New DS1054z jitter problem - Page 1
Forum section: electronics / testgear

author: droffsite
author_rank: Newbie
timestamp: July 08, 2016, 02:08:43 am
content: Good evening, everyone. I've just today acquired a DS1054z, firmware 00.04.03.SP2, board rev 0.1.1. I calibrated the probes and figured I'd try out something simple.<disclaimer>I'm new to the world of scopes. I'm working on a physics degree (25 years after my first degree) and wanted to get my hands dirtier than the labs will allow.</disclaimer>I fired up a function generator producing a 16 kHz sine wave. I got the waveform you see in the attachment ending in 2. At 1 kHz it looked like the attachment ending in 4. Alternatively (not sure what the difference was), the wave would dance up and down, left to right, in a wave.In the course of trying different probes and looking through all the menus, I happened to touch the trigger out/pass fail port on the back. I then got the image in the attachment ending in 3: the steady waveform I was expecting. As soon as I removed my finger, the jitter started back up.Is there some calibration I've missed? Do I need a terminator on the trigger connector?Thoughts?

author: ataradov
author_rank: Super Contributor
timestamp: July 08, 2016, 02:58:02 am
content: Looks like some grounding issue. Can you describe your setup in more details? What function gen? How it is connected to the scope?

author: alsetalokin4017
author_rank: Super Contributor
timestamp: July 08, 2016, 03:00:34 am
content: This looks like a grounding issue to me. The "dancing up and down" sounds like it could be a typical mains frequency pickup superimposed on the signal from the FG, which goes away when you touched the BNC on the back panel. Does it also go away when you touch one of the front panel BNC channel input connectors? All the BNC shields are, or should be, connected internally together and to the chassis ground, which in turn is, or should be, connected to the mains plug ground pin.No, you should not need a terminator on the trigger/passfail output connector.What kind of FG are you using, and how are you connecting the scope probe to the FG?

author: droffsite
author_rank: Newbie
timestamp: July 08, 2016, 03:12:54 am
content: The setup is pretty basic, as I'm just getting started.The generator in this case is f Generator, an IOS app running on an iPad. I tried both with the iPad plugged in and just on battery power.I have a mini plug to mini plug cable in the headphone jack of the iPad. I clamped the ground to the lowest ring and the probe to the tip.Touching the connectors on the front also stopped it (thought I'd tried that earlier; apparently I hadn't).Bad power cable?Sent from my iPhone using Tapatalk

author: droffsite
author_rank: Newbie
timestamp: July 08, 2016, 03:42:29 am
content: Or maybe a bad audio cable. Put a different cable in and all looks great.Hell of a way to introduce myself...Very much appreciate the quick replies!

author: ataradov
author_rank: Super Contributor
timestamp: July 08, 2016, 03:52:24 am
content: Quote from: droffsite on July 08, 2016, 03:42:29 amStuff happens.To diagnose issues like this, change your time base to the point where you can see 2-3 periods of 60 Hz (or 50 Hz). In this case you will see your signal superimposed on top of that 60 Hz. That's why you see this difference in amplitude between different trigger events.