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?

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?

So how should I think about translating "2x the power" into a rough
estimate of increased distance?

Ed wrote in message . ..
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?

In article ,
(Sailman) wrote:

So how should I think about translating "2x the power" into a rough
estimate of increased distance?

You really can't. Once you hit the Radio Horizon for your antenna
height, any increase in power is just going out over the heads of your
intended listeners. By increasing the power, you will cause your signal
to noise ratio to improve at the Radio Horizon, but you really don't
extend that horizon by increasing the power, or the antenna gain.
The exceptions to the preceeding rule are, that Vhf Signals can, and do,
DUCT in Thermal Inversion Layers, that are common in some places. These
ducts can cause Vhf signals to be heard and communicated on, many
hudreds of miles further than the Radio Horizon. They do, however,
change and disappear quite often, with weather fronts, and shouldn't be
reallied on for communications.

I pioneered a bunch of these Vhf/Uhf Paths in Brystol Bay, Alaska,
for the Salmon Industry, back in the late 70's, that are still in
use today. When a Low Pressure Front moves thru the area, these Radio
Paths go Stoned Dead for a few days untill the thermal Inversion
rebuilds. Path Studies that we did back then, showed that these things
were good for 60 to 70 days out of the 90 day Salmon Season, and that
justifdied using them, untill good phone service was established in the
region. Now they are just a cheap backup for commercial communications.


Bruce in alaska Who gives Bill Forgey, K7KDU all the credit for
coming up with the idea, in the first place....
--
add a 2 before @

"Bruce in Alaska" wrote

Paths go Stoned Dead for a few days untill the thermal Inversion
rebuilds. Path Studies that we did back then, showed that these things
were good for 60 to 70 days out of the 90 day Salmon Season, and that
justifdied using them, untill good phone service was established in the
region. Now they are just a cheap backup for commercial communications.

In really warm waters, the tropo-ducting is an annoyance that brings
unwanted radio traffic from hundreds of miles away, and it does this most
nights in the summertime.

http://www.iprimus.ca/~hepburnw/tropo_xxx.html

Find your ocean and see what the ducting forecast is.

Jack

In really warm waters, the tropo-ducting is an annoyance that brings
unwanted radio traffic from hundreds of miles away, and it does this most
nights in the summertime.

Here in southern SC, at times we can hear Ft Mason, NC CG down to Ft
Lauderdale and Miami to give those that have never experienced it an idea.

Leanne
s/v Fundy

A small (and often confused) point - a 6 dB increase is 4x the power - not
2x. The formulas a
dB = 10 log10 (P1/Pref)
= 20 log10(V1/Vref)
where P1, Pref are power levels, V1, Vref are voltage (or current, or field
strength) levels. If P1/Pref = 2 , then dB = 3. It all comes about
because P = (V^2)/R.
Derek

"Ed" wrote in message
...
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?

True, a 6db gain is four times the power. But the question was comparing a
3db gain antenna to a 6db gain antenna. The difference is 3db, or two times
the effective radiated power.

Don't forget, RTFQ.

Rusty O

In article fJdEc.125914$eu.79506@attbi_s02,
"Derek Rowell" wrote:

A small (and often confused) point - a 6 dB increase is 4x the power - not
2x. The formulas a
dB = 10 log10 (P1/Pref)
= 20 log10(V1/Vref)
where P1, Pref are power levels, V1, Vref are voltage (or current, or field
strength) levels. If P1/Pref = 2 , then dB = 3. It all comes about
because P = (V^2)/R.
Derek

Your are correct in your math, but 4x Power is illusionary when trying
to compare the range difference between the two signals. 4x Power
doesn't get you anything, but better signal to noise at the Radio
Horizon, which is what the original poster asked.......

me

What is this 3db,6db,9db etc.
Are the VHF antennas all the same? (excluding heght).
What db stands for??
Pls give me an idea.
tks
AP

"Sailman" wrote in message
om...
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?