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-   -   Need advice on VHF install. (http://www.cruisersforum.com/forums/f13/need-advice-on-vhf-install-9002.html)

29cascadefixer 01-07-2007 19:37

Need advice on VHF install.
 
Never done one, and it's getting close to the point in my refurbishing where I have to start stringing wires. Question- what makes a good seal around the coax where it goes through the deck before going up the mast?
Question- do you have to trim the antenna like we used to do for Citizens band.
If these questions sound a little basic, it's where I am at right now.
Oh ! One more thing ! Simple electrical question.You have to run a separate ground for every load in the boat, right ?

Terra Nova 01-07-2007 21:02

Quote:

Originally Posted by 29cascadefixer
Never done one, and it's getting close to the point in my refurbishing where I have to start stringing wires. Question- what makes a good seal around the coax where it goes through the deck before going up the mast?
Question- do you have to trim the antenna like we used to do for Citizens band.
If these questions sound a little basic, it's where I am at right now.
Oh ! One more thing ! Simple electrical question.You have to run a separate ground for every load in the boat, right ?

Yo Fixer,

thru-deck glands for sealing wires are available at any chandler. No need to tune a VHF antenna. Run separate grounds.

best, andy

senormechanico 01-07-2007 21:25

VHF tuning is more theoretical than actually necessary. I stuck an SWR meter on mine one day just for the heck of it, and found a perfect match at the bottom, and about 1.1 at the top.

Re: separate ground, it's not a simple answer. It depends on what you're doing. If you're not sure, contact a good marine electrician.

Steve B. ( Advanced licensed HAM who won't post call sign because of net search engines)

29cascadefixer 02-07-2007 04:31

Thanks , Gentlemen. I didn't tknow there was such a critter as a through deck gland. A previous owner of my boat just drilled a hole, stuck the coax through, then packed the hole with some kind of foam. It leaked ! Rotted the deck and it leached into the support area of my deck stepped mast.
Once again, thanks for the info.

GordMay 02-07-2007 04:56

1 Attachment(s)
Cable Clams:
CableClams - Blue Sea Systems

mike d. 02-07-2007 14:23

as in GordMays post above, or you can get the ones that are chromed bronze?/brass that have a gland nut that you tighten to squeeze a rubber donut you put around the coax

hellosailor 02-07-2007 14:34

29-
In theory I guess you could tune a marine VHF antenna but in practice I suspect they are pre-tuned for best performance either midband, or on Channel 16 for distress use. A good one that is entirely sealed in a fiberglass stick will be sealed, no options to tune it anyway.<G>

More important, buy premium low-loss cable and pay attention to the installation. It really should be supported every few feet in the mast, by tying it off to a low-stretch line if you've got nothing better. If it just hangs by itself, it stretches and the electrical characteristics degrade as it deforms. So if nothing else...get a spool of maybe 1/16" kevlar line and tie it every foot or two, to take up load off the coax. Make sure to use a drip loop at the top, to keep water from running into the cable.

And silicon grease inside the cable fitting (to prevent water intrustion) and something like butyl tape or coax sealant OVER the coax fitting, also to keep water out. Those 2-3 things may add $10+ to your installation--but a cable that stays unstressed and bone dry, can last a very very long time. Much cheaper than going up the mast every couple or five years to run a new one.<G>


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