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changing channels for P93XX VNA with SCPI

Question asked by BillEaton on Aug 14, 2019
Latest reply on Aug 15, 2019 by daras

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I'm making my own pyvisa driver for some P9371A VNAs we recently purchased.

The help file indicates in at least one place that there is no good way to turn channels on and off with SCPI commands(note None in table below copied from help file):

CF_Channel Commands

Channel 1 - 8 Tab Commands
Softkey	Sub-item	SCPI
Channel 1	On/Off	None
Channel 2	On/Off	None
Channel 3	On/Off	None
Channel 4	On/Off	None
Channel 5	On/Off	None
Channel 6	On/Off	None
Channel 7	On/Off	None
Channel 8	On/Off	None

Are there any plans to update this SCPI functionality? It seems like channels are close to unusable with SCPI. But yet, quite a few commands take cnum (channel number) as a parameter.

As a work-around, it looks like I could abandon channels altogether and instead manipulate traces and windows. But even that does not seem to be as straightforward as one might hope...

daras

Aug 14, 2019 6:12 PM

Correct Answer

I am guessing that you are talking about the act of turning channels on and off from the front panel as shown in the GIF above. From the GUI, turning on a channel is a one-click operation but from SCPI that is actually a combination of 3 different commands:

1- create the S11 measurement in the channel you want (example channel 2):

calc2:par:def:ext "somename", "S11"
(note that the above command is for creating a measurement in a standard S-Parameter channel. for other application channels, like SMC, you'd have to use calc<ch>:par:cust:def)

2- Select the measurement:

calc2:par:sel "somename"

3- put the new measurement trace in the window you want to display it in:

disp:wind1:trac2:feed "somename"
(there are two assumptions here:
1- the window that you want (i.e. window 1 in this case) is already on
2- you know that this measurement is going to be the 2nd trace in that window (i.e. trac2)

now to delete the channel, you have to delete all the measurements that are associated with that channel. for that there is a single command (again using channel 2 as the example):

calc2:del:all

so this is not a missing SCPI functionality, just a difference in operating theory between the GUI and the remote API

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daras

Aug 14, 2019 6:12 PM

1- create the S11 measurement in the channel you want (example channel 2):

calc2:par:def:ext "somename", "S11"
(note that the above command is for creating a measurement in a standard S-Parameter channel. for other application channels, like SMC, you'd have to use calc<ch>:par:cust:def)

2- Select the measurement:

calc2:par:sel "somename"

3- put the new measurement trace in the window you want to display it in:

disp:wind1:trac2:feed "somename"
(there are two assumptions here:
1- the window that you want (i.e. window 1 in this case) is already on
2- you know that this measurement is going to be the 2nd trace in that window (i.e. trac2)

now to delete the channel, you have to delete all the measurements that are associated with that channel. for that there is a single command (again using channel 2 as the example):

calc2:del:all

so this is not a missing SCPI functionality, just a difference in operating theory between the GUI and the remote API

1 person found this helpful

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BillEaton @ daras on Aug 15, 2019 6:18 PM

Thanks for making me think about it some more. I guess what always throws me off is the idea that I have to come up with a measurement name. Maybe there are some advantages in speed to do it this way. Maybe having measurements predefined makes it faster, for example, to switch between S11, S21, etc.

Suggest edit for last command. Should be

CALC:PAR:DEL:ALL

Inserted PAR and deleted : It seems there is no option for DEL:ALL per channel. Also if you execute this command, all windows, all traces, all channels get turned off and then you have to go to the Add Window commands. Probably it would be preferred to delete specific measurement names.

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daras

@ BillEaton on Aug 15, 2019 7:05 PM

First, thanks for catching my type-o. it is supposed to be calc:par:del:all.

as for this comment:

BillEaton wrote:

Thanks for making me think about it some more. I guess what always throws me off is the idea that I have to come up with a measurement name. Maybe there are some advantages in speed to do it this way. Maybe having measurements predefined makes it faster, for example, to switch between S11, S21, etc.

the meas name requirement is a hold over from much earlier version of the firmware and I'd be hard pressed to come up with a good reason for it. in the latest versions developed for B model PNAs and the new PXI/USB modules, we have introduced a parallel track of commands:

CALCulate<cnum>:MEASure<mnum>:....

with these commands you can do all the stuff you did with CALC:PAR commands and you don't have to specify a meas name, just a meas number. if you are interested in learning more about these commands, you can look at the "VNA B model " online help here.

BillEaton wrote:
Also if you execute this command, all windows, all traces, all channels get turned off and then you have to go to the Add Window commands. Probably it would be preferred to delete specific measurement names.

you can delete specific parameters by using the calc:par:del <meas name>, I just mentioned the delete all because it is the closest thing to turning the channel off from the front panel.

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3 Replies

daras Aug 14, 2019 6:12 PM
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Correct Answer

I am guessing that you are talking about the act of turning channels on and off from the front panel as shown in the GIF above. From the GUI, turning on a channel is a one-click operation but from SCPI that is actually a combination of 3 different commands:

1- create the S11 measurement in the channel you want (example channel 2):
calc2:par:def:ext "somename", "S11"
(note that the above command is for creating a measurement in a standard S-Parameter channel. for other application channels, like SMC, you'd have to use calc<ch>:par:cust:def)
2- Select the measurement:
calc2:par:sel "somename"
3- put the new measurement trace in the window you want to display it in:
disp:wind1:trac2:feed "somename"
(there are two assumptions here:
1- the window that you want (i.e. window 1 in this case) is already on
2- you know that this measurement is going to be the 2nd trace in that window (i.e. trac2)

now to delete the channel, you have to delete all the measurements that are associated with that channel. for that there is a single command (again using channel 2 as the example):
calc2:del:all
so this is not a missing SCPI functionality, just a difference in operating theory between the GUI and the remote API
1 person found this helpful
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- BillEaton @ daras on Aug 15, 2019 6:18 PM
  Mark Correct
  Correct Answer
  Thanks for making me think about it some more. I guess what always throws me off is the idea that I have to come up with a measurement name. Maybe there are some advantages in speed to do it this way. Maybe having measurements predefined makes it faster, for example, to switch between S11, S21, etc.
  
  Suggest edit for last command. Should be
  CALC:PAR:DEL:ALL
  Inserted PAR and deleted : It seems there is no option for DEL:ALL per channel. Also if you execute this command, all windows, all traces, all channels get turned off and then you have to go to the Add Window commands. Probably it would be preferred to delete specific measurement names.
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  - daras @ BillEaton on Aug 15, 2019 7:05 PM
    Mark Correct
    Correct Answer
    First, thanks for catching my type-o. it is supposed to be calc:par:del:all.
    
    as for this comment:
    BillEaton wrote:
    
    Thanks for making me think about it some more. I guess what always throws me off is the idea that I have to come up with a measurement name. Maybe there are some advantages in speed to do it this way. Maybe having measurements predefined makes it faster, for example, to switch between S11, S21, etc.
    
    the meas name requirement is a hold over from much earlier version of the firmware and I'd be hard pressed to come up with a good reason for it. in the latest versions developed for B model PNAs and the new PXI/USB modules, we have introduced a parallel track of commands:
    CALCulate<cnum>:MEASure<mnum>:....
    
    with these commands you can do all the stuff you did with CALC:PAR commands and you don't have to specify a meas name, just a meas number. if you are interested in learning more about these commands, you can look at the "VNA B model " online help here.
    
    BillEaton wrote:
    Also if you execute this command, all windows, all traces, all channels get turned off and then you have to go to the Add Window commands. Probably it would be preferred to delete specific measurement names.
    you can delete specific parameters by using the calc:par:del <meas name>, I just mentioned the delete all because it is the closest thing to turning the channel off from the front panel.
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changing channels for P93XX VNA with SCPI

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