On Mon, 9 Nov 2020 at 18:03, Barry Feierman <k3euibarry@...> wrote:
Here is my next iteration (PDF) of a summary of "Antenna Fundamentals and
Measurements with a Nano VNA".
Comments are appreciated as I am going to be giving a talk with SOME of
these slides at local radio clubs.
TU
Barry k3eui
Philly region
A couple of comments, after a very quick skim read.
1) You say the loss in a coax is due to I^2 R and V^2 / R. However, it's
not the same value of R. You might consider using Rc for the conductor
losses, and Rd for the dielectric losses, where Rd >> Rc. However, these
are not resistors you would measure on a multimeter. Copper losses will
certainly increase with frequency, which I think you cover, and dielectric
losses may too - it depends on the dielectric.
2) You talk about efficiency of an antenna, but don't define it. Most
people don't have a clue what efficiency is. The generally accepted
definition amoung professionals comes from IEEE standard 145. Efficiency is
the power radiated divided by the power absorbed by the antenna. Note the
word absorbed - it has nothing to do with the incident power. So if you
have a crap SWR, you transmit 100 W, 99 W gets reflected, and 0.95 W gets
radiated, then the antenna is 95% efficient, despite you would probably not
consider it a very good antenna.
Dr. David Kirkby, Kirkby Microwave Ltd