Navtex aerial

[BigLes]

I've inherited a Lokata navtex with the boat we recently purchased. It's an older printer version than runs on the 518 frequency only. I've had trouble picking up stations and was suspecting the active antenna. Having read the manual I took it's advice and rigged up the backstay as an aerial and it recieves Ostend, Niton and Corsen OK (although no weather forecasts even though it was set for all stations and all message types).

My question - is it OK to leave the set-up with the backstay as a pemanent aerial? Bearing in mind it will only be recieving a signal (no transmissions). If so, why would it have had an active aerial in the first place (which is at the top of the mast next to the VHF aerial, which I understand is not the best place for it!).

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[iangrant]

Les
I'd leave it on the backstay, but wound round a few times wire unstripped as inductive, rather than directly connected.
Forcasts seem to come in at strange times, loads of nav warnings stream in all the time..

Active aerials? maybe for little motor boats?


Ian



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[BigLes]

I was thinking of attaching it on the inside of the boat where the bolt for the backstay plate is attached to the deck.

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[iangrant]

That'll work but I think the danger with a direct coupled is blowing the c**p out of the box ground shifts, electrical faults etc.. or in a thunderstorm - doesn't have to be a direct strike..

Ian

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[BigLes]

Couldn't I have an in-line fuse?

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[iangrant]

Dont think so - you'd lose signal bits I think - perhaps a radio engineer could jump in here..

Ian

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[Benbow]

Well I am no electrical engineer, but.

If you have a lightning strike a few mls of insulation will be highly unlikely to have any effect, neither will a fuse. If you think about it the lighting has jumped a very large (albeit ionised) air gap to get to you, a bit more won't bother it.

You will get better reception if you directly connect to an insulated backstay and have a separate ground connection to something in contact with the water. An uninsulated backstay on a plastic boat will be unpredictable.

A simple alternative is to run a wire (complete with its insulation) up the rigging, that way you can bring it down if lightning threatens (so a strike will only blow a hole in the bottom of your boat and not damage your navtex (until the water reaches it))

Not sure what other surges might arise in the rigging capable of damaging your set, except RF and that will be unaffected by the insulation.

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