" JimH" jimh_osudad@yahooDOT comREMOVETHIS wrote in message
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"NOYB" wrote in message
ink.net...

"Shortwave Sportfishing" wrote in message
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On Fri, 13 Jan 2006 23:35:25 GMT, "NOYB" wrote:


"Wayne.B" wrote in message
m...
On 13 Jan 2006 09:56:30 -0800, "
wrote:

According to post in this newsgroup, we need a metal plate for
grounding if we use a 3dB antenna, and a fiberglass boat doesn't have
it. My boat is a fiberglass boat. What's the alternative? Does this
mean that I cannot use 3dB antenna?

There is no need for a ground with a VHF antenna.

Either the 3 db or 6 db antenna will be adequate for near shore
coastal operation.


I'm with Wayne on this one.

The dB rating plays a relatively minor role in the distance the signal
travels. The height of the transmitting antenna plays a larger role.
But
the height of the receiving antenna is the most important element.

Example:
A 3' antenna mounted on the top of the gunwale of a small boat might be
5'
above the water line. It can travel only 5 miles to another antenna
that
is only 5' off the water...but can travel 15 miles to an antenna that is
100' high (like at a Coast Guard station).

An 8' antenna mounted on the same gunnel can travel 9 miles to another
antenna that is only 5' off the water (big difference!), but only
travels 18
miles to that 100' antenna (a not so big difference from the 3'
antenna).

If the CG antenna is 250' above sea level (mounted on a tower on a
mountain
for example), the 3' antenna can travel 23 miles...and the 8' travels 25
miles.

So the question is...
Who do you want to call with that radio?

Another boat within 5 miles? Then either antenna is fine.

The Coast Guard when you're 10-15 miles from shore? Then either antenna
is
fine once again.

Here's a good link to explain this further:
http://www.yachtworks.net/Store/antennas.htm

finally - a civilian who gets it.

That's the engineer in me. I like to read how things work before making
my purchases.




Looking at specs is fine. But what happens when the boat, intended for
only near shore use, loses power when at the fringe range of the 3 foot
antenna and there are no boaters anywhere close?

The point I was making is that the 3' antenna will reach a CG tower more
than 15 miles away...and the 8' antenna will reach only about 3 miles
further. That's not really an appreciable difference unless his fishing
grounds are consistently in the 16-18 mile range.

Besides, if he's out in an 18' boat more than 15 miles from shore, he better
be carrying an EPIRB...and filing a float plan. Should he fail to return as
planned, a CG aircraft will pick his radio up from nearly 30 miles or
more...no matter how big his antenna is.

Keep in mind that the antenna on passing ships/shrimp boats/etc. are at
least 30-50' above the water...meaning that his 3' antenna will reach them
almost as well as the 8' antenna.

As I said before, the height of the receiving antenna on most vessels that
are going to render assistance has a greater influence on your radio's
effective range than the height of your own antenna.

I regularly hear CG broadcasts coming out of St. Pete...and I'm 160 miles
from them. Granted, they're using higher power equipment and very tall
broadcast towers (perhaps broadcasting from aircraft), but I hear them on my
boat with the 3' antenna just as well as the Grady with an 8' antenna on top
of the hardtop.