On 7/14/2012 11:14 AM, pfizenmayer wrote:
> Which leads me to ask - what is wrong with measuring the attenuation with a
> two port VNA with the choke simply in series between port 1 and port 2 ?(of
> course calibrating out any cables if used) This is basically a "VI"
> measurement and seems to me to give valid measure of the atteuation if the
> Hank K7HP
I have been doing this for over 30 years, and have taught many
others to do it. However, what is "wrong" with the technique
is that network analyzers are only specified in terms of an
insertable coaxial DUT with defined 50 ohm reference planes.
It is up to the user to fixture his actual DUT to look like
this. The fixturing problem is the "final frontier" of
measurement science. The experts don't always agree on what
is the "correct" fixturing modality. Having said that, it
is still plenty useful for ham radio.
A minor issue is that the user has to be able to convert
between the complex variables of S21 and Z. This doesn't
seem to be built in to any NA's that I have seen. Sometimes,
you can do user math and add the capability.
The dual of this technique is useful for very low impedance
DUT's. In this case, you shunt the through line with the DUT.
Watch out for ground loops.
Rick N6RK
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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