Boat Forum / Cruising / September 2005

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.

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

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)

2.4 miles

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.

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.

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