On Tue, 22 Jun 2004 16:42:17 +0300, AP wrote:

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?

3db, etc. stands for 3 decibels gain. 3 decibel gain is twice the gain.
The next question is usually "gain over what"? More properly, 3 db usually
refers to gain over a 1/2 wave dipole. If specified as "dbi" then it means
decibel gain over isotropic which is a point source.

No, all vhf antennae are not the same, but I wouldn't put too much
confidence in advertised gain. That said, the higher the number, the
greater the gain. That usually translates in greater vertical height in
the case of vhf antennae.

How does it obtain the gain? Consider that an isotropic antenna radiates
power equally in all directions. Certainly, any power radiated straight up
or straight down is wasted - there is nobody there to receive it. Antennae
get their gain by concentrating their power in the horizontal plane. The
radiation pattern resembles a doughnut. The greater the horizontal
"squeeze", the greater the gain. This is done by stacking elements and
using phase to concentrate power horizontally.

db stands for "decibels" Decibels are a logarithmic measure.
--

Larry W1HJF
email is rapp at lmr dot com