Which command group to retrieve the specturm measurement results of MSO44?

Hello All,
I didn't find out the correct command to read out the measurement result. do you have any suggestion? thanks.
The measurements are channel power, ACPR, OBW.

Hello Jeremy,
You would typically use the same commands to recall any other measurement result:
MEASUrement:MEAS<n>:RESUlts:CURRentacq:MEAN?
where <n> is replaced with the relevant measurement number.
However, it does appear that there is a bug in the firmware that is returning in invalid response. This has been reported to our engineering team.

Hello Alan,

Thanks for the help.

 I have another question about the channel power since I could not recall the value.

Could you help to advise how can we calculate the channel power when we get the waveform of the spectrum view.
（edit: after study,It seems we could not calculate the channel power only according to the spectrum view? am I correct?）

 I don't know how to update the attachment. so I will put what I have found in the next reply.

And how can we set the measurement to read channel power programatically.
I didn't find out the type in the argument list (P2-874). I can set the measurement to TOP, peak to peak,Base

here is another picture for what I have found.

don't know why the post easily to be messed up by the symbol， but sometimes it is ok.

Hi Jeremy,

The image you attached is also the algorithm used by the scope (page 635 in the MSO4 help manual).
Looking at the equation, the values that you need to calculate channel power would be CBW (channel bandwidth), RBW (resolution bandwidth), N (number of data points) and Pk (power at the kth data point.)

• To set/query CBW (the difference between the upper and lower frequency)
  CHx:BANdwidth
  Correction:  MEASUrement:MEASx:CPWIDTh
• To set/query RBW (must set RBW mode to manual first)
  SV:RBWMode MANual
  SV:RBW
• To find N and Pk, you could save the spectrum data and then parse through each point. The Save and Recall command group (2-92 in Programmer Manual) should have the SCPI commands to set up where to save and such. You can also change the record length;
  HORizontal:MODE:RECOrdlength
  You can look more at the acquisition or data command group for other parameters you might want to change.

Hopefully this will be a good starting point. I will let you know if I have any more ideas for working around the bug or edit if I find some more suitable commands for finding this programmatically. 

-Iris

Hello Iris,
Thanks. understood the N and Pk could be found out according to the spectrum data. 

It seems I was able to get the value very close to the value show on the scope screen. but always a bit deviation, no matter I update the CBW or not.

here is another question. I'm not sure how to calculate the N exactly in the scope. because the data point interval frequency(here df=52.6316Hz) from the spectrum data alway to be a floating value instead of the integer. I need to calculate N by CBW/df, it could be a floating value. should I do it round to the nearest integer or what..  it seems when the calculate result is x.5, the deviation is the maximum.

probe compensation source, center frequency 9k Hz, SPAN 40K Hz, RBW:100 Hz.  CBW:1000 or others
Start_Frequency  0
Stop_Frequency   29000
increment  52.63158971
samples    552
 

And for how can we set the measurement to read channel power programatically.

MEASUrement:MEAS1:TYPe (I mean what string to input here ), or is that means do not support spectrum measurements in this group?P2-874
 

Hi Jeremy,

We were able to replicate your issue with the channel power measurement where the result calculated by the scope is mismatched from what we calculated with Excel by about 0.2 dBm. We are currently working with our product line to understand this issue.

I don't have an authoritative answer to your question about N, it might be the source of the measurement discrepancy discussed above.

 

_{CBW should be channel width instead of bandwidth limit?}

Yes, channel width is the relevant number to channel power calculation. The SCPI command is MEASUrement:MEASx:CPWIDTh


The measurement type is CPOWER, as defined on page 2-886.

Hello Teles,

Thanks for the feedback. it seem the calculation result is the same between us.

N may have a bit impact on the calculation. but it seems not the key factor of the deviation.
and thanks for the command MEASUrement:MEASx:CPWIDTh.

Thanks for the help always.

Hi,<br> <br> I was wondering if there has been a fix to read out the measurement for the channel power?&nbsp; I am attempting to record channel power remotely using SCPI, but I am receiving incorrect measurements reported back.<br> <br> - I am measuring the power of Channel 8 using Spectrum View on Measurement 1<br> - The badge is present on the screen, showing ~ -100dBm<br> - Command sent: &lt;code&gt; MEASU:MEAS1:RESU:CURR:MAX? &lt;\code&gt;<br> - Response to Query: "9.91E+37"<br> <br> Any help would be appreciated!

Hi James,

The error me and Jeremy were discussing was very small.
The error you have there is likely because you are querying the max value. Instead you'll want to use  measu:meas1:resu:curr:mean? or, to get the current value, you can use the measurement:immediate group of commands.

Hi Afonso,
Oops, after that, I didn't try to read the value again. it seems I couldn't find the CPOWER type on Page 2-886, the page is about MEASUrement:MECH:GRATio.  and does the command MEASUrement:MEASx:CPWIDTh not in the manual?

I didn't find the instruction for measurement:immediate in the manual. Are we talking about the same version of manual 077-1305-17?

Hi Jeremy,

The version I am referring to is 077-1305-18, which is the latest currently available on our website: https://www.tek.com/en/sitewide-content/manuals/4/5/6/4-5-6-series-mso-programmer-manual  

The command you want is measu:meas1:type cpower.
measu:measx:cpwidth is on page 2-772 of the latest manual.

I apologize, the command group is measurement:immed , not measurement:immediate