FM Radio antenna

[Peter123]

My Jeanneau SO 36i came with an FM radio CD player ready fitted. The radio reception is very poor and I think that the antenna is the problem as the radio seems to work better with an ordinary piece of wire jammed in the aerial socket on the back than with the antenna connector that it came with.
The difficulty is that the antenna cable that came with the boat disappears beneath all the wires that connect with the switch panel and I am unable to follow where it goes to and therefore I cant work out if and where it has been damaged. Does anyone know where the antenna is located and what sort of antenna it is? I think the cable that came with the boat is probably an aerial extension lead which may run to an antenna located somewhere up forward in the boat perhaps under the headlining.
Thanks.

[Zanshin]

I found my factory antennas on my 43DS and on the 49DS right behind the breaker panel/chartplotter. The one on the 43DS was a car antenna. Both were horizontal and radio reception was, as one might assume, pretty shabby.

[Don Reaves]

My SO35 also has problems in this regard. I considered adding an amplified antenna until I realized that I already had one. The biggest improvement I have made in radio reception is to turn off the battery charger while we listen. (We spend a lot of time plugged in.)

Don

[j]

on a late 2008 36i it is behind the switchboard on the underside of the small shelf (the shelf between the switchboard and chartplotter mounting area)

A picture of the antenna is attached.

[Peter123]

Thank you.
This is helpful.
I've also found that the radio picks up a lot of interference from the charger and from the diesel heater.
If the antenna is situated behind the switchboard (and I still cant find it), it would explain why it works so badly. there must be more electrical noise here than almost anywhere on the boat.
As the other wiring is such a jumble, I'm going to try connecting a screened aerial extension lead from the FM radio into my AIS aerial splitter and hopefully will then have the FM getting its signal from the masthead antenna.

[pj]

If you have a TV antenna (Glomex or equivalent), buy a splitter and you will get great FM. AM will suffer

[j]

Dec 8, 2010 17:14:21 GMT Peter123 said:

Thank you.
If the antenna is situated behind the switchboard (and I still cant find it)

I had the switchboard out again tonight so I took a photo (attached), hope it helps.

Photo taken from the chart table (pushed forward) looking up into the distribution panel area.

[Peter123]

Thank you very much for this.
Mine isn't in the same place and my wiring is not as tidy as yours, in fact mine is a complete dog's breakfast, but at least I now know what I'm looking for.

[intruder]

Use your VHF antenna with something like this:

www.sailgb.com/p/antenna_vhf_fm_splitter/

or the Shaespeare splitter

[Peter123]

Found it at last!
Almost exactly where J said it was but a little further aft.
In fact, only about 15 cm from the back of the radio.
I've connected a new shorter screened lead from the FM to a VHF splitter. Now I have near perfect FM reception even when the battery charger and Webasto heater are on.

Thanks to all.

I don't know if Jeanneau High Command or their dealers follow this forum or see feedback from customers as a help or an irritation but anyway, if they do, they might consider the following:
An FM antenna should be mounted as high as is reasonably possible
An FM antenna should not be mounted near sources of electrical noise
It seems that several (probably many) Jeanneau owners get poor reception on their FM radios, and some cant listen to the radio when the battery charger is running.
The Antenna wire supplied on my boat was 2 metres in length, but this length was used up by it running randomly around behind the switch board before ending about 10 cms above the radio.
It would be difficult to have put it is a worse position.

[so40gtb]

My "day job" is the transmission facilities engineering director for 41 television stations, so I have many years of experience with VHF/UHF transmission and reception issues.

Height above water is everything when it comes to VHF-FM reception, VHF-TV as well.

On my boat, I use the Shakespeare VHF-FM splitter box to interface the masthead VHF whip to the FM receiver and communications transceiver. It works well enough, isolating the FM receiver from the marine radio transmitter. There is some loss in the box, due to both coupling and mismatch, but that's overcome by the height advantage of the masthead whip. This is a far less than ideal solution, but it is simple, economical, and takes minimum time and hassle to implement. I have no issues receiving stations whose transmitters are located 70 km (45 miles) distant. There seems to be no significant impact on marine radio transmission, but I'll quantify that by detailed measurements during spring commissioning, now that I have a sufficiently portable network analyzer to use in characterizing the antenna and interconnecting components.

Caveat: Nearly all FM transmission in North America is circularly polarized, so vertical or horizontal antenna elements (ideally) do not produce substantially different results. In Europe, horizontal polarization is more prevalent, so vertical whips won't work as well, due to cross-polarization loss.

A different approach would be to install a horizontal dipole between the mast and the shrouds (obviously insulated at the latter), but that would have the usual dipole directivity (less sensitivity when the direction to the transmitter is abeam - like rear window embedded horizontal dipoles in cars).

Or one could install a separate monopole antenna atop a spreader, but that would also have a directional reception characteristic because of interaction with the mast and shroud and the lack of a uniform ground plane in all directions (an interesting numerical electromagnetics modeling project, though, which I should do some day).

Absent a mast-mounted antenna, a horizontal dipole embedded athwartships in the cabintop, between liner and fiberglass, is probably the best option. A "twin-lead" 300-Ohm dipole antenna will do. Separate it at least a meter (or yard) from the traveler. Match it to the coaxial line going to the receiver using a 300:75 Ohm balun.

--Karl