Assuming they are both high enough to hit max range, then by definition,
the 6db would put 2x the power in the direction of the receiving station...

Why do bigger boats use 9DB? they stay more horizontal... why sailboats
use 3 DB? They lean to one side for long periods of time.
BUT... VHF is line of site so if you can't "see" the horizon from the
middle of the antenna, you won't be able get the extra distance...

My experience... I have 1 9Db antennas on my sportfish... I can hit 50
miles from Bimini to Fort Lauderdale ONLY when communicating to the big
guys. (USCG, SEATOW, etc)... Why? THey have very tall antennas and I am
concentrating my 25 watts along a very narrow band along the water.

I could never do that with my older 6 DB antennas.



Sailman wrote:
Assuming identical setups and a perfectly vertical antenna, what
percentage increase in range would be likely as a result of changing
from a 3db to 6db VHF antenna?