Jeremy Li

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

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.

Hi Teles,
It works, thank you very much.

Hi Teles,
Thanks, just understood that the command MATH:MATH2:VUNIT? is to read the unit of what user defined.
I intend to fetch the unit for the Y-axis label name. 
for example , the unit for MATH2=INTG(CH1*CH2) display on the scope screen is uj or mj, how can I retrieve this kind of string?

Hi All, Or It seems I should  say, Hi Teles, ：-）

I'm tring to retrieve the Units  Manual P2-367 for the Math results,for example:MATH:MATH2:VUNIT?

But I always get "" instead of the correct units.

Could you help to advise what is wrong with my program or what is wrong with the scope setting?

Hi Teles,
Thanks for you patience, according to your instruction, I have find out the answer in LabVIEW help document.

magnitude is the magnitude of the averaged FFT spectrum. If the input signal is in volts (V), magnitude has units of volts-rms (Vrms). If the input signal is not in volts, magnitude has units of the input signal unit-rms. If dB On is TRUE and the input signal is in volts, magnitude has units of dBV

So what I got was dBV ,and 14.01dBm seems close to the scope.

Hi Teles,
Thanks for the reply. it seems we need to set data width to 8 when transfering FFT data on MSO2. But it is ture that we don't need to set the data width on MSO4 spectrum view when using dB unit.

Here I come up with another question which confuse me for a long time.

I connected the probe to the probe compensation source. and we could have a 2.5V square wave. 
When doing FFT transfer, we could know that the most strength frequency is 1K Hz. and then other frequency 3k,5k... but as shown on the scope screen, the 1K Hz frequency is always about 13-14dBm, how can we calculate to have this value.
Is there some relationship with Vrms unit.

because when doing FFT on LabVIEW, the 1K Hz is always near to 0 dBm while the delta dB between different frequency seems correct. it seems some kind of offset between the calculation.

Spectrum View: A New Approach to Frequency Domain Analysis on Oscilloscopes | Tektronix

this document seems have some help on understanding the difference.

Hi Teles, 
Thanks, now it is clear for me, I should not apply a log function to this data as it is already in log form.
I'm using LabVIEW for the programming, and I should take care of the data width as in your script scope.write("dat:width 8").

Hi Teles,
Thanks for the instruction.
1.  I have updated the timeout setting and it seems ok now. I am not able to try it on MSO 4 series currently. I try the Math function on MSO2 instead.
2.  I was thinking if the data points is fixed if I want to read all the points. such as MDO 3 Series. it seems the data points will be different with different data length on MSO4, am I correct?
3. I will try it later when I have the chance to get close to the instrument, thank you so much for the help.