Reaching out with one watt of VHF
 

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.

Don White wrote:

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.

Crap clutter Don where in the Harbor, as many wats as you want. Harry
your 1 watt is good for boats that are around you and probably not much
more, the 25 will almost get you to Washington and the Bush minions.

Assuming the simplest model (probably wrong), the antenna height
shouldnt matter cuz VHF is s'posed to be line of sight but assume it
is. So you use 1/r^2 and get that 1 watt should reach 1/5 as far as 25
watts. This is prob close enough but I bet there's some refraction and
bending of the pattern 'n such along the earths curve that might depend
on total power (I am not sure how it would depend on power though).

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?

No.

The problems are ERP (effective radiated power), environmental
conditions and physical conditions. ERP is based on power to the
antenna and then its actual dB gain. So, if you have a 1W transmitter
with no antenna attached, your ERP is probably going to be near zero.
Put on a duck stick and you might get +3DbM. Get a long duck and it
might be +6DbM. Energy falls off with the square of the distance. So
doubling the power won't get you twice as far. All other things being
constant.

Environmental conditions can mess up all communications below 350MHz.
Yes, it can mess up those above but higher frequencies are more line
of sight. HF is dependent on the ionisphere for reflectance around
the diameter of the Earth. VHF does not do this very well. UHF
doesn't either.

You might easily get four NM on one day and 2 NM on another.

Overall, it good that the makers include different power settings.

N6OIJ

Gary Gaugler, Ph.D.
Microtechnics, Inc.
Granite Bay, CA 95746
916.791.8191
gary@microtechnics dot com

He did IMPLY that all conditions were equal in the case of 1 watt and
the case of 25 watts. Given that, all thats left is the old 1/r^2
which means that 1 watt gives 1/5 the distance of 25 watts.

Harry Krause wrote in
:

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


Sometimes 1 watt will get you 10 miles. It depends a LOT on the condition
of your antenna system and the other guy's corroded up old piece of crap
with the rotten coax, seized connectors, all full of rain/seawater in the
bilge hooked up, eventually after those 3 kinks where he screwed the
wallboard in too hard, to that corroded up old Standard he moved over from
his center console fishing boat.

Because his radio system hasn't been properly maintained or tested in
years, and he's too naive to know any better or care, better leave it on 25
watts and hope he hears you through the noise of his buzzing inverter and
those loose, corroded connections in the 12V breaker panel that never got
cleaned, either.

Assume the worst, run the power, then after you've gotten him to respond,
switch power levels to 1W and see if he still responds or starts telling
you you're noisy. Of course, this all assumes he can hear you over
Smiley's Marina and Raw Bar running 25 watts from Smiley's 70' tower over
the office talking to the boat on his gas dock that's so close he can read
the date on the DNR license tag, jamming boat radios for 40 miles in all
directions....(sigh)

--
Larry

2.4 miles

"Harry Krause" wrote in message
...
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?





--
- - -
George W. Bush, our hero!

George W. Bush is a Category 5 National Disaster.

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.

On 16 Sep 2005 18:12:59 -0700,
wrote:
He did IMPLY that all conditions were equal in the case of 1 watt and
the case of 25 watts. Given that, all thats left is the old 1/r^2
which means that 1 watt gives 1/5 the distance of 25 watts.



There are some other practical considerations, mostly minimum
sensitivity of the receiver, and it's noise floor, and power losses in
antennas, which vary non-linearly with power.


--
Jim Richardson http://www.eskimo.com/~warlock
Chaos, panic, & disorder - my work here is done

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.