Bruce in alaska wrote:
In article ,
"Marcus Tait" wrote:


Hi,
I have just been tuning a 400MHz 1/4 wave antenna (approx 170mm length of
wire). I connect a receive antenna to a spectum analyser and the antenna to
be tuned to the signal generators 50ohm output. I set the signal generator
to 400MHz and adjusted the length of the antenna to get a maximum peak on
the spectrum analyser. My question is when i have tuned the antenna for
maximum output at 400MHz is the antenna then tuned to 400MHz or is the
antenna's impeadance tuned to 50ohm or both?


The way the "Big Boys" do this is with an Impedance Bridge connected
to the Spectrum Analyzer, Tracking Generator, Antenna, and 50 Ohm
Termination Load.

Or with their handy dandy Vector Network Analyzer, which essentially
rolls all of the above stuff into one convenient package. There's a
fair number of mfrs selling VNAs targeted to this kind of market (i.e.
standing out in the wind on a tower, as opposed to in a nice quiet
anechoic chamber indoors). There's some nice stuff for antenna ranges
too (fiber optic connections to the remote measurement point, for instance).