Liam,

You are absolutely right that the antenna cannot radiate more power
than you feed it. They are probably talking about "effective ratiated
power", which is closely related to antenna gain. You get more power
at the receivers, but only in the directions where radiation is
maximized. For example, a Yagi directs the power more in one
direction, and a "vertical collinear" directs it in a horizontal
plane. Each does so at the "expense" of power radiated in other
directions, but if you don't care about reaching receivers in those
other directions, it's not a problem. But be careful: do the rules
limit the maximum power, or the maximum ERP (effective radiated
power)? (The same thing works for receiving, too. You can use
antenna directivity to increase the received signal level, and to
reject signals or noise coming from directions you don't care about
receiving.)

Cheers,
Tom

Liam Ness wrote in message . ..
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