AM FM ANTENNA QUESTION

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CFD244

CFD244

"I LOST MY ID IN A FLOOD"
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Hi Folks

Can anyone advise if an AM/FM radio from a 73 Swinger will work with an antenna that came from an AM only car? Not sure if they used the same antenna? I can't get any sound from an AM/FM unit on the bench. I hear it click on, but nothing from the speaker.

Thanks
 
I put a factory AM/FM in my 70 Swinger with the original AM antenna and it works good.
 
IIRC, on the bench - the base of the antenna needs a ground jumper to the neg side of your power supply. And a good signal, of course. Ohm out the antenna also, I have seen more than one go bad at the center conductor.
 
Demonic said:
IIRC, on the bench - the base of the antenna needs a ground jumper to the neg side of your power supply. And a good signal, of course. Ohm out the antenna also, I have seen more than one go bad at the center conductor.
Click to expand...

That is not really true. The antenna mount is supposed to be grounded to the car body, which is not exactly the same thing.
 
I think there is continuity between the metal ferule on the cable that plugs into the radio (not the center stud). and the antenna base. By grounding the radio chassis, I think you have effectively grounded the antenna base, or am I off base......So to speak (lol).
 
I have plugged old car antennas to radios on athe workbench doing a bench test. Never grounded anything. The antenna wire coax has an inner wire thats the + to the Male center pin, and braded shielding that's the negative on the outer part of the plug. I do not believe antennas are made as AM or AM/FM specific.
 
So.......I have two am/fm's. Tried them both. Bat pos to red wire, bat neg to mounting bolt stud, black wire to 8 ohm speaker neg, green wire to 8 ohm speaker pos. Antenna connected.

One radio powers up, but no output on either am or fm. Not even static. Other radio powers up, can hear faint radio signal on fm but nothing on am. Both radios motorola........

I tried an old am connected the same way and got varying tones of hums at a loudness consistent with listening levels. This radio is a Bendix.

Any suggestions before I head off to the radio repair shop?.......Or am I missing something in my connection layout?
 
The one you can hear..........try using a long length of wire plugged into the center hole of the connector---maybe your antenna assembly is shorted. You can check that with an ohmeter. With the antenna laid out IE on wood bench, check continuity across the pin and shell of the connector. It should be open.

For AM radios (used to) have an antenna trimmer. This is usually an obvious, recessed screw somewhere near the antenna connector, usually facing down, so you can adjust it with the radio bolted in place. Usually, you tune in a weak station (or just noise) up around 1400-1600 khz and peak the screw back and forth for maximum noise.

For the one you cannot hear, is it possible it is stereo? Only two speaker wires? Try both wires, one at a time to the speaker, and then try the other speaker wire to ground

Last, what is the possibility the speaker is bad?
 
67Dart273 said:
For AM radios (used to) have an antenna trimmer.
Click to expand...
In 67 it is behind the tuner knob. Not sure about other years

moparmat2000 said:
I do not believe antennas are made as AM or AM/FM specific
Click to expand...
more or less correct. AM is a longer wavelength and needs to be longer antenna, FM is around 31 inches IIRC

But... Both radios, am or am/fm should work fine
 
The antennae originally had a couple clips on the base with teeth that helped it to ground to the body. I dont think its necessary for it to work but probably helps reception.
 
A single wire in the antenna hole (inner one) will work as an antenna for testing
 
Pretty strange.......With the AM only radio that I have, I was getting loud static (Bendix). With both AM/FM Motorola radios, I was getting nothing (vague music FM signal on one). Almost seems like the power output doesn't work. Normally, I would just take it in, but for both radios to be NFG......I thought I was missing something.
 
Dana67Dart said:
In 67 it is behind the tuner knob. Not sure about other years

more or less correct. AM is a longer wavelength and needs to be longer antenna, FM is around 31 inches IIRC

But... Both radios, am or am/fm should work fine
Click to expand...

Yeah but neither is optimized. FM goes all the way from 88-108mhz so this encompasses a large change in antenna length. AM is incredibly low in frequency by comparison, but it is nearly a 3:1 frequency multiplication-------about 500khz to about 1500 khz. A quarter wave whip on 1500khz, more or less, would be about 160 feet!!! (This is more or less depending on radiator construction). A 500khz whip would be 3X that height!!!!

By the same reasoning, an 88 -108 mhz FM whip would be around 33-27 inches
 
I also read somewhere that the optimum length of an FM antenna is 31 inches. All my cars from '69 thru '74 had this length. I also used one of these with an old,, generic AM/FM in my shop. I extended the cable and placed (antenna) in corner area - out of the way. Worked well, so, make sure your own radio works as it should - prior to installing in dash.
 
I bought an AM (237 I think) looks good, clean in the inside, I could raise and lower the volume, the speaker would increase or decrease in crackle volume but no stations would tune in.

I bought a repair book but I need a signal generator and oscilloscope to do any troubleshooting
 
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Thanks for everyone's input. I tried everything with no avail. I guess it's off to the shop!
 
Have the shop detail what exactly they did on each radio. Might help others.
 
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