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Garbage collected if 8753ES & 8720D are on adjacent GPIB addresses

Question asked by drkirkby on Feb 15, 2016
Latest reply on Feb 16, 2016 by drkirkby
I had the following two VNAs on a GPIB bus. 
* 8720D on GPIB address 16 (firmware 7.74, October 30 ^th^ 2002)
* 8753ES on GPIB address 17 (interestingly the same version and date on the firmware) 
If one of the two VNAs is powered on, then the software is able to read from that VNA and save the data. However, if both VNAs are on, then whatever one is addressed, the other one says 

"CAUTION: ADDRESSED TO TALK WITH NOTHING TO SAY"

I'm puzzled why this should happen. I know the VNAs have other things like printers, plotters and power meters, but those are either disabled, or are not on conflicting GPIB addresses. 

I decided to move the 8753ES to address 20. After this, there are no problems. 

I'm puzzled why these two VNAs don't want to be friends if on GPIB addresses 16 and 17. I've not done any detailed checks about exactly what addresses will or will not work, but having one on 16 and the other on 20 is ok, but 16 and 17 are not. 

I don't think the software is at fault, as it was written by a brilliant but modest programmer (me)!!! It command line driven stuff, written in ANSI C, so the following code gets S11 data in log magnitude/angle format from GPIB address 16 and saves it in a Touchstone file. 

drkirkby@buzzard:~$ vna --log --s11 --s1p 16  > data-from-8720D.s1p
drkirkby@buzzard:~$

It is running on an old Sun Blade 2000 Unix workstation running Solaris 10. The GPIB card is a National Instruments one on a PCI card. There's no MATLAB/Vee/LabView or any other GUI. So a pretty unusual hardware/software setup, but I'm still puzzled while these two VNAs don't seem to be buddies if on adjacent GPIB addresses. 

Dave  

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