Mast Wiring

[bedouin]

I've only owned Bedouin for 4 years, so haven't got round to completing all of the tasks on my original To Do List yet (and if/when I have it will probably be time to sell her )

My current problem is with the wiring that goes up the mast. This is not of the best, with none of the wires in question being tinned and all the connections at deck level using the old metal connectors that are not 100% waterproof.

As a result I have significant oxidisation both of the plug/socket connectors themselves and the wires, so the connection is intermittent at best.

I suspect the only really satisfactory solution is to replace the lot - which leads to three questions

(i) Given that I would rather put this off until the next time I have the mast down, is there any feasible way to clean up the oxidation to improve the contact in the interim? (Brasso does a good job on the pins of the plug, but is less use on the socket and none at all on the wires

(ii) When I get round to replacing the connectors are any of the modern ones better than the old metal ones I have now?

(iii) is SWR a reliable way of measuring the quality of the VHF connection (for that matter is it likely that VHF will couple capacititively across a poor DC connection)



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[Benbow]

>clean up the oxidation.< Not much in my experience, emery paper will help.

> replacing the connectors < I would advise sending the wires down through a waterproof gland and making the connection inside the boat. For VHF aerial I would recommend sending the wire through the gland and plugging straight into the radio with no other connection. You can get glands that allow the connector to pass through so you can remove the mast without problem. This is the only way to avoid constant grief from deck plugs.

>SWR a reliable way....< Yes, an SWR meter is THE way to test that your radio's output is being radiated by the aerial.


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[john_morris_uk]

Re: SWR Meter

Sadly the SWR meter WILL NOT tell you that the signal is being radiated from the antenna. It will only tell you about the match/mismatch at the point the SWR meter is inserted in the transmission line.

In fact one of the ways of measuring the loss of a transmission line is to short or open circuit the far end and with a suitable RF source monitor the mismatch. In a loss free line the SWR would be infinity to one, but this never occurs - the difference is loss in the line and there are tables to calculate what the loss is. Don't try this with your VHF radio - I said suitable RF source!

The point is that a very lossy line will give an apparently 'good' match with a correspondingly low SWR. What is really happening is that your RF is warming up the cable!! Only if you are certain that the coax is in good condition will a low SWR will indicate that the RF is probably being radiated... Sorry to be a pessimist, but the other possibility is that it is gently warming up the faulty matching unit in the antenna... The latter is unlikely but I have seen it happen.

Regards John

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[Chris_Robb]

You may be able to get away with cleaning up the plugs, however if the copper wire has gone black its rather terminal. I had conventional pinned plugs like you which were corroded like yours - they cleaned up ok, and using self amalgamating tape - they were made 100% waterproof.

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[tome]

There's one trick I use for cleaning blackened copper wire. Use a Stanley blade to scrape it bright, working your way patiently round the wire. It should buy you time until the mast has to come down.

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[roger]

I reckon deck plugs are inventions of the devil. They mostly leak into the plug body and rarely seal pin-socket.
Try www.elavabro.com for a low profile swanneck type deck gland. You can join the aerial lead with a suitable BNC connector inside the boat (with some signal loss) All other connections can be made fairly simply. Having a long enough cable to reach the radio may well be difficult hence my suggestion of a connector.If you can do it in one length thats much better.
Peyton has a cartoon showing mast lifting pulling out all the cables!!

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[Gunfleet]

I developed my own system for bullet proof connections. I put a longish piece of heat shrink over the cable, crimp the cable, heat the shrink enough to close it up and form a sort of long cup over the jointed cable. Next I make up a bit of epoxy and syringe it into the cup. Once that's set I finish the heat shrinking. That old chap don't leak. After all this invention Tome told me that epoxy coated crimps exist and you could just heat shrink over those. Grr. I'm sure he'll pass you the address of the makers. Either way once this is done you will have lost the ability to simply disconnect the cable - you'll have to cut it or heat it enough with a gun to get the epoxy gooey. But this is a lot less inconvenient than you'd think, and certainly a lot less inconvenient that a mast light which goes on the blink in a seaway. Best of luck with it, John
ps for the more literally minded - I am not recommending this procedure with the antenna cable.

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[tome]

The glue-filled terminals are available from RS see <A target="_blank" HREF=http://rswww.com/cgi-bin/bv/browse/Module.jsp?BV_SessionID=@@@@0360011709.1079371700@@@@&BV_EngineID=cccdadckmeilijecfngcfkmdgkldffl.0&cacheID=ukie&3256824849=3256824849&stockNo=465716> here</A>

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[Gunfleet]

less than 1/2 hour! NM

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[AndrewB]

Deck plugs.

No type seems really satisfactory for long-term use on deck, even the so-called waterproof ones, however well taped up. Sea water penetrates, eventually the copper wire goes black and rotten. I switched over to glands, with a junction-box beneath the mast for the connections, and since have had virtually no problems.

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[bedouin]

Re: SWR Meter

As I understand it the SWR meter will indicate an impedance mismatch between the VHF and the antenna and cable. So if there is a bad connnection /discontinuity at the deck connector then that should register on the meter, assuming the wiring in the cabin is in reasonable condition (as it probably is).

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[MainlySteam]

Re: SWR Meter

Measuring SWR with the cable open or shorted is not a useful method of measuring transmission line losses as the SWR meters available to us are totally inaccurate at more than low SWR's. As long as the antenna is an approximate match to the cable, as it will be if it is not damaged, the SWR meter will give a satisfactory indication of the condition of the cable with the antenna attached.

Without changing anything, if you measure the SWR and it is ok, then you can be pretty confident (but not totally so) that both the antenna and the coax are ok.

If that is not so and if there are any doubts about the antenna then the easiest way to check the coax/connectors is to place a 50 ohm 25 watt min. capacity dummy load in place of the antenna and measure the SWR at the radio. If you have not access to a dummy load then see the end of the next step.

If the coax checks out doing that, but the SWR is high when the antenna is reconnected, then the antenna can be checked by taking it down and connecting it directly to the VHF and SWR meter with short coax patch cords (can be bought made up and you will have needed at least one in order to connect the SWR meter to the radio) and a brief test transmission made (don't touch the antenna when transmitting, it will burn you, and make sure it is clear of metal objects). If you check the antenna first, and it checks out, then it can be used instead of the dummy load in the step above.

In all the measurements mentioned above, you should expect the SWR to be between 1:1 and around 1.5:1 and if so you can be confident in the system.

If anyone comes along and tells you that the SWR will vary depending on the length of the coax, tell them to go away. Get rude if they insist /forums/images/icons/smile.gif.

Alternatively, you might find it easier for someone to do it for you.

John

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[LadyInBed]

Re: Mast Wiring (i)

<A target="_blank" HREF=http://www.rustoff-int.com/healthandsafety.php> Biox </A> is the stuff you need for removing verdigris.

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[Aeolus_IV]

I'd recommend moving all of the "joins" inside the saloon - it easy enough to get the glands/deck seals which will allow normal sized plugs through. This is how Aeolus is set up - no trouble with water in the connectors or leaking through the coach roof. Of course, this assumes that there is sufficient slack to allow you to do this. One of the problems with getting water into your plugs/sockets is that it will track along the cable, so you may find that corrosion goes further than you thought.

Jeff.

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[bedouin]

I'm considering that - but one of the problems is that without a reliable way of cleaning the corrosion from the wires I daren't touch the connectors. My guess is that by now the oxidation extends a few feet up the cable so if I remove the existing connectors then I may find it difficult to make a reliable connection inside the cabin - l only have a matter of inches to spare.

The Biox stuff Nigel mentions sounds very promising - I might see if I can get my hands on some and see if that cleans up the oxidation.

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[Benbow]

You don't need to worry about that. Hack it back as far as you possibly can. Leave a 'tail' of bare cleaned wire at least 1 inch long, solder in an additional length, seal that with plenty of the adhesive-containing heat shrink stuff that was mentioned previously. Ignore the people who will tell you that soldering makes connections brittle, it does but it won't cause problems on an 'inline' joint properly supported by heat shrink. To really give physical strength you could bind the whole lot in self amalgamating tape.

None of this of course applies to the VHF coax - there you are probably stuffed !

HTH

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[EdEssery]

You are right about the oxidation running a long way through the cable. I rewired my boat over the winter because I had had a number of electrical problems and all the exposed copper I could see was black. For interest's sake I stripped all the insulation of one length of cable I removed (about 10 feet) that supplied power to some of the internal cabin lights - it was oxidised along its entire length. The boat was built in 1986/87 so the wiring was 17 years old.

Ed

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