You can also use a Boonton Model 250A RX meter or one of the later models of
the 250A made by HP after they took over Boonton. They appear on eBay
fairly regularly and seem to sell for prices in the $50 to $100 range. They
are not exactly a portable piece of equipment though as they definitely fall
in the boat anchor class of test equipment.
David C. Hallam
KC2JD
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]On
Behalf Of David Kirkby
Sent: Sunday, February 27, 2005 10:48 AM
Cc: amps@contesting.com
Subject: Re: [Amps] close to off topic - how to read antenna R + jX ??
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/
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