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?