@2N3055,
Thank you for replying.
You affirmed:
“I have to admit that I have a bit of trouble understanding you.”
Ok. You don't have an MSO from the MSO5000 family. And it cannot reproduce the essay.
And, I have to admit, understanding the command sequence or flowchart to get the FFT-AM on the MSO5000 is not that simple. It is necessary to go through the difficulty to reach some satisfactory result.
As for the quality of the SDS1204X-E and MSO5000 are not being tested. What I want is to understand how the MSO5074 works, and trust the results of its measurements.
I don't have an external SG or AWG, or the SDS1204X-E. The SDS1204X-E does not have the internal SG. There is the accessory, or you must buy a professional external SG.
The MSO5000 has an internal SG, limited to SINE = 25MHz and SQUARE = 15MHz.
The one I can use right now is MSO5074. Which in my opinion is excellent and functional.
Just learn to use the commands in the correct sequence.
@2N3055, Your comments are relevant, thank you very much.
@gf,
Thank you for replying.
Your questions are relevant, but they are the “initial question data”, which was asked so that anyone who has an MSO5000 can reproduce the essay.
Note “Item 9” of the Initial MSG.
You affirmed:
1. “Is the carrier voltage of 500mVpp the no-load voltage, or the voltage with 50 Ohm termination?”
The MSO5000 SG G1/G2 has programmable signal output in 50 Ohm and HighZ. I fixed on HighZ. But changing to 50 Ohm, there is no change in measurement.
The ORIGINAL CONDITION: To generate in SG-GI/GII in MSO5000:
Carrier Sine Signal f = 1MHz, with Vpp = 500mV, and Audio Modulator Sine f = 10 KHz, with AM Depth = 80%.
2. “How is the signal probed?”
- direct connection into scope input, input set to 50 Ohm?
- direct connection into scope input, input set to 1M Ohm?
- high Z 1:1 probe?
- high Z 10:1 probe?”
External connection (G1/G2 to CH-1) can be done through the original Probe in 1:1. Or via 2 x BNC connector with cable.
3. “Is the same probing used with both scopes?”
No. I only have one MS5074 with the original probes. I don't have the SDS1204X-E.
Note "item 4" of the Initial MSG:
“For Measuring the Modulation Index of an AM Signal using an FFT, I found an application note for the SIGLENT SDS 1204X-E, here:
https://siglentna.com/application-note/measuring-the-modulation-index-of-an-am-signal-using-an-fft/?pdf=9065”
4. “dBV is not necessarily a unique specification. It can be interpreted as either dBVeff, dBVpeak or dBVpp. So dBV numbers from different origins may not be comparable, but there can be a difference of 3, 6, or 9 dB. Still both can be correct, but just interpreted differently.”
@gf, The “Unit” of the FFT on the MSO5000 can be set to: “dBm/dBV or Vrms”.
@gf, I read about dBV, and it's the RMS measure. See article: 0 dBV = 1 Vrms:
https://reference-audio-analyzer.pro/en/v-dbv-dbu.php#gsc.tab=0@gf, your comments are relevant, thank you very much.
@TurboTom,
Thank you for replying.
You affirmed:
“... I dare to disagree. The DG800/900 series is an arbitrary waveform generator, not an RF signal generator. Hence, Rigol makes sure that the absolute momentary signal amplitude doesn't exceed the specified figure (voltage/level). In case of an AM signal with fixed carrier, this would be the case (by 6dB) if the carrier stays at the same level as in unmodulated operation. There has been a lot of argueing going on on that topic. In the most recent firmware revision for the DG800/900/2000 AWGs, Rigol has changed the math model (variable carrier when changing AM depth) for a reduced but fixed level carrier (6dB below unmodulated), thus limiting the 100% modulated output amplitude to the preconfigured level. IMO, this approach is valid and reasonable in case of a waveform generator, it only should be properly documented and specified. Obviously, in case of an RF signal generator, the carrier can be expected to stay constant, regardless if the signal is amplitude modulated or not.
It's well possible that Rigol took the same approach in case of the DS5000's integrated AWG, but that's an assumption since I haven't got any experience with this instrument. Regarding the DG800/900/2000 series of AWGs, your bashing is not legit -- these are pretty decent instruments, especially considering the price of the entry level model after the hack.”
Quanto à série DG800 / 900. Eu não possuo um exemplar. Não posso comentar.
Quanto se deve ser documentado os parâmetros do SG para geração de sinal e medições, eu concordo com você:
As for the DG800 / 900 series. I do not own a copy. I cannot comment.
When it comes to documenting the SG parameters for signal generation and measurements, I agree with you:
“in case of a waveform generator, it only should be properly documented and specified”.
@TurboTom, your comments are relevant, thank you very much.
@seronday,
Thank you for replying.
@seronday, your comments are relevant, thank you very much.
You affirmed:
“@BRZ.tech
You need to be aware that the MSO5000 Generator output voltage level is reduced by half (6dB), when amplitude modulation is selected.
The User Manual makes reference to this under " Set the Modulation Depth "
This change in level can be observed as follows:-
Monitor the Generator output.
Select Amplitude Modulation.
Set the modulation level to 0 percent.
Turn the modulation On and Off.
I assume that this has been done so as to not overdrive the Generator output stage on modulation peaks, when the output level is set to maximum.
So to reproduce the Siglent test that you refered to it would be necessary to to set the MSO5000 Generator output to 1V P/P,
Regards”
I made your suggestions, and took the pictures, with Carrier = Amplitude = 1Vpp on MSO5074.
1. Carrier without Modulation: around Vpp = 1.0359V.
2. Carrier with Modulation, with AM Dept = 0%: Around Vpp = 513.12mV.
Note that Carrier with Modulation has dropped almost by half, as per the User Manual: 1.0359V -> 513.12mV.
3. Carrier with Modulation, with AM Dept = 80%: Around Vpp = 929.43mV. So, the Vpp of the AM modulated signal on the MSO5074 was around 1Vpp.
4. The “Surprise” in the FFT measurement was to multiply by 2x the 500mV Vpp of the SG signal in the MSO5074, to 1Vpp.
The FFT measurements on the SIGLENT SDS1204X-E, for Carrier = 0.5 Vpp, are (according to the SIGLENT article):
Carrier: f = 1.00 MHz / -14.9dBV, LSB: f = 990 KHz / -22.8dBV, USB: f = 1.01 MHz / -22.8dBV.
6. The FFT measurements at MSO5074 for Carrier = 1Vpp, are:
Carrier: f = 1.00MHz / -15.15dBV, LSB: f = 990.01KHz / -23.7dBV, USB: f = 1.099MHz / -23.03dBV
It can be seen that the FFT measurements on the MSO5074, with Carrier = 1Vpp, were very close to the measurements offered by the SIGLENT SDS1204X-E test (with Carrier = 0.5Vpp -> see the article on the SIGLENT link).
In the case of Carrier:
MSO5074 = -15.15dBV
SDS1204X-E = -14.9dBV
The difference between measurements being (-15.15 – (-14.9)) = -0.25dBV = 971.6 mV.
Here, a dBV to Volt converter, enter -0.25dBV:
http://www.cantwellengineering.com/calculator/convert/dBV