[Amps] close to off topic - how to read antenna R + jX ??

David Kirkby david.kirkby at onetel.net
Sun Feb 27 10:47:33 EST 2005


If anyone is serious about making antenna impedance measurements you 
might want to consider getting a used HP vector voltmeter (make sure it 
has the probes). With a coupler, and some attention to calibration 
(short and open circuit loads), you should be able to make reasonably 
accurate measurments, even without the expense of getting it 
professionally calibrated. I used one on the final year project of my 
first degree, looking at a vertical antenna with stacked quarter and 
half wave sections. I measured R+jZ, then used a section of transmission 
line of the right impedance to convert this to 50 + j0.

Looking on eBay, an HP vector voltmeter can be bought for the same sort 
of prices of these amateurish instruments.

Read up about them before shelling out $$'s, but I think for real 
measurments, you would hard to beat for the money. They are not battery 
powered, so not much use up an antenna, but there is no reason you can 
not make the reference plane the end of a bit of coax.

A vector network analyser would be better, but then, even used, these 
are serious money.

-- 
Dr. David Kirkby, 
G8WRB

Please check out http://www.g8wrb.org/ 
of if you live in Essex http://www.southminster-branch-line.org.uk/





More information about the Amps mailing list