My question is can an AM antenna be used on a FM radio? I have a 1947 ford and had the radio converted to an AM/FM radio. I am having a hard time finding an antenna that mounts on my cowl top properly. If I get an antenna from a restoration supplier, they may not know if the reproduction antenna is compatible or not. I read the difference in AM and FM antenna online but it was over my head. Thanks for the replies.
Original antenna will work fine as long as you can plug it into the new deck. I did that conversion on my 64 Chrysler - original AM, installed FM deck (with satellite radio) and the wire plugged right in. Basically for cars the antenna is just a stylish wire.
I used an old FM convertor to turn my OEM AM radio into AM/FM on my OT Ford (66). It used the original aerial without issue. Worked fine and without issue.
Strictly a marketing thing from what searches show. Back in the 60's when I started driving only a few and usually European cars had AM-FM radios. If the antenna on the car has the slide out pieces to extend it you can sometimes fine tune it for FM reception a bit. I remember sitting in front of the Tavern in Suquamish, WA and pulling the antenna on the 58 Merc colony Park wagon my folks had all the way out so I could pick up AM stations from Detroit or Chicago while waiting for my stepfather to come out of the tavern.
I think there's an optimum height for FM reception. 28-31" is in my head. Don't beat me up if I'm off tangent.
Yes, an old school antenna extended all the way out doesn't do FM reception much good. My cars all have a solid shaft antenna that has a fixed height. It might just be around 28 - 31 inches, I'm not sure.
I agree. When I was reading through this thread, I was thinking we used to adjust our antennas to 30”when we installed fm radios in our rides.
Antenna length is co-related to the wave length of a particular frequency. It is usually a fraction of the wave length. CB radio is on 27 meter long waves, the antennas were 1/4, half or 5/8 wave gain. The length of an antenna is much more critical in transmitting than for reception. Older radios had a terminal in the back of the set to attach an antenna. In rural areas it was sometimes attached to a barb-wire fence, allowing the listener to hear far away stations, particularly at night.
Optimal antenna length for FM is 33". Plus or minus a couple of inches won't make much difference in reception. Generally speaking the longer the better for an AM antenna. Frequency wave length vs antenna length is the determining factor in antenna gain. Radios use tuning internally to fool the radio into thinking is has a full wave length antenna feeding it. ELF, the military comms for subs is miles long vice the extra high frequency for satellite comms is only mm's long.
AM will work with almost anything. FM likes a 31" one-piece mast pointed straight up. not sideways under the dash.
The radio doesn't care, or at least that has been my experience. Just for chits and goggles, JC Whitney used to sell an "FM Filter" that went inline on the coax. The ad claimed that it improved FM reception.
A very effective FM antenna can be made with simple flat ribbon TV VHF cable, cut and soldered to a "T". With an AM antenna, a longer antenna will often just mean it picks up more noise and static a whole bunch better, and overloads the front end and loses selectivity between stations. Both AM and FM radios are coupled with tuned coils that are trimmed out to a certain length of antenna. It isn't the end of the world, but it won't work right if you stick something else on there.
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