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

[David Kirkby]

David C. Hallam wrote:

>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
>
I've not used the Boonton 250A, and would suggest anyone looking at 
buying any of these professional instruments did a bit of research 
first. Perhaps buy a manual before the kit - you can always sell the 
manual if you find the kit it not suitable.

You really need to be *serious* about wanting the decent impedance 
(R+jX) measurements, and able to do the maths, but if you are, then I 
personally think some money spent on old used professional test 
equipment might be better value than spending the same money on brand 
new glossy kit from the likes of MJF. I've not used any of their antenna 
analsers, but having seen some of their kit, I'm not too impressed.

Others might disagree of course.  Is there anyone using such 
professional kit for ham radio use on here, who might like to comment?

My BSc project report would be useful here, but it was written using the 
old word processor 'runoff' on a VAX running VMS. I don't have the 
runoff file, which is a shame, as I'm sure converting a runoff file to 
pdf would not be too hard. I can't be bothered to scan it.

Dr. David Kirkby, G8WRB.


>-----Original Message-----
>From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]On
>Behalf Of David Kirkby
>Sent: Sunday, February 27, 2005 10:48 AM
>Cc: amps at 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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-- 
Dr. David Kirkby, 
G8WRB

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