Microwave VSWR Measurement on Oscilloscope

I am using the microwave testbench shown in figure for Standing Wave Ratio measurement.
I have two choices:
one using VSWR Meter,other using CRO.
Can I apply the direct formula (SWR=maximum voltage/minimum voltage) to the square wave
displayed on CRO ?

But according to lab manual (SWR=Square root of maximum voltage/Square root of minimum

voltage). Why we are taking the square root ?


[img=http://s3.postimage.org/1bl5dl9xg/vswr.jpg]

Taken the square root you will get a voltage that is proportional to the RMS voltage of the waveform.

You can use VSWR = (max measured voltage) / (min measured voltage) = (incident wave amplitude + reflected wave amplitude) / (incident wave amplitude - reflected wave amplitude)

pancho_hideboo said:

What do you mean by "CRO" ?.

Click to expand...

Pancho you must be very very young CRO = Cathode Ray Oscilloscope a very old term, much older than me and I feel ancient

Dave

davenn said:

Pancho you must be very very young

Click to expand...

I'm relative old.

davenn said:

CRO = Cathode Ray Oscilloscope

Click to expand...

Thanks for teaching.

However why is CRO located in such place ?
Where is DUT ?

A Place where Detector Mount(XD-451) is located should be a place where DUT is located.

Even if places of Detector Mount(XD-451) and CRO are proper, what signal should we use as horizontal sweep signal for CRO ?

vinodquilon said:

But according to lab manual (SWR=Square root of maximum voltage/Square root of minimum voltage).
Why we are taking the square root ?

Click to expand...

It is because VSWR meter uses square-detector.

vinodquilon said:

Can I apply the direct formula (SWR=maximum voltage/minimum voltage) to the square wave displayed on CRO ?

Click to expand...

Back to original question.
If you set up VSWR measurement system using Slotted-Line, Detector, DUT and Storage Oscilloscope correctly, you have to take root of a displayed wave since it is a square wave created by square-detector.

Please refer to this http://wireless.ictp.it/handbook/C3.pdf There is a setup for VSWR measurement.

lucy123 said:

Please refer to this http://wireless.ictp.it/handbook/C3.pdf There is a setup for VSWR measurement.

Click to expand...

This is a common TDR which every one knows.
The Designer's Guide Community Forum - Frequency Response using a TDR
Time-domain reflectometer - Wikipedia, the free encyclopedia

But I don't think a figure which a starter of this thread shows is for TDR, although there is a CRO.