FM radio aerial?

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prv

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Anyone have any advice for getting good (broadcast) radio reception on board? KS's current audio arrangements are distinctly ad-hoc, and I have been charged with making them better before she goes back in the water in a few months' time. The radio part of the arrangement is a small "walkman" style unit which I assume uses its headphone cable as an aerial. However, despite running this cable up to the deckhead and down again on its way to the cheapo eBay amplifier that runs the speakers, reception is pretty poor.

Would it be completely daft to connect to the chainplate bolt that's behind the radio location, and hence to the rig?

I vaguely remember such a thing as an FM splitter that uses the VHF aerial - worthwhile, or best avoided?

Any other ideas?

Cheers,

Pete
 
prv said:
Anyone have any advice for getting good (broadcast) radio reception on board? KS's current audio arrangements are distinctly ad-hoc, and I have been charged with making them better before she goes back in the water in a few months' time. The radio part of the arrangement is a small "walkman" style unit which I assume uses its headphone cable as an aerial. However, despite running this cable up to the deckhead and down again on its way to the cheapo eBay amplifier that runs the speakers, reception is pretty poor.

Would it be completely daft to connect to the chainplate bolt that's behind the radio location, and hence to the rig?

I vaguely remember such a thing as an FM splitter that uses the VHF aerial - worthwhile, or best avoided?

Any other ideas?

Cheers,

Pete
Click to expand...

Why bother with FM, its going to be DAB surely!
 
When we installed the FM radio on Little Dove it was a car type unit in one of the saloon lockers. It happened to be right next to the chain plates. We connected it very carefully to the chainplates and thus to the rigging.

I then tested it without the connection and a car type aerial in the locker. No difference as far as I could hear.

Might be different way offshore.
 
Pete, a thought here - if your 'walkman style' thingy doesnt have an external aerial socket how are you proposing to connect to any aerial other than that built in ?

btw, FM and DAB signals are close enough in wavelength that if it works for FM it should work for DAB. Especially if the FM aerial was a pukka half wave dipole.
 
I installed an aerial splitter to use the masthead VHF aerial - didn't seem much better than laying an car VHF aerial in a locker up against the bottom of the deck.

Would using a chain plate & the rigging make the radio more susceptible to damage from lightening?
 
FM broadcast radio

An ideal FM antenna is a vertical rod about 24 inches long with a decent ground plane ie earthed base of a size larger than 24 inches across. This feeds a 50 ohm coax cable to the radio.
Alternatively a 1/2 wave antenna consists of 2X 24 inch rods one to the centre and one to the braid of the coax cable. These should be vertical not horizontal as in TV.
Now the problem is that most radios are made for AM MW/LW and at these frequencies the antenna and especially the cable requirements are completely different. MW requires a very low capacitance shielded (coax) cable. So you end up with car radios using a compromise which really means that for best results (range) you should use an antenna cable as specified for the radio. (including length)

I would suggest that a car radio is generally must more sensitive than portable or walkman style and of course are designed to use an external antenna. Of course antenna will work best when as high as possible.
So I don't know if any of this is any help. For limited range performance almost anything will work. And of course the range of VHF FM is quite delineated. ie when you get to the extreme of range anything conks out quickly and even the best antenna will only help a little to improve range. good luck olewill
 
RobbieW said:
Pete, a thought here - if your 'walkman style' thingy doesnt have an external aerial socket how are you proposing to connect to any aerial other than that built in ?
Click to expand...

I'm proposing to use a different radio :)

The point about the walkman thingy is that it demonstrates that a simple length of wire under the side deck doesn't work very well.

Pete
 
prv said:
Would it be completely daft to connect to the chainplate bolt that's behind the radio location, and hence to the rig?
Any other ideas?

Cheers,

Pete
Click to expand...

I'm pretty certain that with FM the aerial has an *ideal* length to get optimum reception.
Our aerial is stuck to the inside of the window, it's about a foot long by about 15mm wide. It works a treat. I can have a look for any manufacturers marks this weekend.
 
You infer that it may finally be a car radio that is going in.
The bolt underneath a stanchion could be good, but I would insulate it from the guardrails if they're not already plastic covered. Big isn't neccessarily better. The other thing that worked for us was the underside of the sprayhood SS hoops.
Things (reception) will no doubt change once you reach your favourite anchorage unfortunately.
Get the proper plug and coax, and just join the centre to the bolt of your choice, and try not to route the coax near too many transducers or flourescent lights.
 
Quite a few years ago now, there were instructions in (I think) PBO for modifying an old Navstar 2000 Decca aerial to provide a preamplified FM radio signal.
Maybe someone here remembers this and has the instructions? I actually have an onld Navstar aerial kicking about somewhere for this purpose but have never got around to finding out what the mod was.

I too have a halfords cheapo rubber duck for mine which lives inder the side deck. It's ok but poor in weak signal areas.
 
I got the impression DAB has proven such a lemon it's now under discussion as to transferring to it; I'd be surprised - and upset - if they do, having bought a DAB and been singularly unimpressed, not least by the power consumption.
 
It's easy to work out the wavelength.
300/Frequency in MHz will provide the wavelength in metres.
So, 300/100=3metres for a full wave at 100Mhz (about the middle of the FM bandwidth and easy numbers)....
Even I can cope with the maths on that :-)
 
Billjratt said:
You infer that it may finally be a car radio that is going in.
Click to expand...

You may have inferred that; I didn't mean to imply it :)

I've always disliked big chunky garish car stereos in boats, especially small boats like mine. All I personally need is an iPod cable and a volume knob, which can be much more discrete. However, my mother requires the ability to listen to Radio 2, so I need to add a changeover switch and a radio of some kind, but again compact, elegant and simple are the order of the day. I think she found the plugged-in portable confusing, and kept flattening its battery by turning off only the amplifier while leaving the radio on.

I'm actually struggling to find a receiver that fits my needs, and am toying with the idea of building one based around a module like this and a PIC for control together with suitable buttons, LEDs, and 7-seg displays. A lot of effort though, compared with just building in something suitable.

Pete
 
Glomex FM/AM antenna

When I got my boat she had a home hifi type FM antenna behind a panel in the cabin, and it was pretty rubbish, especially if I had any instuments on (it was wrapped around the autohelm control computer).

So I bought a Glomex 1.5m antenna, see for instance http://www.tcschandlery.co.uk/10321/Glomex--1-5M-AM-FM-Antenna--RA128-.html and reception has been excellent on both FM and MW/LW ever since. It mounted on a conveniently unused fork of the comms post, down which I poked the coax cable, hence the black tape which covers the hole the coax originally came out from, but I think it could go on a stanchion equally well.

CIMG1502_2.JPG


Bonus point: guess the bird.
 
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