On Sep 25, 10:51 am, Larry wrote:
John H. wrote :

Anyone - Is the performance of the 5' antenna seriously below that of the
8'er?

None whatsoever. I got to the horizon on a Metz Manta 6 halfwave at butt
level in a Sea Rayder jetboat all the time.

VHF only goes to the horizon, line of sight. To get further, you must
extend the horizon with ALTITUDE. 5' to 8' means nothing.

Screw a bunch of sun-destroyed fiberglass rods. The Metz is guaranteed for
life unless you lose the whip out of it. All the USCGs boats use the Metz,
a testimonial to its rugged construction. Completely self-contained. No
ground plane required. It'll work the horizon holding it in your hand.http://www.metzcommunication.com/manta6.htm
Great company, too.

This guy has it on sale:http://www.northeastmarineelectronics.com/index.asp?
PageAction=VIEWPROD&ProdID=2984
$34! That's half price!

Larry
--
Search youtube for "Depleted Uranium"
The ultimate dirty bomb......

If distance goes as square root of the height, a 3' antenna mounted on
the same mount as the 8' antenna will reduce my distance by only about
40%.

I may be wrong about this but I think the shorter antennaes are less
"gain". This means they send less power in a horizontal plane.
Sailboats use low gain antennaes because they heel but generally have
them up very high.

Bottom line, I suspect the real answer is that the 3' antenna probably
loses more than 50% of the range due to "gain" and distance to
horizon.

My options (with bimini):

1. Mount the 8' antenna on the side "gunnel" where it would interfere
with casting AND be about 2' lower, effectively being the same as a 6'
antenna (except for gain) AND requiring more coax.
2. Mount the 8' antenna on the heavy stainless bimini tube support
getting back 1' of height.
3. Replace the 8' antenna with a 3' antenna but carry the 8' one for
use in an emergency.

On Tue, 25 Sep 2007 09:59:02 -0400, "Eisboch"
wrote:


"Reginald P. Smithers III" wrote in message
...

VHF transmission range is a function of transmitter power, receiver
sensitivity, and distance to the horizon, since VHF signals propagate
under normal conditions as a line-of-sight phenomenon.

The way to calculate the the theoretical line-of-sight horizon distance
is:
distance in miles = The square root of (1.5 X the height of the antenna
from the water in feet)

It's also a function of the proper matching of antenna length, usually
expressed in quarter wavelength values, for the lowest SWR value which
yields maximum power transfer of the radio's power. The shorter the
antenna, the more difficult it is to match it to the transmitting frequency.
Many short antennas have additional windings of wire to make the antenna
appear "longer" in order to get lower SWR readings and protect the radio's
output stages, but don't help with maximizing the effective radiated power.

Very few people adjust the antenna length to get maximum range. In many
cases the 25 watts you think you are transmitting with is in reality much
lower and can vary widely installation to installation.

Yep.

On Tue, 25 Sep 2007 07:01:13 -0500, John H. penned the following well
considered thoughts to the readers of rec.boats:

With the new Key West, I'm getting a bimini. The wife didn't think the
t-top would give enough sun protection.

In one of the shots of your boat, Harry, it appeared that you have the 8'
antenna folded down, although it could have been a 5'er I guess. In any
case, what do you have, and does it interfere with the bimini?

Anyone - Is the performance of the 5' antenna seriously below that of the
8'er?

By formula, 3' vs. 8' is about 2.74 miles difference in LoS..... which
is fairly meaningless..... since we don't know the altitude of the
other antenna. For safety, I rely on the height of the local 170+ foot
USCG antenna, instead of the height of my own......

Receiver sensitivity is probably way more important than +-5' of
antenna at the boat end.... unless you are trying to DSC some guy near
the horizon....

...... sooooo.....
save that money on the antenna and spend it on the IC-M604...

--

Grady-White Gulfstream, out of Oak Island, NC.

Homepage
http://pamandgene.idleplay.net/

Rec.boats at Lee Yeaton's Bayguide
http://www.thebayguide.com/rec.boats
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On Tue, 25 Sep 2007 08:32:14 -0700, Frogwatch
wrote:


If distance goes as square root of the height, a 3' antenna mounted on
the same mount as the 8' antenna will reduce my distance by only about
40%.

I may be wrong about this but I think the shorter antennaes are less
"gain". This means they send less power in a horizontal plane.
Sailboats use low gain antennaes because they heel but generally have
them up very high.

Hmmm - it's a bit more complicated that that.

The long/short of it is that antenna gain is based on the hallowed
theoritical half-wave dipole in free space - eerything is compared to
that.

It really doesn't matter if it's horizontal or vertical.

Bottom line, I suspect the real answer is that the 3' antenna probably
loses more than 50% of the range due to "gain" and distance to
horizon.

Not really. Of course it depends on the rating of the antenna in
terms of power, but a 3' antenna should be as capable of handling 25
watts as an 8' antenna.

Gain is a tricky term to use. The antenna, at it's designed frequency
will provide "gain" of X dB over space at a 1:1 SWR (Standing Wave
Ratio). So if you have 9 dB of "gain" at 1:1 that doesn't mean that
you have tripled your Effective Radiated Power - more like you have
increased the ERP by 40% or thereabouts for reasons beyond the point
of this discussion.

Where the loss comes in is away from the center frequency as the SWR
rises. At 1:1 you are getting the power efficiently transmitted. The
further you move up and/or down the frequency range, the SWR rises
which introduces loss. That loss, in dB, is subtracted from the
"gain" resulting in decreased ERP.

There are also other factors to consider such as ground system,
height, type of antenna, ability to retune, etc.

Properly installed, there is no honest advantage to a 8' antenna over
a 3' antenna for small boats.

For larger boats, that's a whole different ball of wax. :)

On Tue, 25 Sep 2007 11:50:39 -0400, Gene Kearns
wrote:

By formula, 3' vs. 8' is about 2.74 miles difference in LoS..... which
is fairly meaningless..... since we don't know the altitude of the
other antenna. For safety, I rely on the height of the local 170+ foot
USCG antenna, instead of the height of my own......

Agreed.

..... sooooo.....
save that money on the antenna and spend it on the IC-M604...

Agreed. :)

On Tue, 25 Sep 2007 16:04:59 GMT, Short Wave Sportfishing
wrote:

Agreed. :)

You're awfully agreeable today. What's up?

Eisboch wrote:
"Frogwatch" wrote in message
oups.com...
Proof that this NG does some good for boaters and is not all
politics. I face the same issue in that I have an 8' antenna on my
Tolman but recently installed a bimini and have not been sure of what
to do about the antenna. Harry says his 3' antenna works fine and
clears the bimini............


I installed a 3' antenna and Icom radio on the console of a Dauntless Whaler
I had. No bimini, but I didn't want a long antenna in the way while fishing
and the short, stainless whip could be bent over under the console grab
rail, out of the way.

It worked, but didn't have nearly the range of an 8 footer mounted higher up
on a boat. As for 10 mile range? No way on mine. Maybe two at best.

Eisboch




Mine is mounted on a vertical rail on the side of my center console.
When up, it just clears the underneath of the bimini, and the bimini
clears the top of my head by at least six to eight inches, so I am
guessing the tip of the antenna is somewhere close to 7' off the deck of
the boat. It seems to work well for me, although I rarely use VHF, since
almost everyone is on cell, even the guys I chat with who are fishing on
their boats out on the bay.

John H. wrote:
On Tue, 25 Sep 2007 08:00:11 -0400, HK wrote:

HK wrote:
John H. wrote:
With the new Key West, I'm getting a bimini. The wife didn't think the
t-top would give enough sun protection.

In one of the shots of your boat, Harry, it appeared that you have the 8'
antenna folded down, although it could have been a 5'er I guess. In any
case, what do you have, and does it interfere with the bimini?

Anyone - Is the performance of the 5' antenna seriously below that of the
8'er?

I haven't noticed any difference on the Bay with my five-footer. (I was
going to go with an eight-footer, but decided I wanted one that would
fit under the bimini). Only used it a couple of times, but "raised"
other boats maybe 10 miles away, and of course, no problems hearing or
raising the CG with its high land towers.

Whoops...my antenna is a 3' unit, not a five-foot unit. It was
positioned to just clear the bimini. Works fine. I lower it when I put
the cover on the boat.

The three footer sounds even better. Post a pic when you get a chance.


Whoops. Could have done that this am, since I just towed the boat back
from Cobb Island. Saw a Key West dealer near there, stopped in to see
what all the fuss was about. This is the dealer in Maryland on Route 301
about two miles north of the Potomac River bridge.

Gene Kearns wrote:
On Tue, 25 Sep 2007 07:01:13 -0500, John H. penned the following well
considered thoughts to the readers of rec.boats:

With the new Key West, I'm getting a bimini. The wife didn't think the
t-top would give enough sun protection.

In one of the shots of your boat, Harry, it appeared that you have the 8'
antenna folded down, although it could have been a 5'er I guess. In any
case, what do you have, and does it interfere with the bimini?

Anyone - Is the performance of the 5' antenna seriously below that of the
8'er?

By formula, 3' vs. 8' is about 2.74 miles difference in LoS..... which
is fairly meaningless..... since we don't know the altitude of the
other antenna. For safety, I rely on the height of the local 170+ foot
USCG antenna, instead of the height of my own......

Receiver sensitivity is probably way more important than +-5' of
antenna at the boat end.... unless you are trying to DSC some guy near
the horizon....

..... sooooo.....
save that money on the antenna and spend it on the IC-M604...



I went with the IC-M504. Enough is enough, especially for a radio I will
rarely use, since it isn't nearly as effective to chat with other
fishing guys as a cell phone.

Short Wave Sportfishing wrote:
On Tue, 25 Sep 2007 08:32:14 -0700, Frogwatch
wrote:


If distance goes as square root of the height, a 3' antenna mounted on
the same mount as the 8' antenna will reduce my distance by only about
40%.

I may be wrong about this but I think the shorter antennaes are less
"gain". This means they send less power in a horizontal plane.
Sailboats use low gain antennaes because they heel but generally have
them up very high.

Hmmm - it's a bit more complicated that that.

The long/short of it is that antenna gain is based on the hallowed
theoritical half-wave dipole in free space - eerything is compared to
that.

It really doesn't matter if it's horizontal or vertical.

Bottom line, I suspect the real answer is that the 3' antenna probably
loses more than 50% of the range due to "gain" and distance to
horizon.

Not really. Of course it depends on the rating of the antenna in
terms of power, but a 3' antenna should be as capable of handling 25
watts as an 8' antenna.

Gain is a tricky term to use. The antenna, at it's designed frequency
will provide "gain" of X dB over space at a 1:1 SWR (Standing Wave
Ratio). So if you have 9 dB of "gain" at 1:1 that doesn't mean that
you have tripled your Effective Radiated Power - more like you have
increased the ERP by 40% or thereabouts for reasons beyond the point
of this discussion.

Where the loss comes in is away from the center frequency as the SWR
rises. At 1:1 you are getting the power efficiently transmitted. The
further you move up and/or down the frequency range, the SWR rises
which introduces loss. That loss, in dB, is subtracted from the
"gain" resulting in decreased ERP.

There are also other factors to consider such as ground system,
height, type of antenna, ability to retune, etc.

Properly installed, there is no honest advantage to a 8' antenna over
a 3' antenna for small boats.

For larger boats, that's a whole different ball of wax. :)


Thank goodness the alternator on my trusty Yamaha puts out 20 GJ of
juice for my VHF radio and towed array barge.