Up to 800 miles. However, this is very extreme. The phenomena used is atmospheric
ducting, which is common when hot air overrides colder air - very common on the ocean in
the summer.

Also, "line of sight" is a bit misleading, since radio waves (and radar) refract a bit in
the atmosphere, to the horizon is a bit further.

The distance calculation is often given as "1.22 times the sum of the square roots of the
antenna heights." Assuming masts of 49 feet, this lead to a distance of 17 miles.
However, in open water its very common to hear chatter from 25 miles or further. Last
Friday while I was still south of Plymouth, I heard chatter from Salem Bay - maybe 50
miles away.

BTW, there is a theory that very long distance VHF propagation is correlated with
earthquake activity, so if you hear a pickup request from 500 miles away, prepare for a
tsunami!

-jeff


Wally wrote:
Bobsprit wrote:
What is the line of sight distance between the two antennae?

I assume you're aware that VHF signals, while mainly line of sight,
are capable of greater range on occasion.

How much greater range, generally speaking?

Should I switch on my handheld and wait for you to hail me? Channel
9, Bob! I'll be waiting!

No, really, how much greater range?

Assuming masts of 49 feet, this lead to a distance of 17 miles.
However, in open water its very common to hear chatter from 25 miles or
further. Last
Friday while I was still south of Plymouth, I heard chatter from Salem Bay -
maybe 50
miles away.

And there you have it, folks. Wall, I doubt you'll admit you were wrong.
But you are.

RB