Measure the difference of length by VNA, is it necessary to calibrate?

[votientu]

Mesure the difference of length by VNA, is it necessary to calibrate ?

I have a question concerning the necessity of calibration in my measurement by VNA.
In fact, the measurement time is very important in my setup, so I would like to ask if the calibration correction is necessary ?

Here is my measurement (it is just an example):

It is to measure the length of a cable (50 Ohm), I don't know the length of this cable,

I have a cable (50 Ohm) with a reference length of 1 m. I will measure S21 by VNA in 2 cables. From the phase of S21 I will know the length of these two cables, maybe the lengths are wrong because I did not calibrate the VNA before. But is the difference of length I calculate from the difference of phase S21 give me the good result ?

Let's suppose the the cable in question is with length from 0.9-1.1 m, so the difference of phase gives the difference of length.

Thanks !

 

[Romansh]

Re: Mesure the difference of length by VNA, is it necessary to calibrate ?

I don't see any problem with this kind of differential test. Just use frequency high enough to get required measurement resolution.

 

[biff44]

Re: Mesure the difference of length by VNA, is it necessary to calibrate ?

calibration becomes more important the junkier your VNA is. If it is not a good 50 ohm source....and your cables have poor return loss....a proper calibration can cure some of that.