VHF Antenna ???

[rosamaldon]

The mast is down and the new DSC has arrived. The course is booked but the antenna is looking it's age , don't we all!

Are antennas just plain and simple and much of a muchness or are some better than others ?

Most of the sites I've visited extole the virtues of this brand of radio as opposed to another but not much is said about the make etc of the antenna.

Having had signal problems recently with the Coastguard reporting that we had an antenna problem and having had to talk to them via mobile phone on the occasion of needing our friends from the RNLI I'd like to fit the best mast head mounted kit possible.

Some pointers would be appreciated.

All hail to the crew of the Walton on the Naze lifeboat.



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[sailorman]

welcome to another East Coaster
WOT no Bio who r yer
roger



<hr width=100% size=1>Mines a Crocodile sandwich & make it Snappy

 

[bruce]

there are 2 basic types, long glass rods about 8' long and norm on powerboats, and the base loaded antenna that has a wip about 18 inches long mounted to a can/loading coil at the base and usually mounted on top of mast. the longer ones are better, but not suited to sailboats. unlike radios, antennas are very basic things, basic either one or other, there are no tricks that would make one better than the other. i know ham radio people will take exception to my comment because we can do better, but in marine world you have to use what ya got. KD4NKL.

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[Oldhand]

<antennas are very basic things>

I used to be paid quite well designing and developing antennas and people like the armed forces spend millions on them. Pleasure boat antennas may be basic but antennas in general - I think not.

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[Joe_Cole]

I suspect (and I'm not an expert) that to all intents and purposes one VHF marine aerial will be much the same as any other. What seems to be more important is that all the connections between the aerial and the radio are top notch. As thats usually where the DIY bit comes in, that's where the problems start.

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[colin_jones]

Have a look at the Vitronix antenna designed for RIBs. It is short enough to be practical, but the 'helical' wind makes it a good, low windage performer.

I have had one at the masthead for 3 years and am still pleased with it.

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[Talbot]

I replaced mine a couple of years ago with a <A target="_blank" HREF=http://www.seamarknunn.co.uk/catalog/items/item267.htm>V-Tronix Hawk</A> which also includes the wind indicator. Great piece of kit, with much better range than its predecessor

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[fireball]

Same as we've got ... but _apparently_ there is a problem ... namely when a s*dding great big bird decides to land on the wind indicator and either bends it or snaps the antenna clean off ... mind u ... at least you get a trip to the top of the mast to replace it!

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[Piers]

For a GRP aerial, I would always choose Shakespeare. I have no working knowledge for a whip-style aerial.

Given you have a yacht, I wouldn't choose more than a 6bD gain aerial, maybe even less.

Cabling is critical. If at all possible, keep it to a single length of cable between the aerial and the radio. For every connector you will lose 3dB gain.

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

 

[pvb]

Go for a S/S whip antenna...

Your best choice for price and performance on a sailboat is a straightforward stainless steel whip antenna. Most common make found in UK is probably V-Tronix, and their products are good. Most whip aerials are about a metre long and are rated at 3dB gain. Longer fibreglass aerials (as often seen on powerboats) may have a greater gain figure quoted, but the pattern of radiation with a longer aerial is flatter - this is OK on a powerboat, but no good for a heeling sailboat. I'd steer clear of the "Hawk" type, as they are more prone to damage. I replaced my masthead aerial about a year ago with a plain V-Tronix whip after the previous Hawk type had been broken.

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[Talbot]

So it was you who started the story about big bird needing glasses? /forums/images/icons/smile.gif

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[Salty John]

The most common in the USA is the Metz. Very compact, robust, all stainless and used by the US Coastguard. The Metz antenna has worked well for me on my last two boats. Don't know where they are available in the UK, but West Marine in the US stock them.

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[gjeffery]

I have a base loaded stainless whip at the masthead. It seems to work well enough, but I have a lingering concern about the connection of the coaxial cable to the antenna base. The "connector" is a push in type. The coax cores are stripped back, passed through a waterproof sleeve, then a clamping bolt, and pushed into the antenna base. The clamping bolt is then tightened into the base, and the signal connection is made by the thin central conductor being pushed into a small socket that I cannot see. This requires an unusual act of faith.

I will ensure that any replacement antenna has a more positive connection using a standard VHF coax plug/socket.

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[rosamaldon]

Thanks ,

Aluminium mast .. presume must use aluminium rivets , I did hear of something that I can coat s/s self tappers with to prevent (??) corrosion when used with aluminium masts. Any ideas.



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[dickh]

You should use MONEL pop rivets, particularly if fitting stainless steel to aluminium. Coat the rivet and the interface between the two metals with DURALOC - this insulates the dissimilar materials. Monel rivets won't react with either SS or Al. But they are harder to 'Pop' when using a hand riveter. Don't use aluminium rivets - they aren't strong enough and the central steel bit always rust!
Good luck.

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[DavidTocher]

You shouldn't lose anything if proper connections are made.

I suggest using a BNC plug on the usual coax supplied with masthead antennae. The big advantage is that it can be installed through a deck mounting without removing the plug. I can't remember the supplier but it consists of two parts; a ring screwed to the deck and a removable ring which squeezes a split tapered bung when fastened down to the deck fitting.

I get zero SWR with one BNC to BNC inline connections and a PL259 plug to SO253 socket on the rear of the radio.

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