# ENA5071C absolute measurments

Question asked by aleberto69@gmail.com on Mar 11, 2014
Latest reply on Mar 26, 2014 by aleberto69@gmail.com
I need help about Absolute Measurement with ENA 5071C.
I refer to the direct access to the absolute R1(n) R2(n) ... A(n), B(n) measurements ( n being the port where the stimulus is applied)  ( measurement menu).
I tried to perform some " special" calibrations using that parameters and together with the math capability of the instrument, instead of using normal S parameters.. Unfortunately my algorithms didn't work as I would have expected.
After investigations I found some inconsistency about what I suppose that  the absolute measurement  are.
Namely
1) I used just port 1 and port 2 ( so that R1,A,R2,B are the involved measurements)
2) Connect port 1 and 2 with a 50 ohm cable ( 1m) and perform measurement at about 100 MHz ( few points to easily verify the results)
3)I measured  R1(1), A(1),R2(1) and B(1) and  normalize the 4 measurement to the value of the first one ( R1(1))

so that...
-R1(1)/R1(1) is 1  (obvious)
- as expected B(1)/R1(1) is in modulus close to 1 ( signal propagating through the cable and entering in port 2)
- as expected A(1)/R1(1) is small ( representing the reflected wave coming back into port 1) supposing this means that port 2 is rather matched (load match)
- as I didn't expect R2(1)/R1(1) result in modulus about 0.4 instead to be rather small ( as A(1)/R1(1))..

If R2(1)/R1(1) is proportional to the wave outgoing from the port2 ... I could understand that this could at least be not small...( It means that the port is not well matched) but in this case I also expect A(1)/R1(1) to be similarly not small as well ..

Identical things happens using other ports and in all the possible Direction" ( stimulus position)

With this inconsistency is it now clear why my algorithm is not working properly.

In the ENA 5071C manual there is just a brief mention to those measurement with very few explanation..

There is also another mystery...

Why the above 4 parameters  are not constant in phase from sweep to sweep?
I could verify that the relative phase is stable ( after normalization the phase is stable from sweep to sweep), but is not clear why it isn't stable the absolute phase of each of them...
"May be an architectural question" I told myself .....

Thank you in advance to everybody...
Regards
Aleberto69