AM/FM antenna - what on earth is this?

[tiger79]

I specified my boat with a factory-fitted Fusion entertainment audio system.  The sound is good, but the radio reception is lousy.  Today I finally bit the bullet and traced the antenna wire from the Fusion controller.  It goes through the heads compartment, through the port cockpit locker, and into the space under the back of the cockpit.  In there, it disappears up behind the gas bottle locker.  I can't see it or touch it, but with my phone I was able to get a photo of it.  It goes into a metal thing, probably about 3cm square, which is fixed to the rear bulkhead of the cockpit locker.  There's nothing on the other side of the bulkhead.  What on earth is it?  There are three screws, I guess one holds it to the surface, what are the other two?  They look loose - do you think something should be connected to them, to form a dipole antenna?

Any thoughts would be very welcome! Alternatively, if I were just to connect another antenna to the Fusion unit, what would you suggest?

[tiger79]

So 30 people have looked at the pic.  Doesn't anybody have any ideas?

[Yngmar]

Hmm, let's see.

* The fibreglass around it tells a clear story: It was there when the boat was built.
* It's connected to your Fusion controller
* It's labeled in German, something about RG cable
* And also "Achterstagklemme" = backstay connector

Presumably it was supposed to be connected to the backstay. Does your boat have an insulated backstay that can be used as an antenna? If so, it wasn't connected to it, perhaps because at the time the radio was fitted, the rig wasn't on yet. Perhaps someone forgot to rig it with an insulated backstay and the radio fitter considered this an OPP (other people's problem). Something like that :-)

Unless you have an insulated backstay, a simple car stub antenna should do the job, and does not have to be mounted outside. Inside, away from electronics and larger metal bits should do fine.

[tiger79]

* And also "Achterstagklemme" = backstay connector

Ah! Now that makes more sense.  Thank you for the translation.

The boat has a split backstay, with a block and tackle on the port side. I initially wondered whether the antenna cable was connected to the U-bolt which the backstay is attached to on the port side, but that the block and tackle prevented the backstay working as an antenna.  I may try connecting the antenna cable to the starboard U-bolt, which has metal-to-metal contact to the backstay.

I reckon your theory about the fitter thinking it was an OPP is correct, but it was a bit odd for him to just screw it on the bulkhead out of the way!  Not the German efficiency we expect!

[Yngmar]

Unless the backstay has insulators fitted (like in a SSB installation), this won't work very well. At least on my boat, the backstay is connected to the mast, which is connected to the keel with a big fat copper rod, so lightning strikes can leave the boat that way rather than making a hole. This grounding would however make the rig (including backstay) a very poor antenna.

Might be your lower backstay section is insulated by way of a plastic sheave in the turning block or something though, or perhaps there is no mast-to-keel connection.

[tiger79]

Good thought, I imagined the sheave at the top of the mast may be plastic, but I could be wrong.  I'll have to check continuity between backstay and mast.  The mast is certainly earthed to the keel with a beefy cable.

[Holger]

While I may help with the German words on the label I am afraid that I can't help more: The label reads (to the extent I can read it)

OPTION BY ANTENNA CABLE (ANTENNENKABEL) RG 58 + BACKSTAY CONNECTOR (ACHTERSTAGSKLEMME)

[Stockie]

So where does the radio aerial normally go?  I have an older B37 2006 with an aftermarket fitted Fusion 650. And the reception is pretty good.  I have recently fitted an AIS with an aerial splitter, and this device includes a BNS spur for hooking up your AM/FM
I am thinking of hooking it up for fun, that will get me a mast head aerial. 
Tiger, do you have an AIS?
This may give you an alternative to wire up your aerial!
Cheers Richard

[tiger79]

So where does the radio aerial normally go?  I have an older B37 2006 with an aftermarket fitted Fusion 650. And the reception is pretty good.  I have recently fitted an AIS with an aerial splitter, and this device includes a BNS spur for hooking up your AM/FM
I am thinking of hooking it up for fun, that will get me a mast head aerial. 
Tiger, do you have an AIS?
This may give you an alternative to wire up your aerial!
Cheers Richard

No idea where the factory were supposed to connect the aerial!  I've made a simple dipole aerial with wire and stuck it in the cockpit locker; this gives reasonable reception.  I'm considering an aerial splitter, but I really don't like the concept.  My AIS is integrated with the Garmin VHF.