At 01:53 PM 12/28/2006, Ian White GM3SEK wrote:
>Jim Lux wrote:
> >At 08:24 AM 12/28/2006, Richard \(Rick\) Karlquist wrote:
> >>Anyone interested in this topic should read the
> >>recent QST article on the AIM-4170 antenna analyzer.
> >>The article has a shoot out of this unit vs other
> >>ham units and even an Agilent NA. It is a true
> >>vector analyzer with a narrowband receiver. Most
> >>other analyzers are scalar analyzers that use
> >>the "3 voltmeter method" to determine phase angle
> >>(which is why they can't determine sign) and use
> >>a broadband detector, which is susceptable to BC
> >>interference. The N2PK design is similar, but you
> >>have to homebrew it, AFAIK.
> >Actually, the 3 meter method can determine phase, except you need one
> >more volt meters. That's really the basis of the 6 port network
> >approach (6 ports: 1 input, 1 output, 4 measurement ports)
> >However, as Rick points out, broadband detectors have their
>For the record (and correcting an error in the 4th edition of ON4UN's
>'Low Band DXing') the N2PK VNA does not have a broadband detector, and
>does not suffer from those well-known limitations.
I should clarify.. my comment about broadband detectors is just for
various and sundry bridge/3 meter/6 port network schemes.
And, for what it's worth, one could always use a tuned detector with
any of those schemes.
>It uses a narrowband measurement method that continues to give accurate
>antenna impedance readings in the presence of strong off-frequency
>signals. If the interfering signal is stronger than the threshold of
>detector burnout (above 10mW), the VNA can be physically protected by a
>band-reject filter without any significant loss of measurement accuracy.
I presume one would redo the cal with the filter in place?
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