Changing a masthead VHF antenna

fastjedi

fastjedi

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Been down to the boat today (Port Solent) for 'final commisioning' before going back in the water on the 20th April. The VHF will only work on the emergency antenna. On investigation it looks like antenna is a "ex antenna"! I am reading 9.6K ohms at the base of the mast :-(

Talked to a Rigging Co today who said ....
1. Can't do it ashore (Port Solent) for insurance reasons (fair enough)
2. Won't do it afloat (Wicormarine) because it is too difficult to get to the island pontoon
3. Can't fit you in till June anyway!!!

Where do I go from here?
1. Antenna on the pushpit to buy me some thinking time?
2. Invest lots of ££ in a Top Climber and DIY?
3. Anyone know a freelance rigger I could employ for an hour or two?

I have been up as far as the decklight using my bosuns chair ... but was able to scramble up most of the way ... The angle to get the main halyard off the coachroof and onto a primary winch is not good.
 
Use an ordinary ladder to get up your mast. Use a topping lift to pull your ladder up and make secure.

High gain aerials are good for those occasions when anchored in marginal (radio) locations. Our resident experts will tell you all about take off angles with high gain aerials, which will all be true while sailing.

Your problem sounds to me like the coaxial cable has become moist. Now this one is guaranteed to get our experts going, ever wondered about drying the coax out ?

A few amps up the cable for an hour or so MAY do the trick, at least temporarily and or until civilisation is reached. What have you got to loose?

73s de

Johnth
 
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Hi
If you want me to pop up the mast in the morning just send me a message. I just shinned to the top of my s38 mast to replace my aerial mounting bracket this evening - and that was a 47 foot mast. The aerial appeared to be saggins. I also have a spare Hawk antenna sitting next to me on board in Southsea marina - in case you needed anything to swap with.. and three aerial cables!!!
You don't have to accept - but I used to get to the top of my Sun Odyssey 29 mast.. and can do this current 47 foot mast in about a minute..
PS - weighing less than nine stone might help and I don't need to be pulled...
Regards Martin... PS - I'll measure the resistance across the aerial plug on mine now.. and see what the value is..
 
Wow, that is impressive Martin. Once upon a time I weighed about the same as you do but could not get any where near to matching your time to ascend.

Of course, yours is the best suggestion for a proper fix.

Night
73s de
Johnth
 
Well - the V-Tronix Hawk instruction leaflet says there should be a 10k ohm resistance between the inner and outer sheath.. very close to your measurement.
I have just measured infinity across the lower end of my masthead cable (with two different digital ammeters) yet it seems to be working fine.
 
I have just re-read that you are out of the water... it's been done (to the top of the mast whilst out of the water at Camber Quay).. but sounds like Port Solent are not happy with that.

Next time I'll time exactly how long it takes.
 
I have just measured a brand new Hawk antenna with 20m of new cable - 10.08 k ohm.

I am now wondering if my (older) aerial is a different type. Someone will come along later (I hope) and say that some aerials do appear as open cct.
 
I'm still thinking!.. Did anything change? And is there a connection at the foot of the mast (or in the cabing ceiling) that ought to be checked first?
 
Mast top antenna

Yes all the connections especially at the base of the mast should be checked for condition by dismantling.
I get good results from a pushpit mounted antenna so would advocate same as an emergency anttenna.
good luck olewill
 
Mmmm ...... so 9.8K ohms may not be bad after all. There are BNC connectors at the bottom of the mast (outside). I dont think this is the problem though ...
1. They are shinny and probably date back to the standing rigging change in 2008
2. They were dry and well protected with self amalgamating tape
3. I have taken them apart to check they were properly fitted. They look fine

From there to the radio is RG58 .... again, probably not ideal, but probably O.K?
To clarify the issue, the only channel I can hear is 80 (Port Solent) and many radio checks to them resulting in no response! .... and an immediate response once the emergency antenna was fitted.

Looks like a bit more investigation is required before asending the mast?
 
If you need to replace the antenna, with the same type, it could be easy and done with a bosuns chair - I am sure you could get a couple of people in the marina to take you up, and if you havn't got one I am sure a lot of boat owners carry one, if not the yard.

However, having just done my V-Tronix (mast down) on an antenna which was maybe 12 years old or so - the coax connector (at the antenna), and the mast bracket were very slightly different, so it meant that the bracket and cable needed changing as well. Straightforward with it on the floor. May take a bit longer with the mast up.

However if your cable and antenna look physically in tact then indeed the connectors should be the first priority.

The decision to rig up a shorter range temporary option really depends on how far from civilisation you will be going. If you are reasonably close to shore mobile phone may cover you for emergancy services if necessary, but not further out.
 
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