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Old 30-07-2011, 14:52   #1
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FM Antenna Setup

Hello

We have an Am/Fm radio/CD player and are trying to get better FM reception via a FM antenna. To that extent, we have tried a few setups, such as an interior car antenna (works OK but not always) as well as a 6' cable antenna that only works sometimes. I also looked into "splitters" that use the VHF mast-top antenna but these create additional connections for the VHF cable, hence lesser overall output for the VHF itself. I've also seen the 3' or 4' fiberglass anttenae but think they are too large and difficult to find a suitable location on the boat.

Anyone with a better, more reliable (hopefully simple) FM antenna setup out there? Any help would be appreciated!

Thanks all
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Old 30-07-2011, 15:20   #2
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Re: FM Antenna Setup

I've used a Metz AM/FM s/s whip antenna for some years. It's mounted on my stern rail, and works very well. Guaranteed for life.

Metz Communication AM/FM Stereo Antenna

If you're in a poor reception area, you could mount it higher up, say on one of the spreaders.

Bill
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Old 30-07-2011, 15:29   #3
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Re: FM Antenna Setup

Thanks Bill, I know Metz makes quality products.....
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Old 31-07-2011, 00:23   #4
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Re: FM Antenna Setup

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Originally Posted by silverp40 View Post
trying to get better FM reception via a FM antenna...
Try a car antenna with a coil. These are about 60cm (2ft) long and can be mounted in a locker. It is also important that the earth/shield is connected to some metal in the water (via any route).

This could lead to galvanic corrosion, so it may be wise to connect it via a small Galvanic Isolator made out of four diodes and a small capacitor (see attached) no need for a high current GI as used on shore power circuits.

Any general purpose diodes are OK, such as 1N4001. For the capacitor, any general purpose ceramic around 100nF (0.1uF) or more will be fine. These can be bought for a few pence (cents) at Farnell, CPC, RS Components, Maplin, DigiKey, Tandy/Radio Shack...
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Old 31-07-2011, 00:53   #5
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Re: FM Antenna Setup

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This could lead to galvanic corrosion, so it may be wise to connect it via a small Galvanic Isolator made out of four diodes
Why the diodes? Why a DC ground? The capacitor makes a good RF ground. For that matter why an RF ground when VHF radios do just fine without?
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Old 31-07-2011, 05:12   #6
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Re: FM Antenna Setup

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Why the diodes? Why a DC ground? The capacitor makes a good RF ground. For that matter why an RF ground when VHF radios do just fine without?
It is true that the capacitor alone provides an RF ground, but a DC ground does no harm and helps with stability.

To be honest, I would have no problem just making sure that the antenna shield was directly grounded (perhaps through its own wiring, as with the VHF - the OP did not specify that the FM device was wired in), but on some of the technical groups I use there would have been a shout of GI!

However, all radio antennas need a ground plane; on a car it is the roof (boot, trunk etc), but on a boat it has to be the water. [Just read your profile, you know this already!]
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Old 31-07-2011, 10:20   #7
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Re: FM Antenna Setup

I seriously doubt any ground connection is necessary in this case.
It's a receiver, not a transmitter, and the FM band being 88 to 108 mhz only requires about 30" for antenna length.
The radio DC supply leads would act sufficiently as a ground plane.
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Old 31-07-2011, 23:12   #8
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Re: FM Antenna Setup

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The radio DC supply leads would act sufficiently as a ground plane.
But do we know the unit is connected to the power circuit? I think not, hence my suggestion.
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Old 01-08-2011, 02:57   #9
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Re: FM Antenna Setup

Put a VHF aerial in the back rail (if you don't already have one) The back rail will be a ground plane & the aerial forms a "spare" for the VHF radio as well.
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Old 01-08-2011, 03:06   #10
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Re: FM Antenna Setup

OT,

I recently noticed that my Icom VHF is not receiving Weather forecasts well at all. The ICOM VHF is much better... no problem. The fixed mount does work because I have tested it and hailed the launch service, but this is very close range. The fixed mount is on a splitter with the FM.

I do have a separate AIS on rail mounted antenna. Perhaps I should move the FM to the AIS antenna and leave the fixed mount without a splitter?

Aside from corroded connections or the antenna cable gone bad... why woulf those weather channels not come in?

Any thoughts?
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Old 02-08-2011, 05:34   #11
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Re: FM Antenna Setup

The AM/FM radio is connected in the normal manner to the DC power supply, hence the negative commons the boats'. I also always thought that the negative does not need to be grounded again...
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Old 02-08-2011, 05:36   #12
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Re: FM Antenna Setup

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Originally Posted by bill good View Post
Put a VHF aerial in the back rail (if you don't already have one) The back rail will be a ground plane & the aerial forms a "spare" for the VHF radio as well.
Bill, do you think a VHF antenna would work as a FM also??
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Old 02-08-2011, 05:51   #13
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Re: FM Antenna Setup

Yes And for stamps I use the top mast VHF aerial for Digital TV!!

Regards Bill Goodward
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Old 02-08-2011, 05:59   #14
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Re: FM Antenna Setup

Hi Bill

The VHF has a different connection that the FM radio at the end of the coax cable... Any suggestions as to how to make these ? I always thought a spare VHF antenna (not on the mast) would be a good idea!

Thanks much
Ovi
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Old 02-08-2011, 06:58   #15
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Re: FM Antenna Setup

The end on the VHF aerial will have a PL259. You get a barrel joiner which the same thread as the PL259. Then you make up a tail using a suitable length of coax with a PL259 one end & the female end to suit the car radio. This way you can still use it for emergency VHF aerial if needed.

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