Does size matter? AM/FM Antenna options

[Sailon1]

The boat’s AM/FM 3’ antenna currently resides horizontally on a shelf in the cabin.

Will a longer antenna positioned outside improve reception? Is it worth the cost (minimal) and possibly poking a hole in the cabin to run the cable outside?

Your suggestions are, as always, appreciated.

[Jammer]

For AM a longer antenna will typically help. There are loop antenna designs that are usually best but they're bulky.


You may find that, for AM, a spreader or lifeline works as well as anything.



FM is like VHF and getting an antenna higher will help. Size does not ordinarily play a major role although there are certain shapes and critical dimensions that work best. There are FM antennas available commercially from Shakespeare and other maine antenna suppliers.

[S/V Illusion]

Just to be clear, not all FM is in the VHF/UHF spectrum; some are in the HF spectrum similar to broadcast AM station signals. Having said that, a longer, higher antenna will always out perform a small, low one.

[Bycrick]

Att he middle of the AM, 1000 kHz, the wavelength is about 300 meters, so a quarter-wave length is about 100’. Thus any antenna you’re likely to build is going to be electrically short and therefore "relatively inefficient." So almost anything will work, especially for receiving.

For FM, mid-band is about 3m, so a 1/4 wave dipole is only 2.5’ long. But it has no gain. Most FM stations are circularly polarized so the antenna orientation isn’t very important. The height of your antenna doesn’t make much difference either, regardless of the theory. If the transmitting antenna is on a hill at an effective height of 300’, moving your antenna up 50’ only adds a couple of miles to the theoretical horizon. Given the high-power of the transmitter, it won’t gain you much, if anything. Sure, some people use high-gain directional antennas on high towers to gain distance. But that really isn’t practical on a boat.

[denverd0n]

Originally Posted by S/V Illusion

Just to be clear, not all FM is in the VHF/UHF spectrum; some are in the HF spectrum similar to broadcast AM station signals.

Well, FM is a mode of transmission, so you can actually use that in any frequency range that you want, with the right equipment. On the other hand, commercial FM broadcast stations, at least in the United States, operate between 88 MHz and 108 MHz, which is well above the HF frequency range.

[hzcruiser]

It sounds as if you're just listening to commercial AM/FM radio? If so, poking holes might be overkill. If mainly listening at anchor, you can use a cheap rubber duck with some coax run through an open hatch.

[Lake-Effect]

Originally Posted by S/V Illusion

Just to be clear, not all FM is in the VHF/UHF spectrum; some are in the HF spectrum similar to broadcast AM station signals. Having said that, a longer, higher antenna will always out perform a small, low one.

Commercial broadcast FM is in the VHF band - approx 88 MHz and 108 MHz as previously stated, and commercial broadcast AM is roughly 0.53 MHz to 1.6 MHz, and is the MF band, not HF. Hairsplitting, I know.

To the OP - if it's an "auto" type radio with just one antenna input, the best results would probably be an "auto" style whip antenna mounted outside.

But don't be afraid to experiment with various lengths of wire stuck into the antenna jack, or waving around a whip antenna, just to see what makes reception better or worse. Walk around with it, poke it out a hatch on a stick, etc.

[pcmm]

Originally Posted by Sailon1

The boat’s AM/FM 3’ antenna currently resides horizontally on a shelf in the cabin.

Will a longer antenna positioned outside improve reception? Is it worth the cost (minimal) and possibly poking a hole in the cabin to run the cable outside?

Your suggestions are, as always, appreciated.

Before you get a new antenna, take the current one and mount it correctly. am/fm antennas are meant to be oriented vertically. That change alone should net a drastic improvement in reception.

[Spot]

Originally Posted by pcmm

Before you get a new antenna, take the current one and mount it correctly. am/fm antennas are meant to be oriented vertically. That change alone should net a drastic improvement in reception.

Originally Posted by Lake-Effect

Commercial broadcast FM is in the VHF band - approx 88 MHz and 108 MHz as previously stated, and commercial broadcast AM is roughly 0.53 MHz to 1.6 MHz, and is the MF band, not HF. Hairsplitting, I know.

To the OP - if it's an "auto" type radio with just one antenna input, the best results would probably be an "auto" style whip antenna mounted outside.

But don't be afraid to experiment with various lengths of wire stuck into the antenna jack, or waving around a whip antenna, just to see what makes reception better or worse. Walk around with it, poke it out a hatch on a stick, etc.

These type things would be my first step, outside the cabin vertical orientation, and probably with some sort of temporary mount like a piece of plywood with something non-slip on the bottom and a weight on top. If you can get more distant stations to come in then you are on the right track. Once the concept is proven, then look for mounts and a longer cable if needed.

[continuouswave]

Originally Posted by S/V Illusion

Just to be clear...

I don't think the comment really adds clarity.

Originally Posted by S/V Illusion

not all FM is in the VHF/UHF spectrum; some are in the HF spectrum similar to broadcast AM station signals.

Please give the frequency and callsign of any commercial broadcast stations in the HF spectrum that are authorized to use voice frequency modulation.

[Sailon1]

Thank you for that interesting response.

[S/V Illusion]

Originally Posted by continuouswave

Please give the frequency and callsign of any commercial broadcast stations in the HF spectrum that are authorized to use voice frequency modulation.

Too numerous to list. There are literally hundred of such broadcast stations using FM throughout the world in the HF portion of the spectrum. Think beyond the U.S.

[continuouswave]

Originally Posted by pcmm

Before you get a new antenna, take the current one and mount it correctly. am/fm antennas are meant to be oriented vertically.

The dominant polarization of commercial FM broadcasters in the USA is horizontal polarization. Many stations have added vertical polarization, but often at a reduced power level compared to their horizontally polarized signal.

AM Broadcast station are transmitting vertical polarization.

Generally any receiving antenna for AM Broadcast band is a miniscule length in terms of wavelength of the incoming radio signal. For example, at 800-kHz a wavelength is 1,230-feet. A three-foot antenna is thus 0.0024-wavelengths long. Many AM radios use an internal inductive antenna wound on a ferrite rod. The most effect antenna for AM Broadcast reception is a loop antenna.

For example:

https://www.amazon.com/Kaito-Tunable...dp/B001KC579Q/

ASIDE: a commercial broadcast station was required to monitor a local 50-kW AM station for messages regarding the Emergency Alert System (EAS). Their facility was built with excellent grounding and shielding, so reception of that AM signal inside the plant was very difficult. Installation of a small loop antenna on the EAS monitor receiver solved the problem.

My background: 45-years as an engineer in commercial broadcasting.

[continuouswave]

Originally Posted by S/V Illusion

Too numerous to list. There are literally hundred of such broadcast stations using FM throughout the world in the HF portion of the spectrum. Think beyond the U.S.

Okay, list one station.

[S/V Illusion]

Originally Posted by continuouswave

Okay, list one station.

And if/when I do, will you respectfully apologize for the implication I was incorrect?

Hint - Europe, Africa, S. and Central America, Asia, etc... in case you forgot.