72 Correct antenna with AM/FM versus AM

[72 Super]

I would like to find the correct antenna for my 72. The truck originally had an AM radio, but someone has put an original AM/FM radio in it.

What antenna would came in a 72 with an AM radio? would it work with the AM/FM?

What is correct for an AM/FM?

Thanks,
Ray

[teeitup]

I am curious about this to Ray

[DANTIP]

I believe (and that's all it is), all radio antennas were collapsible mast until some time in early 72 when the fixed mast were used.

If anyone have definitive information, I'd love to see it.

Dan
Posted via Mobile Device

[Dave]

Not 100% sure, but I'll throw this out there anyway. Every truck that I've owned that had a factory am/fm in the truck and listed on the SPID, had a non adjustable mast.

[Sillyoldman]

None adjustable on all & same for AM & FM as far I know.

[special-K]

FM operates with a solid mast,so probably the solid masts were used. I never had a 67/72 that didn't have a fixed mast. All the newer antennae have been fixed,since most vehicles had FM

[haysonj]

FM requires a fixed length I believe it is 32 inches. A adjustable will work best if it is extended to 32 inches

[FirstOwner69]

Originally Posted by haysonj

FM requires a fixed length I believe it is 32 inches. A adjustable will work best if it is extended to 32 inches

I recall hearing this also back when AM/FM was new. The only thing that's a bit different is that I thought it was 31". So, somewhere around 31"-32" should give optinum reception. Just measure the length of a fixed mast and use that. I don't know what the original FM trucks came with. I've only seen adjustable masts on these trucks, but they all may have been AM radio equipped.

[special-K]

Yep,I meant to say "FM operates at a fixed length",when I said "...a solid mast". Same,but different. I always heard 31",but have measured some from different years and they vary slightly. I guess there's a little wiggle room,but telescoping masts are for AM or for those who want to lower for some reason,then readjust back to proper FM length. GM was smarter than most other companies and made parts that interchanged and used a mast that worked with either radio.

[72 Super]

This is really informing to me. I understand now that the length for the FM to work properly had to be 31-32 inches.

So did the adjustable antenna
only came on trucks with AM? Or was an year thing?

I had originally thought each radio would of came with it own antenna.

So I should be looking for a fixed mast antenna?

Thanks,
Ray
Posted via Mobile Device

[72 Super]

So it almost seems that all 72's came with the fixed mast antenna? Were adjustable ones for earlier years, AM or??
Thanks,
Ray

[hooverfish]

Does anyone have any additional comments or knowledge on the 'correct antenna' question,
discussed above, as it pertains to AM-FM radio reception ??

[truckster]

One of my Army qualifications was 25D - communications, which includes wave theory. So here's the scoop. If you take the frequency range of commercial FM broadcasts, a 31 to 32 inch antenna will give you 1/4 wave of the average range, which is the best overall compromise. If you had a favorite radio station at a specific frequency, you could easily calculate the perfect 1/2 wave antenna for optimal signal, but it would be over 5 feet long.

[Steeveedee]

The mast is 1/4 wavelength because the other half of the dipole is a reflected image in the ground plane (not a very good one, since the fender isn't all that flat). AM radios had an adjustable mast in order to pick up the lower end of the frequency if you were way out in the middle of nowhere, far from the station. FM is 88 to 108 MHz. Rule of thumb is at 1 GHz is wavelength 1 foot, so 100 MHz wavelength would be 10 feet (10 times lower frequency). Divide by 4 for the 1/4-wavelength yields 2.5 feet, which is 30 inches. 31- 32 inches is a compromise due to the lower frequency end of the FM spectrum. I designed and built aircraft and spacecraft antennas for about 10 years. There are antennas now that are much shorter than 1/4 wavelength, but that's fractal stuff like you would find inside a cell phone.

[kenn]

Hello I have a 72 with am/fm and an adjustable antenna I thought was original.

[Steeveedee]

It probably is. I don't know when the change over was started or completed. But if you have AM or AM/FM, you might need to adjust it. Almost nobody had an FM only radio in those days. I did see FM only cassette players, though.

[kenn]

Thanks, I always just extended it all the way but now I'll mark it, its too tall for the garage.

[Steeveedee]

Originally Posted by kenn

Thanks, I always just extended it all the way but now I'll mark it, its too tall for the garage.

Who listens to AM radio nowadays, anyway!? Just pulling your chain.

[Killer Bee]

1260 am k-surf

[Steeveedee]

Originally Posted by Killer Bee

1260 am k-surf

Well, there's a vote of ONE! JK, I'm sure that there's plenty of programming on AM radio. The last few years of commuting to work, the only time I listened to the radio was when traffic was jacked up. The rest of the time I spent listening to my iPod, which only has music I like and no dagbone commercials!.