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AM/FM - VHF Dual Purpose Antenna

Old 10-13-2015, 05:39 AM
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Default AM/FM - VHF Dual Purpose Antenna

Are there any concerns with a combined VHF - AM/FM antenna, specifically with the range or clarity of the VHF? Is there any chance that the AM/FM signal interferes with the VHF when in such close proximity sharing the same antenna? I've heard people recommend against using a shared VHF antenna, not sure if that's just old school thinking or if there's merit to it.
Old 10-13-2015, 09:32 AM
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Originally Posted by Auburn1 View Post
Are there any concerns with a combined VHF - AM/FM antenna, specifically with the range or clarity of the VHF? Is there any chance that the AM/FM signal interferes with the VHF when in such close proximity sharing the same antenna? I've heard people recommend against using a shared VHF antenna, not sure if that's just old school thinking or if there's merit to it.
I had one on a boat of mine years ago. Didn't work well at all for either so I ditched it shortly after. Don't know if they've made any improvements over the years, but as for me, I wouldn't buy it again.
Old 10-13-2015, 11:40 AM
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AM/FM radios need minimal antennas to work well...see if you can even find the one in your car, for example.

I would not combine entertainment stuff with emergency gear...a simple wire is usually fine for AM/FM reception.
Old 10-14-2015, 02:11 PM
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Depending on where you boat will determine what FM/AM antenna you need. I boat offshore lots so I installed a Shakespeare Marine AM/FM antenna and installed on top of the T-Top. Works great. If close to radio stations as Karl mentions a piece of wire will work. Just depends on how far you travel from the transmitting towers themselves or trying to pick up that one station you prefer to listen to. I would always advise not to use the same antenna for VHF and AM/FM.
Old 10-14-2015, 04:13 PM
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AM/FM radio antennas in cars are kind of a mystery to me...most cars in the past 20 years have the antennas embedded in the laminated windshield and are horizontally-polarized and look like simple dipoles.

When car antennas were mounted on fenders, they were obviously vertically-polarized. Not sure, but I think all AM/FM towers use vertical polarization...cross-polarization generally results in ~3dB attenuation, so if just running a wire inside the console, I would start by orienting it vertically.

But, then again, many stereo home receivers came with a twin-lead horizontal antenna, basically a folded-dipole and they, too, worked fine.
Old 10-15-2015, 04:37 AM
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I believe most FM stations use circulator polarization or dual polarization. I leave my marine FM/AM antenna horizontal 99% of the time with no issues. Jim
Old 10-15-2015, 06:27 AM
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I installed the simrad antenna splitter (NSPL-400) this year to allow me to use one of my existing VHF antenna's for their AIS transponder.

Allows two VHF devices and one FM output. No detectable loss in signal strength or quality to the VHF radio. I have two radios and I use Ch 27 radio check on both so I can compare them fairly well against each other.
Old 10-15-2015, 06:35 AM
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Yes this can work, but I have had issues with them as well. When it comes to my VHF radio, I will not compromise my safety with a filter to allow FM/AM reception. Jim

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