Author Topic: DS1054Z show amplitude in dBm with ref impedance?  (Read 821 times)

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Online bd139

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DS1054Z show amplitude in dBm with ref impedance?
« on: August 24, 2017, 08:31:03 PM »
Is it possible to get the DS1054Z to show amplitude in dBm? I'm terminating with a 50R feed through at the scope channel input.

My DG1022Z allows output drive to be specified in dBm into a reference impedance of 50R. Was wondering if I could do the same with the scope at the other end. Would save me some legwork with the calculator!
 

Online bd139

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Re: DS1054Z show amplitude in dBm with ref impedance?
« Reply #1 on: August 26, 2017, 02:48:10 AM »
Done this the hard way.

I wrote a simple-ish SCPI client in C# for the DG1054Z. This reads the Vpp reading from channel 1, does the relevant maths on it and displays it on a windows forms app once a second :)
 
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Offline MattSR

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Re: DS1054Z show amplitude in dBm with ref impedance?
« Reply #2 on: August 31, 2017, 06:32:43 PM »
Did you connect via USB or ethernet just out of interest?
 

Online bd139

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Re: DS1054Z show amplitude in dBm with ref impedance?
« Reply #3 on: August 31, 2017, 07:47:37 PM »
Ethernet. USB doesn't really assume a "protocol" and requires drivers. The ethernet mode uses TCP/IP so you can just effectively telnet to the port and issue commands.
 

Offline MattSR

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Re: DS1054Z show amplitude in dBm with ref impedance?
« Reply #4 on: September 03, 2017, 09:01:24 AM »
I thought that might have been the answer. I see USB as being the "hard way" since it doesn't have a defined protocol like TCP/IP or GPIB for example.
 

Offline Neganur

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Re: DS1054Z show amplitude in dBm with ref impedance?
« Reply #5 on: September 03, 2017, 09:51:42 PM »
Does the rigol support advanced math functions?
If so maybe you could just use a user defined function

I looked at the user manual but it wasn't clear to me if you could combine the functions or just use them individually:


Math Operation
DS1000Z can realize various math operations (including: addition (A+B), subtraction (A-B), multiplication (AxB), division (A/B), FFT, A&&B, A||B, A^B, !A, Intg, Diff, Sqrt, Lg, Ln, Exp and Abs. The results of math operation also allows further measurement (for details, please refer to “Cursor Measurement”).
Press     ? Math ? Operator in the vertical control area (VERTICAL) at the front panel to select the desired operator. The result of math operation will be displayed on the waveform marked with “M” on the screen after you press Display to enable the operation.
 

Online bd139

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Re: DS1054Z show amplitude in dBm with ref impedance?
« Reply #6 on: September 04, 2017, 02:24:40 AM »
I couldn't work the math functions out to be honest :)
 

Offline abraxa

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Re: DS1054Z show amplitude in dBm with ref impedance?
« Reply #7 on: September 04, 2017, 04:01:10 AM »
does the relevant maths on it

Mind sharing? A quick search only showed calculators, tables and approximate values for sinusoidal waveforms.
 

Online bd139

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Re: DS1054Z show amplitude in dBm with ref impedance?
« Reply #8 on: September 04, 2017, 04:28:57 AM »
Off the top of my head, you'll have to fill in the gaps

1. Convert reference power (1mW) into volts RMS in 50 ohm system: ref = sqrt(P*R)
2. Convert sample voltage into RMS: sample = (vpp/2)*.707
3. Divide one by the other ratio = sample/ref
4. Take log of it: ratio = log(ratio)
5. Multiply by 20: dBm = 20 * ratio.

Disclaimer: haven't actually checked the above, just tapped it out quick. the program I have is tested but I don't ahve access to it at the current time.
« Last Edit: September 04, 2017, 04:31:02 AM by bd139 »
 


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