C-4 poor radio reception

[Jim W.]

New to the Technical Dicussion process. I have a customer who had brought his 85 corvette in a number of times over the past 4-5 years and has continuely had poor reception with his corvette am/fm radio. We found the cable pulled apart at the antenna and replaced the cable. The radio worked fine. later the antenna motor drive went aout and we replaced the complete antenna. Now here a year later the customer drives the car for the first time in 10-12 months and complains that the radio has poor reception. Any ideas on this? Is there anyone who has a receiver amplifier for these radio reception woes?
Jim

[Jim T.]

Re: C-4 poor radio reception

There is radio antenna maint mentioned in the 1985 Corvettes service manual. Not knowing what the antenna is exposed to you could try raising the antenna and leaving it up, clean the antenna and apply light oil.

The 85's radio is a lot easier to remove than an early model C3.

[Jim W.]

Re: C-4 poor radio reception

Thank you. I'll try that!

[Jack H.]

Re: C-4 poor radio reception

A bit more diagnosis might be an assist...

On dual band radios (AM/FM), the radio's sensitivity to antenna continuity is MUCH greater under AM band operation than with FM signal reception. In a major metro area, a faulty lead-in cable from the antenna will render AM reception almost non-existent (all but the STRONGEST stations) while FM reception can continue to work reasonably well.

So, assessing the reception difference between AM and FM band use can help fault isolate an antenna continuity problem QUICKLY! One of the first things the mechanics at our shop did when an owner complained of poor radio reception, was to evaluate AM vs. FM signal reception.

If AM was spotty but FM was reasonably good, the mechanic would then unplug the car's built-in antenna and connect an el cheapo, WalMart, antenna with captive lead-in cable.

If that made a DAY & NIGHT difference in the radio's signal reception, the diagnosis was done--car has an antenna interconnect problem. Plus, a WalMart, el cheapo antenna is a whooping $10 item. That's about as cheap as a shop tool gets these days!

[Jim W.]

Re: C-4 poor radio reception

Thank you very much. We are not sure why we had great AM reception when the cable was replaced (New) and then Later the entire antenna when the problem re-occured. We will definetly try this isolation test that you explained and see what results we get. We keep a couple of different types of "Cheap Antennas" handy especially for bench testing purposes. Thanks again.

Jim

[Jack H.]

Re: C-4 poor radio reception

If there was an antenna interconnect continuity issue, that would certainly explain a MAJOR improvement in AM band reception... One reason I walked through the issue was the AM/FM difference can be a helpful over the phone diagnostic.

Also, I have seen Jeckyl & Hyde problems that came from this aspect. The single conductor inside the antenna lead-in cable is typically human hair thin. If it fatigue fractures, either at a solder joint on the end of the cable or somewhere in between), it's possible to get intermittent contact.

Sometimes the broken cable touches at the fracture site and you get reasonably good continuity/signal reception and other times the broken ends split apart. These can be 'fun' to diagnose!

On the earlier cars, the cable integrity problem can result from interior restoration. The carpet is ripped up and discarded with fresh reproduction carpet (and jute) laid down. The lead-in cable can suffer damage in the process from simple touch & side loading stress...

[Jim W.]

Re: C-4 poor radio reception

Jack. Thank you very much. When we get the car in our shop again next week we will look at all of these scenarios. It is actually cheaper for us to buy and install everything new rather than spending so much time doing diagnostics.

Jim