[GeoStL] Re: Product: GMRS - 10Mile; 3Watt; 'Think Speak'
- From: "J.A. Terranson" <measl@xxxxxxx>
- To: geocaching@xxxxxxxxxxxxx
- Date: Sun, 5 Jun 2005 12:00:53 -0500 (CDT)
-
On Sun, 5 Jun 2005, Glenn wrote:
> At 10:55 AM 6/5/2005, Glenn wrote:
> >10 miles mite be quite possible. Most of the GMRS raidos that we all
> >use are 1 watt max. transmit power. The T7100's are 2 watt and the
> >Midlands that Kono is looking at
> ><http://www.dak.com/reviews/2027story.cfm?Ggmrs#pic>http://www.dak.com/reviews/2027story.cfm?Ggmrs#pic
> >are 3 watt.
> >
> >The 2 extra watts would be a nice boost.
> >At 10:14 AM 6/5/2005, Chris Binder wrote:
> >
> >>I have some motorola T7100's. They advertised a 7 mile range on
> >>them. They are absolutely true. I can talk from my house, near
> >>Barnes-Jewish St. Peters Hospital, and talk to my friend who lives
> >>near south high. 6 miles as the crow flies, and I'm fairly sure I
> >>can get that 7th mile out of them because I can still hear clearly
> >>after 6 miles.
There are two things to remember about portable radios: (1) Wattage does
not have a linear relationship to distance, and (2) the more power you
push the shorter your battery life is. The trick is to balance these two
problems.
As someone who has been using commercial band portables for over 30 years,
I have come to adore the radios that allow you to switch power outputs at
will - normally, I stay at .5 or 1 watt, depending on what I expect to be
doing. If that doesn't cut it, I can then move up to the full rating of
the radio in use (usually 5 watts). This maximizes battery life.
As to distance, a 4 watt radio does not "reach" twice as far as a 2 watt
radio. While I forget what the actual formula is, in practice I'd say you
can generally expect about a 1.5x increase in distance for every 2x
increase in power. At the same time you cut battery life in half for
every doubling in power.
Of coursem the above numbers all assume that a 1 watt radio actually puts
out 1 watt, and thereby conveniently ignores something called Effective
Radiated Power ("ERP"). ERP is what you really care about, and it's most
affected by the antenna choice. A 1 watt radio with a really crappy
"rubber duckie" antenna may have an ERP of .3 watts, while the same radio
with a really good center loaded whip could reach an ERP of 1.8!
The moral of the story is to buy the radio you can afford, but buy the
best antenna you can find.
--
Yours,
J.A. Terranson
sysadmin@xxxxxxx
0xBD4A95BF
"Never belong to any party, always oppose privileged classes and public
plunderers, never lack sympathy with the poor, always remain devoted to
the public welfare, never be satisfied with merely printing news, always
be drastically independent, never be afraid to attack wrong, whether by
predatory plutocracy or predatory poverty."
Joseph Pulitzer
1907 Speech
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