A little OT for this group, but I figure you guys are the experts!

I've got a boat, it has an VHF FM Car Radio with a car aerial. The first
problem is that there is no ground plane, the boat is GRP. It is also lying
horizontally, it is too long to be vertical.

I want to replace the aerial something a bit more suitable. Modern cars seem
to have much shorter aerials, so is there a coil involved?

Any suggestions on making or buying a replacement?

BTW, the radio has a DIN antenna socket, so 150 Ohms I think?

--
Nigel M
G1NDM (a long time ago)

Nigel Molesworth wrote:
A little OT for this group, but I figure you guys are the experts!

I've got a boat, it has an VHF FM Car Radio with a car aerial. The first
problem is that there is no ground plane, the boat is GRP. It is also lying
horizontally, it is too long to be vertical.

I want to replace the aerial something a bit more suitable. Modern cars seem
to have much shorter aerials, so is there a coil involved?

Any suggestions on making or buying a replacement?

BTW, the radio has a DIN antenna socket, so 150 Ohms I think?

Modern cars use active antennas.

Nigel Molesworth wrote:
A little OT for this group, but I figure you guys are the experts!

I've got a boat, it has an VHF FM Car Radio with a car aerial. The first
problem is that there is no ground plane, the boat is GRP. It is also lying
horizontally, it is too long to be vertical.

I want to replace the aerial something a bit more suitable. Modern cars seem
to have much shorter aerials, so is there a coil involved?

Any suggestions on making or buying a replacement?

BTW, the radio has a DIN antenna socket, so 150 Ohms I think?


IME,Most car radios are sensitive and selective enough to pull in local
stations with only a short wire hanging out of the antenna socket. I've
routinely checked them out on the bench,and just stuffed a piece of
hookup wire in the antenna jack,works fine.
Maybe you could just run a wire up some vertical-surface of the boat?

There *IS* a ground plane-The water. When the boat is in the water,the
water itself is the ground plane.

On Sun, 28 Dec 2008 12:10:57 -0800, PhattyMo wrote:

Maybe you could just run a wire up some vertical-surface of the boat?

What about 1/4 wavelengths, and all that stuff?

Nigel Molesworth wrote in
:

On Sun, 28 Dec 2008 12:10:57 -0800, PhattyMo wrote:

Maybe you could just run a wire up some vertical-surface of the boat?

What about 1/4 wavelengths, and all that stuff?

Powerboat or sail? I recommend a quarter wave for sail, but 5/8 should
work on most powerboats. If you can mount atop a metal mast 1/4 wave
should easily do the job. I get really good broadcast FM reception on my
FT897D from my dual band mobile antenna out on the back deck. For receive-
only with good broadcast signals, impedance matching is not that much of a
concern. If you're trying to DX, that's another story, involving yagis.




--
Dave Oldridge+
ICQ 454777283

Nigel,
How long is this antenna?
- 'Doc

Nigel M, former G1NDM wrote:
"Any suggestions on making or buying a replacement?"

I`ve installed coaxial antennas at VHF which worked well on boats. They
consist of a quarter-wave rod insulated and mounted on a quarter-wave
cylindrical skirt which surrounds the coax feedline. The match is good.
There are no radials to poke eyes. The assembly makes a half-wave
vertical antenna.

At 100 MHz, the wavelength is about 3 meters so the overall length of an
FM broafcast antenna should be about 1.5 meters. You likely can find
such an antenna for sale ready made. If not, it is not difficult to make
your own. The folded dipole made from TV twinlead also works well but
presents a 300-ohm impedance and may not work as well with your DIN
connector. It also requires suspension. The coaxial antenna usually is
equipped with a small mounting pipe surrounding the coax.

Best regards, Richard Harrison, KB5WZI

On Mon, 29 Dec 2008 08:29:15 -0600, (Richard
Harrison) wrote:

At 100 MHz, the wavelength is about 3 meters so the overall length of an
FM broafcast antenna should be about 1.5 meters.

I've got about half of this, maximum. What can I do?

Nigel M. wrote:
"What can I do?"

You are installing an FM receiving antewnna inside. Go for a twinlead
dipole about 5 feet long and accept the received signals you get. Range
is line of sight so the nearby stations with high antennas will probably
be received satisfactorily. MFJ may sell such a dipole readymade.

Best regards, Richard Harrison, KB5WZI

On Wed, 31 Dec 2008 10:25:15 -0600, (Richard
Harrison) wrote:

Go for a twinlead dipole about 5 feet long

Like I said in the post you replied to, I have about half this.