FM (broadcast) radio aerial.

[Carduelis]

I need to fit an aerial for a car radio I have on my Beneteau. I don't want the palaver of putting another one at the masthead and I already have a splitter to extract an AIS feed.

Has anyone successfully used one of the internal ones that are designed to be mounted inside car windscreens etc? I see that some of them have built in amplifiers which presumably makes up for a lack of signal strength.

 

[earlybird]

My Sony car radio in the boat works well on about 1.5m of ordinary insulated wire, run inside a locker. It could be longer, or extended with 75 ohm co-ax. using a car-radio aerial plug to connect to the radio.

 

[duncan99210]

I have a cute little fm dipole that looks like a T made out of tape with a coax plug on the leg. Stuck underneath the deck and into the car stero we've fitted. Gave a reasonable signal when we used it in UK before we left. Disconnected just now as Greek radio isn't worth listening to.

 

[Carduelis]

Wow, that sounds easy. I could just buy a length of coax and just strip off the braid for a metre or so. I'm guessing, from my limited knowledge of radio, that there would be an optimum length for this - some fraction of the wavelength perhaps.

Could any of the Engineers on here advise please?

 

[JohnGC]

I haven't done this for a few years but;

Take a length of coax.
Measure 1.5m back from the end.
At this point, carefully remove the outer insulation for about 1 inch.
Open up the braid without cutting it. You are aiming for a hole large enough to pull the inner core through.
Using a combination of bending and poking with a small screwdriver, ease the inner insulation and core back through the hole you created in the braid.
Pull the inner core completely out of the braid.
Pull the inner and outer sections in opposite directions.
You now have a 1/2 wave dipole on the end of a coax and no soldering was required.
Attach a suitable plug to the unaltered end and test.

 

[Langrick1]

Most FM broadcasts are around 100 Mc/s which is 3 metre wavelength so total length is about 1.5m or only strip 3/4 of a metre.

The aerial should be vertical - I think - most vhf broadcast with vertical polarisation. If its horizontally polarized the aerial should be horizontal.

Best of luck.

 

[JohnGC]

Most FM broadcasts are around 100 Mc/s which is 3 metre wavelength so total length is about 1.5m or only strip 3/4 of a metre.

The aerial should be vertical - I think - most vhf broadcast with vertical polarisation. If its horizontally polarized the aerial should be horizontal.

Best of luck.

Yes thanks; 1.5m total. Doh!

 

[Carduelis]

Very many thanks, this is just what I needed to know. There is a channel in the headlining/moulding which would be ideal for the above solution if horizontal is OK. If it needs to be vertical, finding a location will be a bit harder...

Just one other thought though. The shroud baseplate comes through the deck in about the right place. I suppose it wouldn't be possible to use a stainless shroud wire as an antenna?

 

[Langrick1]

Yes

Definitely try it horizontal - these things are a bit "select on test" anyway.

 

[Alpha22]

Optimal wavelength is largely irrelevant on reception aerials. Longer and higher wins the day. Go for a clip on the shroud.... simplest initial test solution. Broadcast FM is vertical.

 

[Billjratt]

Yes, don't go for horizontal or you will get fading at anchor etc.
I connect to the underside of a stanchion fixing bolt in the locker the radio sits in. That will work in 'civilization'
For poorer reception areas, a splitter on the Nargus active omni-TV aerial is the dBs...!