The difference in four feet (assuming the same gain the the antennae)
you will only be able to communicate 1.18 miles further. Since VHF is
"line of sight" you are limited by the curvature of the earth - the
distance to the horizon.

I went for the 4' fiberglass antenna since I already have enough things
on the boat to stick me in the eye. They are more expensive than
stainless but they also look better in my opinion.


Dan

JR_FXLR wrote:
Greetings to all that are here for boating posts, "bite me" to the rest...

I take delivery of a 2005 Key West 186CC, and I'm waaaay excited. This will
be my first "serious" boat, and I had a question that google isn't making
too clear...

My dealer is installing a 4ft stainless VHF antennae due to my bimini top.
We both agree that an 8ft would get better range, but there isn't a place to
mount it and still use the bimini. My question... can I buy an 8ft, keep it
in one of the side rod holders, and screw it on for emergency calls?

I'd guess that 75 percent of the time I'll be within 10 miles of the harbor
and USCG station, but occasionally I run up the ICW.

Just checking.

JR
05 Key West 186CC (almost)

"Dan Krueger" wrote in message
ink.net...
The difference in four feet (assuming the same gain the the antennae) you
will only be able to communicate 1.18 miles further.

True, or close to it depending on the db gain you used. ;-)

Calculation for Range of an Antenna:

6db Antennas: Square Root of Height (in feet) above water x 1.15= Range in
miles
9db Antennas: Square Root of Height (in feet) above water x 1.52= Range in
miles

So we are talking a range of roughly 3 miles for the 4 foot vs 4.25 miles
for the 8 foot.

Not a big difference as you said.

I assumed the same db gain (but none in particular) since the distance
to the horizon would be the limiting factor. As far as I know, the gain
will only come into play if the antenna is VERY high.

I'm not an expert, I don't play one on TV, and I haven't stayed at a
Holiday Inn Express in over four years.

Dan


JimH wrote:
"Dan Krueger" wrote in message
ink.net...

The difference in four feet (assuming the same gain the the antennae) you
will only be able to communicate 1.18 miles further.


True, or close to it depending on the db gain you used. ;-)

Calculation for Range of an Antenna:

6db Antennas: Square Root of Height (in feet) above water x 1.15= Range in
miles
9db Antennas: Square Root of Height (in feet) above water x 1.52= Range in
miles

So we are talking a range of roughly 3 miles for the 4 foot vs 4.25 miles
for the 8 foot.

Not a big difference as you said.

On Wed, 20 Apr 2005 19:27:22 -0400, "JimH" wrote:


"Dan Krueger" wrote in message
link.net...
The difference in four feet (assuming the same gain the the antennae) you
will only be able to communicate 1.18 miles further.

True, or close to it depending on the db gain you used. ;-)

Calculation for Range of an Antenna:

6db Antennas: Square Root of Height (in feet) above water x 1.15= Range in
miles
9db Antennas: Square Root of Height (in feet) above water x 1.52= Range in
miles

So we are talking a range of roughly 3 miles for the 4 foot vs 4.25 miles
for the 8 foot.

Not a big difference as you said.

You have to remember that the db figure is based on a free space
formula - in short, an imaginary antenna range - it's all math and
perfect performance.

In the real world it's not any where near 6 db for a variety of
reasons including standing waves, ground conditions, radio
performance, height, ground plane, data, data, data. The reason
manufacturer's can advertise the specs is because, in theory, that's
what the antenna will produce given perfect conditions.

Also be careful about the line-of-sight deal. FM also relies on
ground wave much as AM does - it's the reason you can receive an FM
station more than line-of-sight from the FM station antenna.

By the way, there is no such thing as a 9 db antenna unless you are
talking about a Yagi.

Later,

Tom

"Short Wave Sportfishing" wrote in message
...
On Wed, 20 Apr 2005 19:27:22 -0400, "JimH" wrote:


"Dan Krueger" wrote in message
hlink.net...
The difference in four feet (assuming the same gain the the antennae)
you
will only be able to communicate 1.18 miles further.

True, or close to it depending on the db gain you used. ;-)

Calculation for Range of an Antenna:

6db Antennas: Square Root of Height (in feet) above water x 1.15= Range in
miles
9db Antennas: Square Root of Height (in feet) above water x 1.52= Range in
miles

So we are talking a range of roughly 3 miles for the 4 foot vs 4.25 miles
for the 8 foot.

Not a big difference as you said.

You have to remember that the db figure is based on a free space
formula - in short, an imaginary antenna range - it's all math and
perfect performance.

In the real world it's not any where near 6 db for a variety of
reasons including standing waves, ground conditions, radio
performance, height, ground plane, data, data, data. The reason
manufacturer's can advertise the specs is because, in theory, that's
what the antenna will produce given perfect conditions.

Also be careful about the line-of-sight deal. FM also relies on
ground wave much as AM does - it's the reason you can receive an FM
station more than line-of-sight from the FM station antenna.

By the way, there is no such thing as a 9 db antenna unless you are
talking about a Yagi.

Later,

Tom

Yeah, but the point, as Dan brought out, is there is only about a 25%
increase in range when going with an 8 foot antenna of equal ratings and
positioned at the same height (from the waterline) on the boat, which turns
out to be a little more than a mile.

On Wed, 20 Apr 2005 19:58:04 -0400, "JimH" wrote:


"Short Wave Sportfishing" wrote in message
.. .
On Wed, 20 Apr 2005 19:27:22 -0400, "JimH" wrote:


"Dan Krueger" wrote in message
thlink.net...
The difference in four feet (assuming the same gain the the antennae)
you
will only be able to communicate 1.18 miles further.

True, or close to it depending on the db gain you used. ;-)

Calculation for Range of an Antenna:

6db Antennas: Square Root of Height (in feet) above water x 1.15= Range in
miles
9db Antennas: Square Root of Height (in feet) above water x 1.52= Range in
miles

So we are talking a range of roughly 3 miles for the 4 foot vs 4.25 miles
for the 8 foot.

Not a big difference as you said.

You have to remember that the db figure is based on a free space
formula - in short, an imaginary antenna range - it's all math and
perfect performance.

In the real world it's not any where near 6 db for a variety of
reasons including standing waves, ground conditions, radio
performance, height, ground plane, data, data, data. The reason
manufacturer's can advertise the specs is because, in theory, that's
what the antenna will produce given perfect conditions.

Also be careful about the line-of-sight deal. FM also relies on
ground wave much as AM does - it's the reason you can receive an FM
station more than line-of-sight from the FM station antenna.

By the way, there is no such thing as a 9 db antenna unless you are
talking about a Yagi.

Yeah, but the point, as Dan brought out, is there is only about a 25%
increase in range when going with an 8 foot antenna of equal ratings and
positioned at the same height (from the waterline) on the boat, which turns
out to be a little more than a mile.

And my point was that it isn't even that much because of physical
limitations including, but not limited to, antenna height, length and
technical characteristics.

Now, if we want to discuss reception - that is a whole different
story. :)

Later,

Tom

"JimH" wrote in message
...

"Short Wave Sportfishing" wrote in message
...
On Wed, 20 Apr 2005 19:27:22 -0400, "JimH" wrote:


"Dan Krueger" wrote in message
thlink.net...
The difference in four feet (assuming the same gain the the antennae)
you
will only be able to communicate 1.18 miles further.

True, or close to it depending on the db gain you used. ;-)

Calculation for Range of an Antenna:

6db Antennas: Square Root of Height (in feet) above water x 1.15= Range
in
miles
9db Antennas: Square Root of Height (in feet) above water x 1.52= Range
in
miles

So we are talking a range of roughly 3 miles for the 4 foot vs 4.25 miles
for the 8 foot.

Not a big difference as you said.

You have to remember that the db figure is based on a free space
formula - in short, an imaginary antenna range - it's all math and
perfect performance.

In the real world it's not any where near 6 db for a variety of
reasons including standing waves, ground conditions, radio
performance, height, ground plane, data, data, data. The reason
manufacturer's can advertise the specs is because, in theory, that's
what the antenna will produce given perfect conditions.

Also be careful about the line-of-sight deal. FM also relies on
ground wave much as AM does - it's the reason you can receive an FM
station more than line-of-sight from the FM station antenna.

By the way, there is no such thing as a 9 db antenna unless you are
talking about a Yagi.

Later,

Tom

Yeah, but the point, as Dan brought out, is there is only about a 25%
increase in range when going with an 8 foot antenna of equal ratings and
positioned at the same height (from the waterline) on the boat, which
turns out to be a little more than a mile.


Actually double the distance, as the other person probably has an 8'
antenna.