer ring...it's the "tone" adjuster I believe.
Behind it you should see a small screw over top of the tuning shaft. Use a small flat blade screwdriver and turn it back and forth until your reception comes in the clearest. You've just "trimmed" your antenna. Put the tone ring and tuning **** back on and you're good to go.
I'm not saying this is the basis of your problem, but it's a necessary adjustment for best reception on radios of that era.
It's not unusual for FM to fade in and out a bit for those radios. FM waves are line of sight. AM waves bounce.
Turn your radio on and set it on AM and find a distant, but still audible station near 1400. Then pull the tuning **** straight off and pull off the outer ring...it's the "tone" adjuster I believe.
Behind it you should see a small screw over top of the tuning shaft. Use a small flat blade screwdriver and turn it back and forth until your reception comes in the clearest. You've just "trimmed" your antenna. Put the tone ring and tuning **** back on and you're good to go.
I'm not saying this is the basis of your problem, but it's a necessary adjustment for best reception on radios of that era.
It's not unusual for FM to fade in and out a bit for those radios. FM waves are line of sight. AM waves bounce.
Team Owner
Joined: Jul 2006
Posts: 22,164
Likes: 4,172
From: Kannapolis NC
Trimming won't help FM. Try the temporary antenna. You can buy one for under $10 or borrow one. You can even stick a coat hanger in the antenna connection hole on the radio and if your reception improves, the cable or antenna are bad. You can trust me on this, give it a try.
Safety Car
Joined: Nov 2004
Posts: 4,359
Likes: 57
From: Mundelein Illinois
It sounds like a grounding problem, but if you get AM signal the antenna and coax cable are good. The one thread of wire that goes through the coax cable is good. If you have no AM then I would look at the coax cable or radio, but that doesn't seem to be your problem.
Thread Starter
Instructor
Joined: Jul 2003
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From: Twin Lake Mi
I picked up a cheap antenna last night & tried it. I don't think it was going in all the way to work. The pin is longer than the old one & I couldn't get the "snap in place" feeling I do with the old one. The triming did help for the AM. Looks like I'll have to give the coat hanger trick a try. I just want to be sure I've tried everything before I declare it to be as good as it's going to get. Is it a big job to run a new antenna? They aren't too expensive.
Melting Slicks
Joined: Mar 2007
Posts: 2,100
Likes: 12
From: Frederick Maryland
Universal antenna aren't expensive...the issue with them is that universal antennas are designed to ground to the body of a car when tightened down. That's assuming you have a metal car which a Vette isn't.
A correct Vette antenna will be more expensive for two reasons...the base is contoured to the body to fit like it should, plus it's made to ground in a different way. Under the rear deck is a piece of metal that acts as a ground plane and is also grounded to the chassis. Replace your antenna with a correct Corvette unit and everything will hook up properly.
You can also buy an inexpensive universal unit and work up a separate ground wire attached to the ground plane. Both can work equally well...one is easier and more expensive and one cheaper and requires more work.
There's also another alternative...Crutchfield sells a hidden antenna that works great. It runs about $40 I believe. It plugs into the radio normally and has a 12v power lead you connect to a switched source and then you can hide the unit (thin and a few inches long). It does work great and you can leave your original antenna in place and no one will know different.
A correct Vette antenna will be more expensive for two reasons...the base is contoured to the body to fit like it should, plus it's made to ground in a different way. Under the rear deck is a piece of metal that acts as a ground plane and is also grounded to the chassis. Replace your antenna with a correct Corvette unit and everything will hook up properly.
You can also buy an inexpensive universal unit and work up a separate ground wire attached to the ground plane. Both can work equally well...one is easier and more expensive and one cheaper and requires more work.
There's also another alternative...Crutchfield sells a hidden antenna that works great. It runs about $40 I believe. It plugs into the radio normally and has a 12v power lead you connect to a switched source and then you can hide the unit (thin and a few inches long). It does work great and you can leave your original antenna in place and no one will know different.
Thread Starter
Instructor
Joined: Jul 2003
Posts: 118
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From: Twin Lake Mi
Have you tried the Crutchfield antenna? I did try to put a ground to the metal grounding portion of the replacement antenna. It just feels like it is not going into position enough to make a good connection.
Instructor
Joined: Dec 2006
Posts: 213
Likes: 0
From: Loganville Ga.
There's a procedure referred to as "trimming the antenna". It's one few today ever remember about.
Turn your radio on and set it on AM and find a distant, but still audible station near 1400. Then pull the tuning **** straight off and pull off the outer ring...it's the "tone" adjuster I believe.
Behind it you should see a small screw over top of the tuning shaft. Use a small flat blade screwdriver and turn it back and forth until your reception comes in the clearest. You've just "trimmed" your antenna. Put the tone ring and tuning **** back on and you're good to go.
I'm not saying this is the basis of your problem, but it's a necessary adjustment for best reception on radios of that era.
It's not unusual for FM to fade in and out a bit for those radios. FM waves are line of sight. AM waves bounce.
Turn your radio on and set it on AM and find a distant, but still audible station near 1400. Then pull the tuning **** straight off and pull off the outer ring...it's the "tone" adjuster I believe.
Behind it you should see a small screw over top of the tuning shaft. Use a small flat blade screwdriver and turn it back and forth until your reception comes in the clearest. You've just "trimmed" your antenna. Put the tone ring and tuning **** back on and you're good to go.
I'm not saying this is the basis of your problem, but it's a necessary adjustment for best reception on radios of that era.
It's not unusual for FM to fade in and out a bit for those radios. FM waves are line of sight. AM waves bounce.