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Antenna differences for AM/FM and 27 MHz?

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  • Antenna differences for AM/FM and 27 MHz?

    Currently have a 27 MHz radio and an AM/FM stereo receiver for music. The boat has two antenna bases - 27 MHz on the port side and AM/FM on the starboard.

    I have the two antenna's to suit but am unable to identify which is which as the labels have faded beyond readable. There are some slight differences:

    * the top antenna in the photographs is slightly taller than the other - by 30mm or so, they are around 180ish cm total length.

    * the internal wire on the top antenna in the photograph is wound around with even spacing while the bottom antenna's wire is wound much tighter as it gets to the tip.

    Are either of these indicators of being either the AM/FM or 27 MHz antenna?

    I tried the local boating shop to look at replacements but they didn't have the same brand/model to compare. These seem to be Kingray < https://www.kingray.net.au/kr-au > who now seem to be selling GME branded products only.



  • #2
    I have separate antennas for am/fm and VHF. The connectors are different and not interchangeable
    ....

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    • #3
      Are you sure one is for AM/FM? Those look, to me, like VHF and 27mhz.
      2008 Maxum 1800MX - 'Lottie-Da'
      1994 Proline 2510 - 'DrifteR ' <- project - ON THE WATER!
      1971 Concorde 27' - 'Little Angel ' <- sold

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      • #4
        The (lower) antenna with more wire in it is more likely the 27mhz one. It's likely approximating a top loaded vertical.

        A full size quarter wave antenna for 27 Mhz would be approximately 8.5ft or 2.6m if it was a straight radiator (or straight piece of wire) and it would be the most efficient.

        If you wanted to make it physically shorter, you would wind some of it on a non-conducting form (fiberglass, plastic etc) but it would still be electrically" 2.6m in length but would be shorter because some of the length would be in the form of an inductor (wire wound around a form)

        http://www.csgnetwork.com/antennagpcalc.html

        Cheers,

        Rick


        1987 FourWinns 211 Liberator, Originally an OMC 460 King Cobra.
        Re-powered in 2006 with a 1997 Mercruiser 7.4L Bravo III

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        • #5
          Originally posted by TBarCYa View Post
          Are you sure one is for AM/FM? Those look, to me, like VHF and 27mhz.
          The boat is 2001 built. These are the original antenna's and mounts fitted at factory in the original build. I don't believe that VHF was common on recreational boats here at that time.
          The boat is factory fitted with an AM/FM/CD Player and 27 MHz radio. The two antenna mounts correspond to these with the appropriate different connection types for each.


          Originally posted by dingbat
          I have separate antennas for am/fm and VHF. The connectors are different and not interchangeable
          The two antennas physically are interchangeable and both will fit on the others mount. The connectors on the leads from the mounts are different - one is AM/FM stereo receiver type and the other is the threaded ringed comms type.


          Originally posted by HT32BSX115 View Post
          The (lower) antenna with more wire in it is more likely the 27mhz one. It's likely approximating a top loaded vertical.
          Some great info there, thanks Rick! I'm certain that you are correct as at the boat ramp today I noticed another vessel with the same antenna setup, but only a single, went over and had a look and they had the same old 27 MHz GME radio and the antenna was the bottom one with the tight coils wound towards the tip.


          I've purchased a GME splitter today which splits the 27 MHz antenna to both 27 MHz and AM/FM - I was originally planning to discard the old 27 MHz unit but this way I can retain it for additional comms/backup. I then plan to remove the AM/FM antenna and replace with the GME VHF antenna which is the same style design and mount - this will keep the boat looking neat and original. I notice that the new VHF antenna is shorter than either of these two old ones...

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          • #6
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            take a picture of the connectors, the cb radio should have a pl259 connector, totally different from the fm antenna.

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