25/d1^2 = 1/d2^2

d1 = 12 so d1^2 = 144

25/144 = 1/d2^2

144/25 = d2^2

d2 = 2.4


"Jim Richardson" wrote in message
...
On Fri, 16 Sep 2005 16:43:10 -0400,
Harry Krause wrote:
With my VHF tranmitting at 25 watts, I can easily reach out from one
side of Chesapeake Bay to the other in most places.

At the 1 watt setting, who knows?

For the sake of discussions, let's say on a clear day from my VHF
antenna, which is approximately 14' above the waterline, a 25 watt
transmission reaches someone 12 miles away with a similar antenna height.

Is there a way to figure how far a 1 watt setting will reach with the
same equipment?




If you assume that conditions are identical (like you are switching
between 1W and 25W settings, rather than on different days), and that
the reciever you are being picked up on, has a sufficient noise floor
and min sig sensetivity, then it's a pretty simple inverse square. There
are some other issues, like very low signal losses in antennas, which
don't scale linearly with power, but as a rough guess, you can probably
reach about 1/8th the distance, under ideal circumstances.


--
Jim Richardson http://www.eskimo.com/~warlock
The laws of physics are not subject to judicial review.

In article ,
Harry Krause wrote:

With my VHF tranmitting at 25 watts, I can easily reach out from one
side of Chesapeake Bay to the other in most places.

At the 1 watt setting, who knows?

For the sake of discussions, let's say on a clear day from my VHF
antenna, which is approximately 14' above the waterline, a 25 watt
transmission reaches someone 12 miles away with a similar antenna height.

Is there a way to figure how far a 1 watt setting will reach with the
same equipment?

It's entirely dependent on the noise on the channel and each boat's
quality of setup. Working with friends on an unusual channel at 1w, we
reliably communicated from HdeG to Georgetown on the Sassafras. They had
a 6db antenna at deck level, ours is 3db 40 feet up. There was some
terrain between us, so we proved that VHF is not strictly line of sight.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

"Jere Lull" wrote in message
...
In article ,
Harry Krause wrote:

With my VHF tranmitting at 25 watts, I can easily reach out from one
side of Chesapeake Bay to the other in most places.

At the 1 watt setting, who knows?

For the sake of discussions, let's say on a clear day from my VHF
antenna, which is approximately 14' above the waterline, a 25 watt
transmission reaches someone 12 miles away with a similar antenna height.

Is there a way to figure how far a 1 watt setting will reach with the
same equipment?

It's entirely dependent on the noise on the channel and each boat's
quality of setup. Working with friends on an unusual channel at 1w, we
reliably communicated from HdeG to Georgetown on the Sassafras. They had
a 6db antenna at deck level, ours is 3db 40 feet up. There was some
terrain between us, so we proved that VHF is not strictly line of sight.

It's been proved many times and has never been considered to be strictly
line of sight.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

With that set up you should get out more than 12 miles???
Capt. Boots
"Doug Dotson" dougdotson@NOSPAMcablespeedNOSPAMcom wrote
in message ...

"Jere Lull" wrote in message
...
In article ,
Harry Krause wrote:

With my VHF tranmitting at 25 watts, I can easily reach
out from one
side of Chesapeake Bay to the other in most places.

At the 1 watt setting, who knows?

For the sake of discussions, let's say on a clear day
from my VHF
antenna, which is approximately 14' above the waterline,
a 25 watt
transmission reaches someone 12 miles away with a similar
antenna height.

Is there a way to figure how far a 1 watt setting will
reach with the
same equipment?

It's entirely dependent on the noise on the channel and
each boat's
quality of setup. Working with friends on an unusual
channel at 1w, we
reliably communicated from HdeG to Georgetown on the
Sassafras. They had
a 6db antenna at deck level, ours is 3db 40 feet up. There
was some
terrain between us, so we proved that VHF is not strictly
line of sight.

It's been proved many times and has never been considered to
be strictly
line of sight.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics)
http://homepage.mac.com/jerelull/BVI/

Why do you have to interject your political views with every post? The
topic of this group should be neutral to politics in most cases. But
for some reason you feel you must make your opinions known to the world
how you feel about President Bush. Please tone it down or take it to
an appropriate group.
-Rob

"Don White" wrote in message
...
Harry Krause wrote:
With my VHF tranmitting at 25 watts, I can easily reach out from one side
of Chesapeake Bay to the other in most places.

At the 1 watt setting, who knows?

For the sake of discussions, let's say on a clear day from my VHF
antenna, which is approximately 14' above the waterline, a 25 watt
transmission reaches someone 12 miles away with a similar antenna height.

Is there a way to figure how far a 1 watt setting will reach with the
same equipment?


Don't know how to calculate that...but in our VHF course we were advised
to use the 1 watt when in a small harbour or at an anchorage. The idea was
that 25 watt was overkill in this situation and would add to the clutter
for people a fair distance away.

That is actually the law.