Jeremy Li

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.

Dear all,
1. Is it possible to transfer both analog waveform data and spectrum view data in one trigger event?(MSO 4 Series)  if yes, how should I do, how to input the string after DATa:SOUrce<?>

I tried to fetch（CH1,CH2) and then fetch SV (CH1_SV_NORMal, CH2_SV_NORMal data), but it seems only able to fetch one sv data, and I still not sure if the SV data corresponding to the channel and current analog data.  

 2. How can I know how many data points(DATa:STOP)  should I set for the curve? command to fetch SV data.  the MDO 3 series is a fixed 750 data points in the mannual.

3.  Should I use 10*log(1000 * x)  to calculate the SV (CH1_SV_NORMal) DATA? the output seems didn't match what I have saw on the scope screen.

Hi Teles,

Thanks for the information.

May I ask if the bandwidth of the RF input channel in 3 Series MDO models is normally higher than the 4 Series MSO models?

Is the Spectrum View of 4 Series MSO models(MSO44)  type of scopeFFT? Or it is same as the built in RF channel of 3 Series MDO with different kind of probe?

Dear All,

The Tektronix 3 Series MDO models have a built-in RF input,while  4 Series MSO modes don't have this input.

 3 Series MDO (RF Commands ) , 4 Series (Spectrum View commands)
As described in the  3 Series MDO programmer manual:
MDO instruments calculate Fast Fourier Transform calculations (FFTs) with
a 1,000 to ~2,000,000 point output, depending on the acquisition settings. It
then reduces that FFT output into a 750 pixel-wide display

Is that means the RF function could be calculated according to the measurement of CH1-CH4 channels even we don't have RF input on 3 Series MDO models.

Could someone tell me more about the difference,  thanks in advance.

Hi 
I found the MSO44/46 also have issue when connecting via USB, it seems the "CLEAR" command would make them stop response. but via LXI, they seem working well. even if I was able to capture data from the scope, it is easily lose communication when connecting via USB.