I mentioned earlier the importance of the phase information provided by
the VNA - it not only allows the choke R and X to be identified, but it
also eliminates a measurement error in |Z| inherent at lower values.
If we throw away the phase information, and only measure |S21| with that
test arrangement, we cannot distinguish between the infinite number of
choke impedance values that will produce the same |S21| result. So for
example, any of these choke impedance will produce an identical |S21|
indication:
500 + j0 (|Z| = 500)
400 + j325 (|Z| = 515)
300 + j435 (|Z| = 528)
0 + j570 (|Z| = 570)
We have no way of knowing whether the choke is totally resistive or
totally inductive or something in between; and we only know its
impedance lies somewhere in the range 500 Ohms to 570 Ohms.
Steve G3TXQ
On 03/11/2014 16:44, Steve Hunt wrote:
With the "Generator/Voltmeter" method you can only easily measure
|S21| and therefore the choke Z; but of course the VNA will also give
you the vital S21 phase information and the choke R+jX. Plus, the VNA
carries out the frequency scan automatically and can be calibrated to
take out the effect of the interconnecting leads.
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|