[TowerTalk] impedance meter recommendations pse

[Ian White GM3SEK]

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 
>limitations.
>

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.

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.


-- 
73 from Ian GM3SEK