co-ax for v.h.f

[mickshep]

Am in the process of re wiring the boat ready for the off. the co-ax cable which runs inside the mast is in a pretty bad way. I have looked at some some cable in one of the local chandlers and to be honest it appears pretty cheap 'n' nasty. I have on the other hand access to a length of the co-ax used to connect my computer to the broad band system, which in my ignorance I assume will be of very good quality. Is this likely to affect the performance of the Sailor RT 2048 if I use this cable instead??? Cheers in advance. Mick

<hr width=100% size=1>

 

[tome]

Mick

Careful here because coax is characterised by impedance (amongst other things). VHF coax is 50 ohm, but my broadband connection uses 75 ohm so would give a mismatch and a loss of power. Worse, it could reflect power back into the output of the set possibly damaging it.

If you need to get some coax for your VHF ask for RG58 which is widely available, and go for tinned rather than bare copper. Try <A target="_blank" HREF=http://rswww.com>http://rswww.com</A>

Regards
Tom

<hr width=100% size=1>

 

[snowleopard]

also

vital to keep it dry- water wicking into the braid will kill transmission so make sure you seal carefully at the masthead joint.

<hr width=100% size=1>

 

[mickshep]

Cheers Tom. I've dug out the spec' on the V.H.F and it is 50 ohm as you suggested. the cable is IG11, how do I find the impedence for this co-ax cable? The only printing on it is; 2002 COMMSCOPE 228656m. 'Fraid when it comes to comm's I can use them no bother, but my understanding of the setting up goes only as far as setting the tension in the string between the two tin cans;-)D Cheers, Mick.

<hr width=100% size=1>

 

[tome]

Mick

All Commscope Broadband video cables are 75 ohm so not suitable for VHF (just checked their site (<A target="_blank" HREF=http://www.commscope.com/html/network_coax_broadband_video.shtml>http://www.commscope.com/html/network_coax_broadband_video.shtml</A>)

Stick with RG58 which has acceptable losses and impedence match, and minimise the inline connectors. If you need to fit them for mast removal, make sure you wrap them well in self-amalgamating tape which will prevent killer moisture from penetrating.

Regards
Tom

<hr width=100% size=1>

 

[mickshep]

Thanks Tom. Will go for the stuff you've recomended. Cheers Mick.

<hr width=100% size=1>

 

[Piers]

Hi - Must use 75 ohm and must be the best quality you can find. When cabling, try not to have any connectors except for the cable to the aerial - each connector adds about a 3dB loss in signal strength.

<hr width=100% size=1>Piers du Pré
http://www.dupre.co.uk

 

[tome]

Hi Piers

No, use 50 ohm not 75

Regards
Tom

<hr width=100% size=1>

 

[vyv_cox]

I prefer to put connectors for mast removal below deck. Take the cable from the mast into a gland with a compression fitting, induce a short downward loop so that any drips fall off rather then running into the fitting, then cut and install one of the solderless connectors sold by your chandler. My experience of self amalgamating tape is that it sticks to itself but not much else.

Incidentally, on the deck glands I don't bother with the O-ring, chuck it away and put a dollop of Sikaflex in instead. Never leaks and doesn't degrade like O-rings.

<hr width=100% size=1>

 

[tome]

Vyv

Can't agree with you on self-amalgamating tape, if used correctly. We rig and de-rig nav and comms equipment daily in some of the most inhospitable regions of the world and use it as a matter of course. I recently de-rigged a GPS antenna which had been in place for 3 years on the chimney of my house (I use it for data gathering). Once I'd removed the tape, the N-type connector was as new even though the antenna was looking decidedly old and knackered.

Maybe you aren't stretching it enough?

Regards
Tom

<hr width=100% size=1>

 

[vyv_cox]

Tom,

It could be I'm not giving it a fair trial. The roll I have came with my first cruiser, 1988 I think, probably not new then. It didn't work when I first had it so I put it in the tapes and adhesives box, where it lies to this day. I tried a bit a couple of years ago and it was no good. No staying power.

Vyv

<hr width=100% size=1>

 

[ean_p]

mmmmm second only to tie-wraps on list of simple but marvelous....stretch it 'till it nearly breaks though!!

<hr width=100% size=1>

 

[Piers]

Oops - apologies. Just got back from two days on the boat.

50 ohms is right (was I reverting to TV days?). And if I'm right this time, it's RG-8 or RG-8X cable.

Piers du Pré
http://www.dupre.co.uk

 

[petery]

... co-ax for inmarsat-c .. advice please

I bought a Trimble Inmarsat C unit on US e-bay for 'next to nothing' . I have tested it and used it on shore and it works fine. --- but it must have come off a battleship as the coax isabout 18mm in diameter!

I am about to install on the boat and will have to thread the downlead through some 25 mm tubing and even smaller holes. Can anyone recommend a thin low loss 50 ohm cable that won't lose too much signal at Ghz frequencies.

<hr width=100% size=1>

 

[Strathglass]

Re: ... co-ax for inmarsat-c .. advice please

Peter
I have some Andrews heliax semi rigid and usable but not precicely compatable connectors. It is about 8 -10 mm od and would be good for Ghz. What length would you require?. I would swap it for a similar length of normal 50 ohm coax suitable for 200 watts HF plus the carrage.

PM me for further details

Iain

<hr width=100% size=1>