Re: VHF antenna placement question
- From: Larry <noone@xxxxxxxx>
- Date: Sun, 12 Feb 2006 23:44:04 -0500
ace3889@xxxxxx ( Mika) wrote in news:43ee6ec1.17788705@xxxxxxxxxxx:
http://www.metzcommunication.com/manta6.htm
Any suggestions? I am even thinking of using RG-58 coax instead of
RG-213 just to make installation easy ;)
Screw the rest and their hard-wired coax-into-the-epoxy-that-can't-be-
repaired nonsense just to make it cheaper. Get the Metz. Guaranteed for
life. It's what the Coasties use, too.
Bolt the Metz's fine stainless bracket to the side of the mast with the
antenna as far away from anything else up there that's metal. Don't
forget the windvane swing radius...most embarrassing..(c; When you make
up the connector, use two pieces of shrink tubing, one 7/8 size to fit up
against the antenna base to seal the threads, the other one is smaller to
fit over the crimp connection to seal the cable. Leave a drip loop so
water on the cable drips off onto the deck, not runs down into the mast.
Leave a foot or two extra at the mast bottom so you can pull it up the
mast if the top has to be reconnectored later on. Don't make any sharp
corners, especially ones that pull on the cable. Neatness makes RF loss.
Coax cable is made for smooth radius bends, not sharp cornering.
Put another PL-259 connector on the bottom or inside the removable mast
to disconnect the mast from the boat cable for dismasting. For an inline
connector, use two PL-259 male connectors with a SO-239 double-female
barrel connector available from any Radio Shack in between. These can be
replaced anywhere in the world. Use a piece of shrink tubing after HAND
tightening the connectors (no gas pliers to break them, please), to cover
the whole thing. I like to fill the shrink with RTV then shrink it down.
You can slice open the shrink and peel off the PVC next dismasting, even
20 years from now, and the connectors will be as shiny as new, even
laying in the bilge. RTV fill the mast head shrink tubing, as well, to
completely seal up the coax connector on the bottom of the Metz. The
connector looks new after 10 years in the weather that way, and it seals
from the coax sheath to the top of the threads completely.
AS to the RG-58, I have a 5000' reel of surplus military-spec RG-58A/U
I've been wiring ham radio and friend's boats with without problems for
lots of years. 58A has a stranded center conductor that's easier to bend
and doesn't migrate around corners cutting into the poly dielectric.
I'll catch hell for suggesting it's ok to use 58, instead of some exotic
white-covered "marine" crap at $2/ft but Lionheart's Metz Manta-6 is at
55' up the main (another is on top of the mizzen, but is now used for our
AIS as well as the emergency VHF radio with a coax switch). The mainmast
RG-58A/U comes down inside the mast 55', across the corner of the
portside head then through a cable run into the starboard locker. Around
a couple of corners in the locker then aft 25' through a cable run in the
cabinets to the Icom M602 VHF at the nav station by the main hatch. I'd
guess there's 85' of RG-58A/U, total. Must be OK, slightly over-the-
horizon calls to other sailboats is full quieting. I can talk to
Savannah's CG station from Charleston Harbor a hundred miles away to
their high antenna. The attenuation must be awful...(c;
Get one of those little VHF SWR meters off the net:
http://www.walcottcb.com/product_info.php?cPath=23&products_id=920
put two 90 degree coax adapters on it so you can surface mount it right
beside the radio with the right-angle coax connectors going through two
holes back behind the panel. Use a short jumper lead from the meter's
transmitter port to the radio's output jack. The meter is self-powered
by the RF and requires nothing. The little instruction sheet shows you
to switch it to SET and adjust the meter to full scale with the
transmitter keyed (ON SOME LITTLE USED CHANNEL PLEASE NOT 16 OR 22A).
Once set, switch to SWR and a perfect antenna will not make the meter
move off 1:1, a perfect match. There are NO perfect antennas so it will
read something. Anything below 2:1 is fine across the band. Leave this
meter in SWR and note what's "normal" for your antenna on the different
channels you use. A little whiteout band on the glass for "normal" is
nice for the crew. Anytime you use the radio, you can glance at the
meter to see if it's "normal", eliminating those nagging calls just to
see if the damned antenna is still there and the radio is working.
During a real emergency, it's really NICE to know you've got full power
on a good antenna already noted in front of you.
The fancy LCD digital meter on even the finest radios showing you are
transmitting are U-S-E-L-E-S-S!
Unless the Metz is hit by lightning, it'll be there when you need
it....unlike those pretty plastic crap antennas with the unrepairable
broken cables.
73 DE W4CSC.
The 2-meter Metz ham antenna stuck to the top of my car has worn out
EIGHT cars! The VHF Marine one I mounted in the salt spray on a little
jetboat bow is still looking like new from 1997, its new owner tells me.
I lost the whip overboard when I forgot to tighten down the crimp nut
after tuning it, once.
.
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