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Optimum antenna length for FM radio?

Discussion in 'Ham Radio - CB - Trail Communications' started by RangerX, July 11, 2001.

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  1. RangerX

    RangerX Elite Ranger Staff Member Moderator Elite Explorer

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    Is there one? I seem to recall hearing once that 40something inches would give the best reception.
     
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  3. Sandy

    Sandy Well-Known Member

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    Antenna length is based on frequency not FM or AM modulation.

    What frequency are you working ?

    73,
     
  4. RangerX

    RangerX Elite Ranger Staff Member Moderator Elite Explorer

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    Sandy, I have no clue how to answer your question.
    On the off chance you think I'm a 'knowledgable radio guy' asking about some other type of radio, I'm talking about my stock Ford am/fm radio/cassette and stock antenna. I was hoping you or Ray might know.
     
  5. Sandy

    Sandy Well-Known Member

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    RangerX,
    No problem here, I thought you were setting up a two way radio in your vehicle, i.e. CB, HAM...

    The stock radio antenna that comes with the vehicle is a good compromise for all of the station that your radiocan receive or for any AM/FM broadcast radio that you may buy.

    The only time you should worry about the length of an antenna would be if you wanted to listen to one station in particular; you would then find out the broadcast frequency and have an antenna cut to length for that specific frequency. BUT, I have never heard of anyone having a custom antenna made for the AM/FM broadcasting frequencies.

    If you do not receive the stations that you want or the station does not come in as well as you would like it, it may be the radio itself. Look into an after market radio; one with a better receiver than a stock radio. Buy a name brand, i.e. Pioneer, Sony, or any other big company.

    I hope all of this helps, I tend to go on and on.

    73,
     
  6. RangerX

    RangerX Elite Ranger Staff Member Moderator Elite Explorer

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    Sandy, nothing wrong with going on and on, there's no such thing as too much information!
    I'm not having a problem with reception. I was thinking there's probably one length on a stock adjustable antenna (it telescopes) that would work best for the whole FM band, but your comments lead me to think that isn't true. I realize it's pretty trivial, but is fully extended the position it's meant to be in? I'm thinking free optimization, here!
     
  7. Ray Hutchinson

    Ray Hutchinson Moderator Emeritus

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    Braodcast FM antenna length

    Bill,

    You can calculate the length of any 1/4 wave antenna by dividing 234 by the frequency desired in mHz. This gives you the approx. length in feet. To get it in inches, simply multiply by 12.

    So for FM broadcast, which has a range of 88-108 mHz, you could calculate for mid band (unless you have a special station you listen to all the time). This would be 98 mHz. so....

    234/98 = 2.388 ft X 12" = 28.7"

    If you go to the bottom of the band, 88 mHz it becomes 234/88 = 2.66' X 12" = 31.9"

    Just for the fun of it, I measured the factory antennas on three cars and they ranged from 29" to 32", essentially what we calculated above. I'd probably go for the 32" length, since recieve antennas aren't as length critical as transmit antennas. Hope this helps.
     
  8. Sandy

    Sandy Well-Known Member

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    Telescoping Ant

    Ok on the antenna telescoping... that is a little different, have never heard of it on an FM mobile antenna.

    Try Ray's method, as was mentioned, it will work.

    73,
     

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