Nope -- you can not get out more power than you put in.
Antenna gain is essentially squishing energy into a narrower pattern.
Hence gain over the previous pattern or reference antenna in a given
direction and angle
Gain is referenced to a dipole or isotropic radiator

antenna gain: The ratio of the power required at the input of a loss-free
reference antenna to the power supplied to the input of the given antenna to
produce, in a given direction, the same field strength at the same distance.
Note 1: Antenna gain is usually expressed in dB. Note 2: Unless otherwise
specified, the gain refers to the direction of maximum radiation. The gain
may be considered for a specified polarization. Depending on the choice of
the reference antenna, a distinction is made between:


a.. absolute or isotropic gain (Gi), when the reference antenna is an
isotropic antenna isolated in space;

b.. gain relative to a half-wave dipole (Gd) when the reference antenna is
a half-wave dipole isolated in space and with an equatorial plane that
contains the given direction;
For example: A radio's transmitting power can be concentrated along the
horizon by use of a GAIN antenna. Although you may still be transmitting
with four watts of power, your EFFECTIVE RADIATED POWER (ERP) will be
greatly increased.
See URL: http://www.firestik.com/Tech_Docs/gain_erp.htm

Some more references
http://www.arrl.org/members-only/tis...df/8211035.pdf

http://www.marcspages.co.uk/tech/antgain.htm


--
73 From Key Largo
--------------------------
"Liam Ness" wrote in message
news
I've been homebrewing some simple part 15 transmitters and have always
thought that I was safely within part 15 by controling the RF output.
I use a spice program to estimate my output levels. I just read a web
page that suggests a antenna can increase the RF output power and I
wanted advice if that is true. It was suggested that output could be
increased from 30milliwatts to 60milliwatts by using this antenna. I
understand how you could increase voltage with a decrease in amperage
and vice versa, but I was under the assumption that you couldn't
increase total power without adding more power. I thought it would
violate one of the laws of thermodymanics otherwise. They didn't seem
to be talking about more effieciently radiating the transmitters
power, but actually increasing it above what is present at the antenna
port.

Could someone confirm whether it is posible to increase the power
output of an RF transmitter above the total presented to the antenna.
If it is, I'd appreciate any pointers to information about this. I
don't want put myself out of part 15 by a poor antenna choice. (even
though I still can't believe that it is possible, it sounds to much
like perpetual motion)

TIA