Unfortunately, mine situation is different from what we are expected!
With well charged battery from the worst to best the sequence is: battery (?400mV), battery+ac main(?300mV), ac main (?150mV) - Cheked by Owon Probe after Self Cal procedure and Probe adjustment.
Yes, this is unexpected result.
I have seen before:
(a) battery+ac most bad,
(b) ac without installed battery (battery out) less than a
(c) with battery alone without ac connected, less than b
It need some more investigation. I have some small suspects but too early to say.
But I have some of questions-observations
1) you have different time set, the first was 1ms and now is 500us, normally there is no significant difference but if there is a periodic noise, the time makes the difference.
2) The back cover was closed at the two measurement of noise or they was different? Perhaps, this changed the noise.
3) some times the residues decrease the electricity of components. Personally, I have see some difference to noise after a good bath and very well drying with isopropylic alchool.
4) what you meaning with "Base line noise", from what I see there is no any BW limited or something else.
But please to all member, let us make measurements with same conditions like a protocol.
I copy the directions of rf-loop for comparisons reasons:
Procedure for measurent of GND Noise
----------------------------------------------------
Make a Calibration procedure as manual refer (there is no nessesary if not the temperature variables ±5°C from the initial calibration)
Compensate the probe as manual described.
Change switch probe to 10x and set the same to the Probe Owon Menu (10X).
Connect together the probe tip and the probe aligator ground to Probe Comp GND.
Fix the cable of probe like the attachment photo.
Turn CH2 off.
CH1 to DC, 50mV/Div.
Push Trigger 50%
Set the Acquire Length to 1M and the Acqu. Mode to Peak
Set the Horizontal speed to 100us
Set the measurement to Voltage peak to peak (Vp to Owon) and write the value.
Also, when you capture in peak detect mode, the capture length is always 10M.
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The baseline attachment is the noise when nothing is attached to the BNCs (no probes). Sometimes called baseline because it's supposedly what you start with, independent of ground noise for example.
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Got to go, it's lawn mowing day!
Also, when you capture in peak detect mode, the capture length is always 10M.
Really?
Afaik, not.
Peak mode do not have so much advantage if scope use one channel 1GSa/s or two channel 500MSa/s.
As we know if one channel in use ADC run allways 1x 1GSa/s mode and if 2 channel in use 2x500MSa/s mode. This is independent of time base setting of course. If example selected one channel and 1k memory and 500us/div there read 100kSa/s. But system run 1GSa/s. But it collect to 1k sampling buffer only every 10000th of sample and do not care about these other samples at all. Simplified: In peak mode it is not blind when it drops out these 9999 samples and keep one.. it find highest value and lowest value there.. (becouse still 100kSa/s there is now sequentially ...highest, lowest, highest... after every 10us.)
I do not know how it exactly then build displayed image etc details so there may be some tiny differencies if use 1GSa normal mode or slower but peak mode. In practice not much.
Set 1k memory, 500us/div, peak and display mode dots.
capture just something noisy.
Stop scope. Zoom out ti 1ms/div you see there is 10div
Zoom in to 10us/div. Count sample points... there is 1000
Same but acquire mode normal.
Count sample points, there is 1000.
(nosignal5mVpeak1k.bin.txt) remove .txt
There is 1000 sample points.
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The baseline attachment is the noise when nothing is attached to the BNCs (no probes). Sometimes called baseline because it's supposedly what you start with, independent of ground noise for example.
...
Got to go, it's lawn mowing day!Thanks for explaination TomC, but seems like crazy to me a 10mV base line, normaly should to was to 1mV.
Look, at the last capture that rf-loop upload at the 5mV. The base line noise is 1mV (full BW like yours).
I have a through-hole version also but it doen't use the Z-plate as heatsink for D8.
I have an older through-hole version of the power supply marked PCB-T115-J rev4 and 3.0 adapter.
It was in very first versions and if there is also this totally different front end electromechanical construction then scope is perhaps this very extremely early version.
Hi there guys!
I decided to do some experimenting with ground noise problems, since it seems that I have a particularly "interesting" unit. I have a "thick" part of noise which is around 300 mV peak to peak and some huge spikes which are between 2 V and 3 V (even worse with 150 MHz probes I'm normally using). Their period is around 80 ms. I have an older through-hole version of the power supply marked PCB-T115-J rev4 and 3.0 adapter. From time to time, there will be a huge single peak of 5 V to 6 V as well. One interesting thing is that this PSU is using the "Z-plate" as heatsink for D8.
To get to the source of the noise I connected one probe to the ground pin on the probe compensation connector and moved the other probe around the power supply. From what I can see, most of the peaks seem to be synchronized to the waveform on the coil marked L2. Unfortunately, my power supply does not have coil L3 (which from what I can see if used as a filter) and instead seems to be filtered only with an electrolytic capacitor. I placed two 100 nF 1206 SMD capacitors and two 47 nF 0805 SMD capacitors over the electrolytic. In addition to that, near the power connector there were unpopulated places for ceramic through-hole capacitor and for one electrolytic capacitor on the -7.6 V rail. I placed one 470 µF capacitor and one 100 nF disk ceramic capacitor at the power connector. In addition to that, I placed same set of 4 SMD capacitors in parallel to the electrolytic.
Next, I added two 100 nF 1206 SMD capacitors in parallel with all electrolytic capacitors on the secondary side of the power supply. I also replaced the 1N4007 diodes mentioned few pages back with UF4007, but in my case that made no measurable improvement. My guess is that the reason for that is the large amount of noise that is cancelling all the (minor) improvements I made.
As you can probably guess, I'm poking in the dark here trying to come up with something that would help. My next plan is to get some 1 µF 1206 and 0805 SMD capacitors and place them in parallel with the ones I already have on the -7.6 V rail.
First attached image is how everything looked like with only ferrite on the power cable going from the PSU to the adapter board. Next two images are made after adding the capacitors on the -7.6 V rail and show relationship between the noise peaks and the waveform on L2. Final image is what I get when I use same settings as on the first image. Unfortunately, there seems to be no improvement (in fact I could say it's a bit worse now).
So does anyone have any smart ideas what to try now? I'm starting to run out of ideas and am considering undoing the changes I made since I don't actually have any problems running the scope for my needs. It's just that knowing that the ground noise is there is bugging me.
AndrejaKo, Since you have all that noise around L2, I would check C9 and C11 out of the circuit and replace them if necessary. The amount of noise you have seems more like a malfunction than ground noise. Just a thought!
TomC had you measure before changes what was the threshold for right triggering?
I think that these measures (noise + triggering) there is no way to obtain with the old psu board?
I hadn't test before to my scope the level for right triggering but with very low signals there is no way to examined because noise.
There is some documentation here (it demand login to see the captures) about before and after mods. With noisy gnd and long ground clip 50mVpp square signals there is no way to examined, after mods 1MHz/2mVrms sinus signal is almost perfect with a long gnd clip. But there is no reference about triggering.
It is interesting if other members have some tests before and after and specialy triggering operation.
AndrejaKo, Since you have all that noise around L2, I would check C9, C10 and C11 out of the circuit and replace them if necessary. The amount of noise you have seems more like a malfunction than ground noise. Just a thought!