AM radio reception poor

[71CHEVYSHORTBED402]

Recently bought a truck with a beautiful AM radio. The reception is very poor, though it does improve somewhat when I jiggle the antenna. I haven't taken the antenna apart yet, but thought to ask what's most likely to cause poor reception? Also, what's the cylinder component called that fits behind the radio? Name escapes me..Perhaps that component may be the problem. Thank you.

[FirstOwner69]

My original AM was poor from day 1. I got another from the junkyard in the 70s. It was just as bad. Replaced the antenna with another from GM. Still no good. I now have a van AM/FM disguised to look like a truck AM/FM. It works great.

Things to do to try to improve...
- Since you say it improves when you wiggle the antenna, make sure it is grounded effectively by removing any paint or rust on the underside of the cowl where the bottom mount block contacts.
- There is a fine tuning screw labeled with something like "adj ant" above the shaft behind the tuning knob on the right. You need to tune the radio to a given frequency station (I THINK it's somewhere between 1200 and 1400, but not sure). Once you find a station, use a small screwdriver to rotate the screw. It MAY improve.

Jim

[71CHEVYSHORTBED402]

I never noticed that screw before. I'll give both ideas a go, thank you Jim.

[FirstOwner69]

Originally Posted by 71CHEVYSHORTBED402

I never noticed that screw before. I'll give both ideas a go, thank you Jim.

Also (and I know you know this!), if the antenna is original, the cable is attached at the base and is removed by pulling it off. Be sure it is tight and free of corrosion. Same with the connection at the radio.

[71CHEVYSHORTBED402]

Originally Posted by FirstOwner69

Also (and I know you know this!), if the antenna is original, the cable is attached at the base and is removed by pulling it off. Be sure it is tight and free of corrosion. Same with the connection at the radio.

Exactly....You see my "new" truck. I like it a lot, less the rust anyway.

[68c10airstream]

Moving the antenna around with some improvement would indicate a poor ground. If the antenna lead was removed from the back of the radio and the lead was in your hand, a voltmeter would be used to check continuity between the pointed end and the antenna mast, basically no resistance. The outer silver end of the lead is grounded to the body where the antenna mounts to the cowl panel. I suspect this is poor.

Take the voltmeter and touch the silver outer sleeve end of the pigtail to one meter lead and touch the other meter lead to the door striker area (no rust and usually shiny from use) and you should see basically no resistance if perfect.

Remember that the cowl panel underside is probably bare steel and been scratched by the antenna base through all the years, so you could unthread the antenna mast and base, move it off to the side and try to sans the underside of the panel and reinstall and check.

Another way of looking at this is the radio needs to have the antenna circuit brought out of the radio box and extended, the circuit needs to be complete to the mast, grounding the radio box to the antenna mounting base to help prevent interference from outside sources, and not have the circuit leak to ground getting to the mast.

The last electrical check with the pigtail lead in your hand again would be to touch one meter lead to the pointed end and the other lead to the silver sleeve (at the pigtail end) and there should not be any continuity showing. Again, if there was continuity the radio circuit would be leaking to ground.

Enough of my long winded diagnostics, good luck!

[71CHEVYSHORTBED402]

Thank you. I need to get a volt. meter.....Once I do I'll wonder why it took so long.