This six mile radio says in the FCC specs that it puts out only less than
half a watt...am I reading that right?

Most of the 2 billion cell phones that are in existence in the whole world
(yes, 2 billion! US, China, Russia, even 100 million in India, plus
everywhere else) put out less than one watt. And, I see cellphone towers
spaced, what, ten miles +/- appart all over where I live and most cell
phone calls are not over strict line-of-sight paths. Might not be a
totally fair comparison, but some food for thought.

Yup. Raw transmit power isn't the only factor. The tower height is
an essential element of this system.

An interesting web page to read can be found at

http://www.firestik.com/Tech_Docs/dist2horizon.htm

It discusses the distance to the visual horizon, as well as the "radio
horizon" distance based on the antenna height (radio waves can often
travel some distance beyond the visual horizon, for a variety of
reasons).

According to the formula in this page, two radios whose antennas are
located 6' above the ground, will have a radio-horizon distance of a
bit less than 7 miles. At any distance greater than that, the Earth's
surface will block the direct path between the two radios, and
reliable communication (on FRS/GMRS and other UHF frequencies at
least) will probably be difficult or impossible. Add in the effect of
ground clutter (buildings and trees blocking the direct path and
generating reflections) and you end up with a much shorter useful
range.

Raising one radio up onto a building or hill greatly increases the
transmission distance, for at least two reasons - it gets one radio
out of the ground clutter and it increases the radio-horizon
distance. With one radio at 100' and the other at 6', the radio
horizon distance extends out to more than 17 miles.

The horizon distance and the presence of ground clutter often make
more of a practical difference than raw transmit-power level. Going
from 500 milliwatts to 5 watts is a 10:1 increase, which works out to
a clear-line-of-sight range increase of around 3:1 - but if the other
guy is over the radio horizon, you may not actually get any better
communication using the higher power.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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