FM radio antenna earthing

KAL

KAL

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We have an ordinary Sony RDS car stereo on board, which has lost the ability to pick up stations. I bought a replacement aerial and tried it yesterday, but it made no difference. Whenever I've fitted one to a car, it has always needed a good earthing to the car body, but I wondered if anyone could advise how they have managed this on their boat.

Is there a type of audio FM aerial that is designed for use on a boat, perhaps getting its earth from the radio itself?

Any help gratefully received. :D
 
Antenna inner is connected to chainplate. Suspect Paulrainbow might be right, but at least it still works taking an aux input from iPad to play other music. I do miss the radio though...
 
Try plugging in a length of coax with a couple of feet stripped, with the braid and core led in opposite directions.
 
FM domestic radio antenna requirements are no different to VHF com on a boat except that the frequency is lower so needs longer antenna about 30 inches for each 1/4 wavelength and polarisation may be horizontal or vertical.
However being receive only with high powered transmitters people are often satisfied with all sorts of antennae.
Hence ideas of coax centre to toe rail would technically be a terrible antenna but radio may sound fine.
The best antenna then might be a coax cable from the radio up as high as possible with 2 wires of about 30 inches long one to the centre and one to the outer. These should be stretched in a line and try either horizontal or vertical fro best fringe performance. However it does sound like the OP radio is not working. If it gives a good strong hiss sound then speakers etc are OK. May just be tuning problem which can be complicated with digital selection radios. olewill
 
KAL said:
I might try a splitter like this:

http://www.force4.co.uk/department/...-aerials-vhf-am-fm-splitter.html#.V0zCAJB4WrU

...because if the radio is not faulty, it might solve my problem, but if it is, I'm going to need one of these anyway to provide a decent signal to whatever I replace it with.
Click to expand...

Better yet, why not fit a cheap VHF antenna to the pushpit. Site the cable, with a PL259 connector, near your VHF and make a cable up to go from there to the FM set. If your VHF antenna fails you just disconnect the FM antenna and connect the PL259 to the VHF.
 
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nigelmercier said:
Those should be made illegal in some way.
Click to expand...

A 'splitter' which uses the fact that two signals are at different frequencies is a sound concept.
But you need a lot of isolation from VHF tx to FM Rx, depending on what the stereo is spec'd for.
The stereo is not likely to be designed to have even a small fraction of 25Watts stuffed up it!
Such a passive splitter aka 'diplexer' could be a good solution for sharing an antenna between AIS receive only and an FM stereo.
If it's of good quality and sufficiently water resistant etc etc.
I know a few companies that will make you a nice one for a few £k..... !
 
Going back to the OP.... If we may???

As I understand it the shield/braid of the radio antenna socket will be electrically connected to the radio's chassis and therefore to the -VE terminal???

This should therefore also be bonded to the boat "earth" and then to the sea.

If not, on my SH radio there is an "earth" stud on the rear that it is recommended is bonded to the sea...... To obtain maximum transmission and reception the vertical stick in the air must be counteracted with something to create the dipole that is part of the whole antenna setup...... The sea makes a near perfect ground plane, essential for good propagation, but only if it is connected!!!!
 
Alpha22 said:
Going back to the OP.... If we may???

As I understand it the shield/braid of the radio antenna socket will be electrically connected to the radio's chassis and therefore to the -VE terminal???

This should therefore also be bonded to the boat "earth" and then to the sea.

If not, on my SH radio there is an "earth" stud on the rear that it is recommended is bonded to the sea...... To obtain maximum transmission and reception the vertical stick in the air must be counteracted with something to create the dipole that is part of the whole antenna setup...... The sea makes a near perfect ground plane, essential for good propagation, but only if it is connected!!!!
Click to expand...

At VHF, anything other than the coax outer is not a direct connection, it will look like an inductor.
The body of the radio and the sheath of the coax do pretty much all the 'counterpoise'.

The antenna should not need to be very good to pick up a strong local FM signal. Any old bit of wire will probably work just as well as the average portable radio.
You should only need to go to much effort if you want to get FM several miles offshore or up wooded rivers etc.

Just a thought, check the stereo does not have a LO/DX setting, set to LO i.e. local it will attenuate the signal.
Also check the RDS is not set to any strange mode....
The other earthing may matter to the audio side though!
 
PaulRainbow said:
I'm with Nigel. Plus, why spend 30 quid on a splitter when you can have a backup VHF antenna for nearly the same money.
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Agreed, what a terrible bit of "technology"! Inevitable attenuation on both transmit and receive plus the slightest whiff of RF on transmit is going to do the front end of any connected domestic receiver no end of harm. It gives well designed, proper, active splitters a bad name. Avoid !
 
nigelmercier said:
For which task I'm sure it performs adequately. But what it does to a VHF transmission makes me shudder.
Click to expand...

Having taken apart one from what most people would assume to be a reasonably reputable manufacturer and seen the quality of soldering and how it was constructed I removed it from my boat as it would be easy to see how it could fail and compromise the integrity of the VHF circuit.

Stereo now has its own aerial!
 
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