replacement antenna
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Senior User
Joined: Aug 2003
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From: charlotte, nc
replacement antenna
This probably will sound like a dumb question, but when replacing the philco am radio for an aftermarket am/fm is a different antenna needed?
A friend of mine was telling he was getting horrible fm reception in the '68 firebird he just finished restoring. He tried a different stereo and a new antenna cable and finally someone asked him if the car originally had an am radio. Which was what it was. He installed an am/fm antenna and his fm radio came in fine. Anyone ever heard of this before?
A friend of mine was telling he was getting horrible fm reception in the '68 firebird he just finished restoring. He tried a different stereo and a new antenna cable and finally someone asked him if the car originally had an am radio. Which was what it was. He installed an am/fm antenna and his fm radio came in fine. Anyone ever heard of this before?
Post Fiend
Joined: Feb 2000
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From: Brea CA
replacement antenna
Nothing special about an FM car antenna. Just pull it out to 31 inches, this is a quarter wavelength of 100MHz center frequency of the FM band. The car body is the ground plane and makes up the other half of the quarter wavelength to give a half wavelength.
Barry
Barry
Post Fiend
Joined: Feb 2000
Posts: 5,130
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From: Brea CA
replacement antenna
Whoops that was fired from the hip. The FM band is 88 – 108 MHz which puts the center freq. at 95.54 MHz, where did I get 100MHz? Divide by the speed of light at roughly 300,000 kilometers per second gives 3.14 meters for a full wavelength. So ¼ wave of that wound be .785 meters or 30.9 inches, close enough.
Post Fiend
Joined: Jun 2003
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From: Black Hills of SD
replacement antenna
The 68 firebird may have had the one in the windshield and they didn't always work real well.
BB thanks for the wave length info, which sparked a thought. On several of the highboys I have owned I ended up either breaking the original antenna in the woods or just taking it off and installing one with a spring base over the stub. These were always longer than the original and seemed to get better reception on AM. It doesn't seem like those original ones were 31 inches long. A question though. If your antenna is longer than a quarter wave length is it detrimental?
BB thanks for the wave length info, which sparked a thought. On several of the highboys I have owned I ended up either breaking the original antenna in the woods or just taking it off and installing one with a spring base over the stub. These were always longer than the original and seemed to get better reception on AM. It doesn't seem like those original ones were 31 inches long. A question though. If your antenna is longer than a quarter wave length is it detrimental?
Post Fiend
Joined: Feb 2000
Posts: 5,130
Likes: 8
From: Brea CA
replacement antenna
Yeah the original antennas pull out a lot longer than 31" but they were for the stock AM radios. Longer is better, you can't pull it out long enough to hit a 1/4 wavelength for the lower AM frequencies.
Barry
Just remembered, on AM radios there is an antenna tuning screw near the jack where the coax plugs in. Turn on the radio, tune in a station around the middle of the AM band and turn the tuning screw in or out until you find the sweet spot. The signal strength will increase dramatically.
Barry
Just remembered, on AM radios there is an antenna tuning screw near the jack where the coax plugs in. Turn on the radio, tune in a station around the middle of the AM band and turn the tuning screw in or out until you find the sweet spot. The signal strength will increase dramatically.
Last edited by BB; Sep 7, 2003 at 02:23 PM.
Thread Starter
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Senior User
Joined: Aug 2003
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From: charlotte, nc
replacement antenna
The firebird was not a windshield antenna car, though the original antenna may have just been bad, who nows. I have heard that a missing or bad antenna will pickup fm but not am (or maybe its the other way around).
The truck I plan on buying has an am philco radio and a broken antenna. I will probably fix the antenna before switching radios, but want to pickup something that will work on am and fm. If I pickup up a used antenna at a junkyard, I can get anything that fits (and works). BB, that is what you are saying?
The truck I plan on buying has an am philco radio and a broken antenna. I will probably fix the antenna before switching radios, but want to pickup something that will work on am and fm. If I pickup up a used antenna at a junkyard, I can get anything that fits (and works). BB, that is what you are saying?
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Post Fiend
Joined: Feb 2000
Posts: 5,130
Likes: 8
From: Brea CA
replacement antenna
Yes you could use any antenna that fits. Can you find a good used antenna in a junkyard? They sell new replacement oem style antennas.
Barry
Barry
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