AnsweredAssumed Answered

8720ES weak power at Port2

Question asked by dac_agilent on Dec 13, 2011
Latest reply on Dec 15, 2011 by dac_agilent
Hello!

I'm using quite old, but very good VNA 8720ES model. Equipped with 400 & 089 options.
During test, probably high power have come into Port2.

Now it works, no errors, but output power from Port 2 is too weak.
So it affects on S12 and S22 readings. S11&S21 normal.

Both attenuators switching, bias network and directional couplers seems to be OK.
Samplers also seems to be OK.

When Port1 on, with Pout=0dBm for example, and I measure R, I can see ~0dBm readings. It's OK.
But with Port2 on I measure (internally) about +3dBm, while real Port2 output power is -30..-20dBm.
Problem occurs in all the bandwidth.

I have measured output power from A74 "switch splitter assembly" J5 output coming to A71  attenuator and it fails (-20dBm and less while 0dBm set).
Also +3dBm reading on R input port when Port2 on and power set to 0dBm, seems to be associated with splitter faulty.

update: get switch out of the VNA and measured.
Port1 -6dB (@1GHz) to attenuator and -26dB to R1
Port1 -37dB (@1GHz) to attenuator and -23dB to R2


This VNA's support was finished.
Splitter assembly 5086-7975 can not be ordered, can not be sent to repair (I requested).

Can somebody advise any suggestions for repair?
I want to repair splitter (and probably replace only 1 of resistors in 2nd splitter).
Also It seems to me that I can replace 1 of resistors in splitter with the "jumper" (transmission line) and connect external splitter to one of the outputs (J4 or J5).
Another solution is to replace switch splitter assembly with switch+splitters.
The only thing that is not clear: should it be the switch with open unused output (reflective) or terminated (to 50Ohm) or terminated via capacitor (working not from DC, but from Fmin>0) or unused output should connects to ground?

And as for repair: I'm able to ask for chip mounting and wire bonding for chip elements.
1)I just want to now: switch-splitter is germetically sealed on not? Updated - it's not sealed, just dust proof.
2) What kind of components can be used to replace splitter and probably switch (resistors and pin-diodes)?
3) How it is driven?

I don want to reach original performance, firstly I want to bring life to the instrument.  

Outcomes