On Fri, 08 Dec 2006 19:02:42 GMT, cavelamb himself
wrote:

krj wrote:

Might make a good mizzen mast?
Unstayed???

There is a good calculator for coax losses at

http://www.ocarc.ca/coax.htm

A 25W VHF at 156 mhz with 40 ft of RG-58 will have 15.819W at the
antenna. With RG-8X it will be 16.741W. With RG-8U it will be 19.859W.
Assuming a VSWR of 1.3

Like many people have said, 15 or 20 watts and you cannot hear the
difference. It is antenna height that matters as far as range is
concerned. Masthead installation means antenna us way up, but hard to
fix if something goes wrong. And most likely extra connectors, as you
would need to detach the antenna when you take your mast down.

My VHF antenna is only some 3 meters above deck. Permanent
installation and therefore less maintenance problems. Coast guard
stations 20-30 nautical miles away come in strong since they have
antennas way up in tower, and I can hear and work anything within
visible horizon. If you dont go far offshore, this is enough for
emergency communcations etc.

Well, considering all aspects of this, RG8 foam core - WELL SEALED
might be the best choice for me.

Foam is great for fixed installations such as your ham radio antenna
at home. But I wouldnt use foam for boating installations. Any bends
etc, and center could eventually short circut with shield.

Now, how to seal up the connectors?

Adhesive lined heat shrink may be fine for the top one, but the
deck connector? That one has to come apart occasionally.

I used just electrican´s tape with masthead antenna installation on my
previous boat. Takes is few minutes to seal up in spring and take off
in fall. If connectors corrode, you can clean the surface or even
replace them every few years. Leave somewhere a few extra inches of
cable so you can replace connectors.

But make sure you seal cable and connector so that water will not
enter cable. Its not a disaster if contact surface corrodes a bit,
but any leak and coax will be filled with water. Still OK to your DC
meter, but water in cable spells very high losses in HF and VHF,
nothing like in line loss calculations when different cable types vere
compared. Cable filled with water is better thrown away.

Mika






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