Noise on Siglent Function Generator.  Help & Suggestions Please - Page 1
Forum section: electronics / testgear

author: otpowell
author_rank: Regular Contributor
timestamp: December 22, 2015, 04:17:55 pm
content: Anyone have any ideas why I'm getting so much noise from my function generator? Think maybe it's my cables? It's not the scope because there is a calibration square wave on the scope that I compared this signal to and there is no noise on the signal generated by the scope. I was going to disconnect the cable on my generator and hook jumper wires up to see if there's distortion on the signal with out cables. Would that work? The noise appears on other types of signals as well but the noise isn't as bad as on the square wave for some reason. Any other ideas on how to isolate and find the source of the noise?Sent from my iPhone using Tapatalk

author: Unknown
author_rank: Unknown
timestamp: December 22, 2015, 08:02:19 pm
content: Please contact us atinfo@siglent.comWe'll help you troubleshoot this.

author: otpowell
author_rank: Regular Contributor
timestamp: December 22, 2015, 08:11:41 pm
content: Quote from: Siglent America on December 22, 2015, 08:02:19 pmI did indeed send you an e-mail. Actually I sent it toScott initially but has been forwarded to the info box. Thanks.Sent from my iPhone using Tapatalk

author: tautech
author_rank: Super Contributor
timestamp: December 22, 2015, 08:40:33 pm
content: At first glance I'd suspect ringing as you have connection to your DSO via 50 Ohm coax and terminated into 1M and this usually produces unexpected results.If the AWG was set to 50 Ohm output and the coax terminated into 50 Ohm you'd likely get very different results.See this thread:https://www.eevblog.com/forum/testgear/show-us-your-square-wave/

author: rf-loop
author_rank: Super Contributor
timestamp: December 23, 2015, 06:19:20 am
content: SDG 805 or what ever Siglent AWG output impedance is always ~50 ohm in its frequency range, independent of if UI impedance setting between Hi-Z or 50ohm. (or intermadiate values in models and versions where adjustment is available). It do not change output impedance. It change output level display so that it respond this impedance what is connected to AWG.If Owon show no noise problem if connected to its own probe cal output it really do not proof anything. They have same ground and depending connection if there is high amount of common mode noise it can not see. With some "trics" it can see if connection is made so that it translate common mode noise to differential mode noise in oscilloscope input.If your individual Owon have high amount of this noise it still can show very clean signal IF singal is NOT polluted By this common mode noise. (it was old issue after some stupid "EE" overlook how critical is SMPS circuits design including board layout) I know it, I have worked lot of with this special issue in some Owon SDS versions (in history).Worst case is that this noise travel from oscilloscope to inside AWG end stage and it can do "what ever". This noise spectrum is wide in worst case. It may have components up to over 200MHz. Some old Owon what have this worst case issue may be as wide spectrum radio transmitter.If you suspect SDG805 have problem I will recommend that first take real good quality double shielded coaxial what have good quality BNC's in both ends. Take 50ohm feed thru terminator and connect it to oscilloscope input. Then from this to AWG output this coaxial.Better is you find some place where is higher class oscilloscope available and also cable and terminator for scope if it do not itself have.If you see same noise in signal, you can really suspect SDG805 have some kind of fail and you ask warranty service from dealer.I do not know of course if it is at all any isue in this case but just like common note: Do not input RF or any reverse power to AWG output.

author: otpowell
author_rank: Regular Contributor
timestamp: December 23, 2015, 10:33:06 pm
content: Thanks guys, I appreciate the responses. Unfortunately I don't know anyone with a high tech oscilloscope or dual shielded coaxial.This is frustrating. This weekend, my sons Wii U has a problem writing to system memory also. I have good surge projectors and a $300 dollar power filter on my sons Wii (I was young when I bought this, I know power filters aren't worth it). I wonder if something happened like a large surge that hurt my stuff? I guess the only sure way to make sure something is protected from surges is to unplug it.Sent from my iPhone using Tapatalk

author: Wim_L
author_rank: Regular Contributor
timestamp: December 24, 2015, 11:00:30 am
content: I wouldn't expect major problems with ringing here, despite the improper termination. That is only a 100 Hz square wave, so a half period of the waveform lasts 5 ms. Reflections and ringing usually don't last longer than a few nanoseconds on short coax patch cords.Unfortunately, it's going to be tricky to troubleshoot without other equipment. If no other scope is available, perhaps a different signal source can be tested? The SDG 805 seems to have two outputs, see if you can get some kind of signal from th second one perhaps. Other things to check include cables, both the coax (internally broken or intermittent contact? Try using a scope probe instead?) and equipment power cords (a broken ground wire somewhere? Make sure all equipment is plugged in to the same power strip, avoiding long ground loops,...).

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 24, 2015, 11:48:01 am
content: Quote from: Wim_L on December 24, 2015, 11:00:30 amWell, you could always hook up a speaker/headphone and listen to the output, I'm sure a distortion like this would be easy to hear.But then.... I'm almost thinking that somehow there is AM modulation turned on in the FG...

author: Wim_L
author_rank: Regular Contributor
timestamp: December 24, 2015, 12:24:43 pm
content: Quote from: PA0PBZ on December 24, 2015, 11:48:01 amProbably, if it's in an audible frequency range. In that case, it might be best to dial the square wave amplitude down to the minimum, leaving only the noise (if there still is noise when you do that).QuoteIf that thing has AM turned on without clearly showing it on the display, that would be a horrible user interface...

author: dom0
author_rank: Super Contributor
timestamp: December 24, 2015, 12:39:18 pm
content: Quote from: PA0PBZ on December 24, 2015, 11:48:01 amOr some horrid high frequency oscillation in the output amplifier. Maybe a freq compensation cap forgotten / incorrectly picked / defective somewhere?

author: tautech
author_rank: Super Contributor
timestamp: December 24, 2015, 07:55:38 pm
content: Quote from: dom0 on December 24, 2015, 12:39:18 pmThere are several things this noise could be of course, unfortunately the OP has only provide screen shots of the fundamental frequency instead of any at a faster timebase to possibly identify the source of the noise.As rf_loop has pointed out even the LCD of test equipment can be a source of noise and a quick check on another scope could reveal if the AWG has a problem or not.LCD noise is quite common and easily found with a scope probe held close to the instrument like one would do with a near field probe searching for RFI.

author: sarepairman2
author_rank: Frequent Contributor
timestamp: December 24, 2015, 10:09:25 pm
content: e.t. phone home

author: Electro Fan
author_rank: Super Contributor
timestamp: December 24, 2015, 10:37:17 pm
content: Quote from: Wim_L on December 24, 2015, 12:24:43 pmDoes look a little like AM modulated by a square wave....

author: nctnico
author_rank: Super Contributor
timestamp: December 24, 2015, 10:41:56 pm
content: The modulation button isn't lit on the FG so no modulation going on. I think this is a poor ground or signal connection combined with non-grounded mains outlets.

author: Ivan7enych
author_rank: Regular Contributor
timestamp: December 25, 2015, 10:17:52 am
content: Quote from: dom0 on December 24, 2015, 12:39:18 pmI agree.otpowellCan you zoom in by your oscilloscope into this "noise" ? Is it a random noise, or high frequency oscillation?May be there is some radio interference. I hope you don't have some hi power radio transmitter nearby.

author: otpowell
author_rank: Regular Contributor
timestamp: January 02, 2016, 01:10:27 am
content: Quote from: Wim_L on December 24, 2015, 11:00:30 amI actually tried another function generator cable. I noticed it wasn't the cable, switched back to my primary cable. I'm not sure why, but I'm not getting as much distortion now for some reason, nothing that I know of has changed. I have it on peak detect and it displays the most noise on 10M memory length. All devices are plugged in to the same power strip. Do you think this is a normal amount of noise? It looks the most noisy on 10M length and peak detect acquisition mode. The very bottom picture is the square wave on sample acq. mode and 1k length.Sent from my iPhone using Tapatalk

author: otpowell
author_rank: Regular Contributor
timestamp: January 02, 2016, 01:18:12 am
content: Quote from: Wim_L on December 24, 2015, 12:24:43 pmI didn't try the speaker thing yet but I turned it down to as low as the amplitude will go.. 2mVrms. Here's the pics. I have an RMA to send my FG back to Siglent for repair. I just hope that's what the problem really is. Hate to send it and find out that I'm doing something stupid or its a cable or something.Sent from my iPhone using Tapatalk

author: otpowell
author_rank: Regular Contributor
timestamp: January 02, 2016, 01:34:26 am
content: Quote from: Ivan7enych on December 25, 2015, 10:17:52 amIt appears to be high frequency oscillation because there seems to be a repeating pattern to the noise. How much did you want me to zoom in?Frequency is registering at 40.93K. I'm not to fond of the FFT on this thing but here's a picSent from my iPhone using Tapatalk

author: otpowell
author_rank: Regular Contributor
timestamp: January 02, 2016, 01:39:41 am
content: Quote from: tautech on December 24, 2015, 07:55:38 pmWell. I don't remember having the problem before I sent my function generator in for a repair (it wouldn't boot up), then again maybe I just didn't notice before. I doubt it though. I have a Diligent analog discovery USB scope I could check it on that. It's buried somewhere in a box. I guess I'll have to go dig it out.Sent from my iPhone using Tapatalk

author: tautech
author_rank: Super Contributor
timestamp: January 02, 2016, 01:44:10 am
content: OK, so you are using a Coax to clips to scope probes connection that will not be the best for signal integrity, however we see a 700+mV repetitive waveform in the 2nd pic at 10M memory depth of your scope. This is the noise you mention and to investigate further there are further settings you need to change.Leave scope set to 10MEngage AC input couplingIncrease AWG output amplitude to say 1V p-pIncrease scope timebase to measure the frequency of this waveform/noise. (Zoom lots)Second testDirect couple AWG and scope using a BNC to BNC cable, preferably terminated into 50 Ohms.Does noise still exist?I don't at all dismiss your findings and like you we need to find the source of this "noise".Quote from: otpowell on January 02, 2016, 01:39:41 amHmm, I don't recall you mentioning a previous repair.Repaired by whom?

author: otpowell
author_rank: Regular Contributor
timestamp: January 02, 2016, 03:41:09 am
content: The AWG was repaired by a Siglent engineer. I sent him screenshots of the noise and he sent me a return authorization form. I guess I want to make sure it's my function generator before I send it in. I hate not having my AWG for a month or so. I usually need it to complete labs and troubleshoot circuits, etc. I guess I don't need to explain to you guys what I would need it for because you would know better than I. Lol.Thank you for the suggestions, unfortunately I do not have a cable to direct couple. I'll order one of those soon. Can I go bnc to bnc? I saw in a eevblog video he used bnc to female banana on the function generator and I think he used the same but male banana on the scope? I don't remember.I'll run the other test soon engage AC coupling and zoom in to get the freq of the noise. I'll send screen shots.Sent from my iPhone using Tapatalk

author: tautech
author_rank: Super Contributor
timestamp: January 02, 2016, 04:13:12 am
content: Quote from: otpowell on January 02, 2016, 03:41:09 amHas this AWG already been "repaired" for this same noise problem?Frequency hopefully will indicate the source of the noise or at least narrow the possibilities of it's origin.Please post screenshots when you can.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 02, 2016, 04:36:39 am
content: @otpowellIf you don't have BNC patchcords or a 50 ohm terminator, you can just connect your scope probe directly to the female BNC output jacks on the FG. Remove the spring grabber to expose the probe point, and carefully insert the point into the center connector of the BNC output jack on the FG. Clip the probe's ground reference to the bayonet stud on the outer shield of the BNC connector. This will give you the best possible connection between the scope and the FG, in lieu of having actual 50-ohm patch cables with termination.

author: otpowell
author_rank: Regular Contributor
timestamp: January 02, 2016, 05:37:00 pm
content: Quote from: tautech on January 02, 2016, 04:13:12 amNo sir, it was repaired before because all of a sudden, after a year of use, it wouldn't boot up. It would get stuck at the boot screen.Taking screen shots in a few minutes. Standby please.Sent from my iPhone using Tapatalk

author: otpowell
author_rank: Regular Contributor
timestamp: January 02, 2016, 05:42:51 pm
content: Quote from: alsetalokin4017 on January 02, 2016, 04:36:39 amAhh! Great suggestion, thank you sir, I really do appreciate it.Sent from my iPhone using Tapatalk

author: otpowell
author_rank: Regular Contributor
timestamp: January 02, 2016, 06:08:13 pm
content: Quote from: tautech on January 02, 2016, 01:44:10 am

author: tautech
author_rank: Super Contributor
timestamp: January 02, 2016, 07:05:59 pm
content: Great, ~70 KHz, now to try to find where it originates from.Why do I say great? Because to know the frequency will help you find it's source.First thoughts are a noisy SMPS but where?AWG?Bench and surrounds? Other appliances, lights, PC......DSO?Start a process of elimination, suspect anything, list everything, turn things off, unplug things until there can be no other possible culprits. Then take the AWG and DSO to another power socket and check again for noise.One other check first please:Set the AWG for DC output and see if the noise is riding on the DC with your DSO.

author: rf-loop
author_rank: Super Contributor
timestamp: January 02, 2016, 08:01:58 pm
content: Please throw away this probe own black GND wire with alligator.Make GND connection where you see red mark in bottom attached image.How this noise looks now? What you think now. Do you think it is nice to learn what happends there......and after then (perhaps) change this topic subjectHere is one idea how to do itAfter you get image with short GND you know more.

author: otpowell
author_rank: Regular Contributor
timestamp: January 03, 2016, 03:03:34 pm
content: Quote from: rf-loop on January 02, 2016, 08:01:58 pmI'm not sure what you mean. I should throw this probe away because the ground with alligator is no good? I will try your suggestions soon and let you know. Thank you!Sent from my iPhone using Tapatalk

author: otpowell
author_rank: Regular Contributor
timestamp: January 03, 2016, 03:06:16 pm
content: Quote from: tautech on January 02, 2016, 07:05:59 pmWell, I have a SMPS right next to my AWG. Lol ok I'll check that out. Thank you sir.Well! I think I found the source of the noise! It was my laptop! I unplugged my DC supply first and the noise was still there, next I unplugged my laptop and the noise went away! Thanks all, how does my square wave look now? Acceptable and normal amount of noise? One sec, having an issue uploading a pic for some reason.Sent from my iPhone using Tapatalk

author: otpowell
author_rank: Regular Contributor
timestamp: January 03, 2016, 03:30:15 pm
content: 10M memory length.And this pic is taken without my probe direct coupled. The very small noise there is probably a result of my AWG cable.Here's the square wave zoomed in on the noise.Sent from my iPhone using Tapatalk

author: otpowell
author_rank: Regular Contributor
timestamp: January 03, 2016, 03:57:59 pm
content: Well looks like you do know what your talking about. I've traced the noise to my laptop power supply. The noise is not there when the laptop is running on battery.Sent from my iPhone using Tapatalk

author: otpowell
author_rank: Regular Contributor
timestamp: January 03, 2016, 04:13:27 pm
content: Quote from: otpowell on January 03, 2016, 03:57:59 pmSent from my iPhone using Tapatalk

author: tautech
author_rank: Super Contributor
timestamp: January 03, 2016, 05:39:53 pm
content: Quote from: otpowell on January 03, 2016, 03:57:59 pmI'm glad you found it.There still will be EMI at lesser levels from various SMPS on or near your bench, possibly even from your lighting but now you know a little about these things you are better armed to find problems in the future.rf_loop's comment of probe reference (GND) lead length is very valid, they can act as antennae and pick up all manner of interference to confuse a scope user so use of the shortest length reference lead is often desirable.It's just another trick you now know about.

author: otpowell
author_rank: Regular Contributor
timestamp: January 04, 2016, 02:32:55 am
content: Quote from: tautech on January 03, 2016, 05:39:53 pmUnderstood, again thank you so much tautech, and everyone else. I'll add the ground lead length trick to my book of acquired troubleshooting tricks. Most of my fluorescent lighting is far away but at least I know that that the potential exists.Sent from my iPhone using Tapatalk

author: tautech
author_rank: Super Contributor
timestamp: January 04, 2016, 02:36:51 am
content: Quote from: otpowell on January 04, 2016, 02:32:55 amDo contact Steve or Scott and inform them your issue has been resolved.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 04, 2016, 02:43:23 am
content: Many better scope probe kits will come with a "BNC adapter" that fits on the probe and mates with the BNC female jack. Unfortunately there is no "one size fits all" solution, the adapter will be specific to a particular probe dimension.It's the silver thing in the center of this photo:http://thumbs.ebaystatic.com/images/g/5iQAAMXQlbVSGps4/s-l225.jpg