I have my Friday’s questions for the weekend to relax with…
· 1-port method - I do see that the Bode100 monitor both the voltage ahead of the reference source resistor and after the source resistor:
o Why monitoring the voltage ahead of the internal resistor?
o Is it because this voltage is the some of the Voltage source and the reflected one?
o We do have Zref*(1+S11)/(1-S11)… As we are measuring voltage, what is S11 in this case?
· 2-port shunt through - here the Bode100 monitors the voltage ahead of the DUT, without monitoring the voltage ahead of the reference source resistor:
o Is the voltage seen at channel1 the sum of both incident and reflected voltage?
Hope you can clarify my doubts.
This effectively measures the current in the 50 and Ohm resistor and the voltage at the port. Z) V/I. The Bode 100 doesn't actually measure the S parameter S11, though computes is by solving the reflection equation you are showing. They know Zref (50 Ohms) and they know Zdut (V/I) so they can compute S11 ;)
In the 2 port, they don't need to measure the current. They know the voltage before the 50Ohm resistor and also at port 2.
Z=25*S21/(1-S21). S21 is determined from the voltage before the 50 Ohms and at port 2, so no need to measure port 1. Not sure that image is right, since we don't use CH1 for the 2 port measurement.
I do realize that the picture I have put is not the setup for the 2-port shunt through but it is for the gain/phase measurement…
With the Bode100, we do look at the voltage ahead of the Zref and the voltage across the DUT.
With the scope, we cannot see the voltage ahead of the Zref, so we use the port replicator to measure the voltage after the Zref, but using the active splitter you have, we do not lose the 6dB, so all the formulas are still valid!!!
The passive splitter software option takes into account this loss!!!
Am I correct?
Correct. And a 3 resistor Splitter has no isolation, which is bad, so should generally us a power divider. J2161A does this without loss and with much better isolation. It also is semi-differential, so it eliminates the noise from the several measurement grounds. For example AFG ground in the rear of the scope, channels at the front of the scope and ground at the DUT.
Thank you, Steve!!!
I am preparing a training for my European colleagues:
Your lessons are fantastic!!!
Thanks for the compliment, glad you like the class.