Oscilloscope help

[Performa01]

Any kind soul willing to put a 4mvpp 4MHz sine wave signal amplitude modulated by 10mvpp 50KHz triangle signal, with a random 20Mhz 50mvpp noise to their GW instek 1054B or Siglent 1104X-E ? I really want to see whether the GW instek can do better with its digital filter, or Siglent can trigger reliably showing me the 4MHz signal. Also I need it to be as close to realtime as well, so vary the 4MHz signal and see if the digital filter or the triggering setting actually cause a massive delay.... a delay of about 200-300ms should be tolerable, 1s delay is bad...

I would gladly do that, but you'd have to wait until the weekend.

I did a similar test last weekend though.

2mVpp sine signal at 750kHz plus 2mVpp 5.9MHz sine, 80% amplitude modulated by 10kHz.

No problem getting a stable triggering on this signal mix with just a little trigger level tweaking. If everything else fails, the correct holdoff time gets rid of any spurious triggers.

First display with intensity grading:


SDS1104X-E Noisy Signal IG

Now with color grading:


SDS1104X-E Noisy Signal CG

Finally an FFT analysis, which clearly shows the signals involved. You even get a reasonably accurate frequency indication by the peak marker table:


SDS1104X-E Noisy Signal FFT

EDIT: A "4mvpp 4MHz sine wave signal amplitude modulated by 10mvpp 50KHz triangle signal" sounds a bit far fetched. This would be 250% modulation and no waveform/signal generator can do that.  I think you should provide a more serious specification of what signal you actually want to see…

Furthermore, with 50mVpp noise you essentially want to look at a tiny signal totally buried in interference and noise. The CRO cannot give a meaningful result with this and your screenshots did not show something nearly as bad as that. The DSO on the other hand can clearly separate and analyze all these signals by means of a powerful FFT, as demonstrated above.

[2N3055]

@ultrasmurf, do you mean modulated or superimposed (added, as in spurs bleeding from the side)? Also, 20 MHz noise, does that mean noise band limited to 20MHz max ?

[ultrasmurf]

Thanks for the image Performa01. Yup, I guess I spec the noise without thinking. Attached is the previously uploaded noise captured in the DSO. It shows a sort of 10mvpp, but there is a 4mvpp signal in there, so the noise amplitude is more like 6mvpp. I didn't take time to average the freq measurement, DSO says 57KHz, CRO says 52KHz. It might be a FM 5khz signal on a 55KHz carrier (which sounds like an SMPS power supply doing their best).

2N3055, I'm not sure what to say about the 20MHz noise, it's random, and shaped sort of like an impulse respond signal. It's of lower worry for me as even with the Hantek I can tune this one out. Or even if it's showing up, due to it's less occurence, it doesn't really push my signal out.

[ultrasmurf]

So I have a little free time today to further dig into the noise. The 20MHz noise is coming from my soldering iron at sleep ( I never really turn my soldering iron). So it's easily removable. The other noise is coming from the HV power supply that comes together with the dut, so it will be there when I need to look at my signal. Without any load it is stable at 68.7KHz, a little over 6mvpp.

Manage to find a GW Instek distributor here and he is bringing me the 2000E to try to see my signal with digital filter.

[StillTrying]

There can't be any 4 mVpp 4MHz sine wave in that last scope image, you'd see it as a thick trace or aliasing.

[ultrasmurf]

Yup, last pic is just noise picked up at test point. The signal path to the test point is removed physically just to try to see if I could actually make it cleaner. Why I never do this before ? Because my CRO can display my signal by just twisting the trigger and hold knob... so the noise dont really bother me.

[ultrasmurf]

So, I just demo'ed the GW Instek 1072B. Very useful bandpass filter. Showed me my signal no problem...  I'm ordering the 1054B, just to have 4 channel, and 50MHz is plentiful.

The pic showed the signal still dance left to right a little bit, so I guess the trigger is still seeing the unfiltered signal. The waveform update a little bit slower (I guess due to the filtering) but responsive enough (much more reponsive than using average filter) that when I do my tuning it is pretty much realtime feedback on the screen. BTW not exactly the same test as to the same device where I started this thread, as I am disassembling that at the moment, and the available one is a 2MHz at 1.5mVpp. Same noise level, same placement on my table. Will probably run more test when the unit arrived if anyone interested. But I guess this is pretty specific to my need...

So thanks so much for the recommendation. I am sure I will be sitting alone in the office one night and thinking about why I did not choose the pretty color from siglent... and come up with some excuse to have that as well... ( I need to see those 5 phase stepper driver waveform to ensure that the motor is turning correctly... hence i need 2x 4 channel oscilloscope.. right )

[Fungus]

So, I just demo'ed the GW Instek 1072B. Very useful bandpass filter. Showed me my signal no problem...  I'm ordering the 1054B, just to have 4 channel, and 50MHz is plentiful.

I'm sure you'll enjoy the well designed user interface as well. 

[gtr]

Hello,

My result in Average mode = 256.

[Keysight DanielBogdanoff]

Probably a little late to the party, but I'd avoid having to use Fast Acq unless absolutely necessary, there are a lot of gotchas that pop up. From our lineup (Keysight) you might also take a look at the 1000 X-Series, they go down to 1 mV/division in hardware so it should handle that noise fairly well and meet your budget & use guidelines:

http://www.keysight.com/en/pcx-2759552/infiniivision-1000-x-series-oscilloscopes?cc=US&lc=eng

I'ts a pretty nice cheap scope, you get the same UI & processor as the much-more-expensive Keysight scopes, but it has a more sensitive front end giving you better noise performance at 1 mV/division.

[BrianH_Tektronix]

I think you're right Daniel, FastAcq is not the right tool to be using here. To be honest if you're looking at a 4mVpp signal, then yes you'll want a scope that can take you down to something small like 1mV/div to 2mV/div in hardware (like the Tek 3 Series MDO or TBS Series). Then you'll want to use a bandwidth filter with High Res mode (if its single shot) and if the signal is repetitive, you might just want to do a bandwidth filter with averaging. Averaging sounds like the right scope feature and its found in almost any scope on the market. All these features reduce noise and increase your probability of seeing a small signal as you are wanting.

The second thing to remember is probing. You'll want to reduce probe attention (don't use the standard 10x probes), but rather check out something like a TPP0502 which has 2x attention. This provides a larger signal into the ADC and shows less noise that would have been amplified from the scope front end.

Good luck @ultrasmurf  finding your next scope and hope its from Tek



Cheers,
Brian