Author Topic: Scope channel Noise difference?  (Read 18180 times)

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Offline WmackyTopic starter

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Scope channel Noise difference?
« on: March 21, 2015, 08:05:51 am »
Is there an acceptable limit for a noise difference between channels on a brand new 2 channel scope, and with nothing connected to the inputs?  Does it matter?
 

Offline rs20

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Re: Scope channel Noise difference?
« Reply #1 on: March 21, 2015, 08:22:34 am »
Check the noise relative to the specs of the scope, rather than between channels. If the noisier channel is out of spec, then there's a confirmed problem. Otherwise, your scope is in spec. I don't particularly see a reason for defining acceptable limits on noise equality between channels.

Having said all that, the channels are supposed to be identical circuitry so it is some sort of cause for concern. Although, at the same time, I'm always skeptical of these people who test the noise floor of their scopes by leaving the inputs unconnected. Unconnected means open circuit, high impedance, extreme noise sensitivity. It's entirely possible that the noisier channel just has a noise source physically closer to it on the PCB, but the problem goes away once a reasonably low-impedance signal is attached. Of course, 10x probes hardly affect the impedance of the node, but still. It'd make more sense to me to connect a terminator to the input to test noise floor, and would at least help with diagnosing your issue.
 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #2 on: March 21, 2015, 09:16:07 am »
I just found the difference odd, as my upstanding is both channel are built the same. That, and the fact that all the Youtube videos I've watched for this scope seems to indicate identical noise levels in the all that showed unconnected inputs. I switched in the scope 50 Ohm input with no difference. Channel 1 seems consistently noisier than channel 2.
 

Online T3sl4co1l

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Re: Scope channel Noise difference?
« Reply #3 on: March 21, 2015, 09:40:01 am »
Measurements?  Model?
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Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #4 on: March 21, 2015, 09:54:36 am »
 

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Re: Scope channel Noise difference?
« Reply #5 on: March 21, 2015, 10:05:14 am »
Measurements?
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Offline JohnnyBerg

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Re: Scope channel Noise difference?
« Reply #6 on: March 21, 2015, 10:05:44 am »
and with nothing connected to the inputs?

I thinks you should put both inputs to ground, with no probes attached. Noise injection could be different, depending on the location, and how the scope is placed on the bench.
 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #7 on: March 21, 2015, 10:14:21 am »
and with nothing connected to the inputs?

I thinks you should put both inputs to ground, with no probes attached. Noise injection could be different, depending on the location, and how the scope is placed on the bench.

How best to achieve this?
 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #8 on: March 21, 2015, 10:15:10 am »
Measurements?
Which measurements?    Kinda new to DSO's

Do you mean total noise levels?  At full 300 MHz bandwidth?
If so, and by visual guesstimation      Channel 1  -  about 5.5mv    Channel 2 -  6 mv
« Last Edit: March 21, 2015, 10:22:34 am by Wmacky »
 

Offline dom0

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Re: Scope channel Noise difference?
« Reply #9 on: March 21, 2015, 10:21:11 am »
That thing probably has measurement functions. For now peak to peak voltage and RMS voltage are of interest. Also check whether the noise is always different or only on the lowest vertical setting.


Some compact scopes (the typical Hameg or Tek 2xxx series design with the tube left and the controls and inputs to the right) had issues with the channel closer to the CRO being a bit noisier and the like. Given that many displays radiate EMI like there were no tomorrow I wouldn't be surprised if some DSOs have similar issues.
« Last Edit: March 21, 2015, 10:23:08 am by dom0 »
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Offline JohnnyBerg

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Re: Scope channel Noise difference?
« Reply #10 on: March 21, 2015, 10:27:58 am »
and with nothing connected to the inputs?

I thinks you should put both inputs to ground, with no probes attached. Noise injection could be different, depending on the location, and how the scope is placed on the bench.

How best to achieve this?

Huh? Just select GND as the input coupling on the scope.
 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #11 on: March 21, 2015, 10:31:39 am »
From a single shot:

Channel 1

VRMS     620uV
VPP v 1.8 mV


Channel 2

VRMS   542uV
Vpp    1.56 mV





« Last Edit: March 21, 2015, 10:35:00 am by Wmacky »
 

Offline JohnnyBerg

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Re: Scope channel Noise difference?
« Reply #12 on: March 21, 2015, 10:35:43 am »
There is not that much difference between the channels.

But I find the noise rather high. Can you show a picture on how you measure this?
 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #13 on: March 21, 2015, 10:36:54 am »
and with nothing connected to the inputs?

I thinks you should put both inputs to ground, with no probes attached. Noise injection could be different, depending on the location, and how the scope is placed on the bench.

How best to achieve this?

Huh? Just select GND as the input coupling on the scope.

No "ground" Option under input.   Ground coupling only.....
 

Offline dom0

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Re: Scope channel Noise difference?
« Reply #14 on: March 21, 2015, 10:38:29 am »
Ground coupling is precisely that. It connects (couples) the input to ground.
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Offline JohnnyBerg

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Re: Scope channel Noise difference?
« Reply #15 on: March 21, 2015, 10:42:32 am »

Huh? Just select GND as the input coupling on the scope.

No "ground" Option under input.   Ground coupling only.....

 :-//

YT on scope basics?
 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #16 on: March 21, 2015, 10:48:21 am »
Ground coupling is precisely that. It connects (couples) the input to ground.

In that case, no noise with input to ground, All measurements =0
 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #17 on: March 21, 2015, 10:49:21 am »

Huh? Just select GND as the input coupling on the scope.

No "ground" Option under input.   Ground coupling only.....

 :-//

YT on scope basics?
  Thanks, I'll get right on that.
 

Offline rs20

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Re: Scope channel Noise difference?
« Reply #18 on: March 21, 2015, 10:58:08 am »
I'm not sure GND coupling is a useful option for Rigol scopes; on my Rigol DS2202 GND coupling is quite clearly just a digital zero, there's no noise at all.
 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #19 on: March 21, 2015, 11:12:55 am »
I'm not sure GND coupling is a useful option for Rigol scopes; on my Rigol DS2202 GND coupling is quite clearly just a digital zero, there's no noise at all.

Which led to my confusion. Your correct, ground coupling appeared to kill the internal noise completely, and really didn't offer anything. I wasn't sure I was understanding Johnnyberg's request completely.



Here's a pic.


« Last Edit: March 21, 2015, 11:24:44 am by Wmacky »
 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #20 on: March 21, 2015, 11:23:56 am »
Lots of variability between these single shot numbers. The pics I'm posting are with DC coupling. The very first numbers were with AC coupling.  Bigger channel difference with DC. Notice the central spike on channel 1 that's always there. It moves with the  horizontal position control, and only exists on DC coupling?

Another
 

Offline JohnnyBerg

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Re: Scope channel Noise difference?
« Reply #21 on: March 21, 2015, 11:24:04 am »
And what is on the inputs?
Open scope probes are antenna's ;)

I have some of these, to "seal" the inputs.

 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #22 on: March 21, 2015, 11:26:59 am »
And what is on the inputs?
Open scope probes are antenna's ;)

I have some of these, to "seal" the inputs.



Nothing connected. I have no terminators.  :(        I'm afraid my "return" window would close before some could arrive.................................
 

Offline dom0

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Re: Scope channel Noise difference?
« Reply #23 on: March 21, 2015, 11:27:22 am »
Yeah, stick a terminator in or short the input out with a small piece of wire from the center conductor directly to the shell of the BNC.


Interesting that Rigol tries to cheat with GND coupling. How dumb do they think their customers are?
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Offline JohnnyBerg

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Re: Scope channel Noise difference?
« Reply #24 on: March 21, 2015, 11:31:01 am »
Interesting that Rigol tries to cheat with GND coupling. How dumb do they think their customers are?

I thought it was a assumption? Did you look look at the schematics?
 

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Re: Scope channel Noise difference?
« Reply #25 on: March 21, 2015, 11:39:28 am »
What happens if you keep pressing the one-shot button?

Create a table:
Trial ChA ChB
1   5.5mV 6mV
2   ?      ?
etc.

You're doing noise, so you have to do statistics!  If there is a clear trend between these data series, then one may well be noisier.  So far, your two data points ("looks like 5.5, 6" and single shot "1.8, 1.56") aren't suggesting much of a trend. :)

The scope tells you it's reading some amount of mV, but that's a convenience only; ultimately, it's only measuring what appears at the sampling circuit.  Which is the sum of internal noise (the analog to digital converter isn't perfect, and makes mistakes), buffering and amplification (random thermal noise in the circuits, amplified by a lot because the converter itself probably senses ~1V signals), and what's actually at the input connector itself (which isn't much compared to the rest, even if terminated in 50 ohms and nothing else).  And when it performs a sample operation, it simply pulls that number out of the random cloud: the expected value of a given sample is simply the amplitude of the noise, period.  So from any given series of samples, it's simply going to be... random, no matter how fast or slow you sample at.

The noise amplitude depends on bandwidth, however.  If you have the scope configured for 100MHz (or more?) bandwidth, and the noise spectrum is flat, then reducing it to 20MHz BW will yield sqrt(100/20) ~= 2.2 times less noise.  The reduction is even more significant if you set an even lower bandwidth: there are probably settings for digital filtering (as a percentage of displayed rate), or "high res mode", or averaging mode (with averaging, the expected reduction for un-triggered components is sqrt(1/N), so for N=100, the noise goes down by 10x).

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Offline dom0

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Re: Scope channel Noise difference?
« Reply #26 on: March 21, 2015, 11:45:11 am »
Interesting that Rigol tries to cheat with GND coupling. How dumb do they think their customers are?

I thought it was a assumption? Did you look look at the schematics?

You'd have to go a faaaaaaaar way to create a system with 300 MHz bandwidth and that sensitivity that has less than 1/2 LSB noise, which is the only way you'd see only zero codes on the scope. Or they zero them digitally.
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Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #27 on: March 21, 2015, 11:47:15 am »
Standby  - Statistical measurements coming up in 5 minutes!
 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #28 on: March 21, 2015, 11:53:23 am »
OK here's a 2 minute statical measurement.  ( I'm learning alot tonight about using this scope!!!! >:D ;))

Look at those averaged numbers.  (bottom left)  This newbie thinks that not good.  :P :-[

I tried shorting the inputs, but I need terminators, the wire isn't working so well. I've moved the unit all around the room, and still channel 1 is higher.   I'm pretty new to this stuff, but my gut tells me it's internal noise.........  What to do................
« Last Edit: March 21, 2015, 11:57:30 am by Wmacky »
 

Offline rs20

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Re: Scope channel Noise difference?
« Reply #29 on: March 21, 2015, 12:26:21 pm »
All this fuss over a 300uV difference? Geez, I thought you were talking about a significant difference. <loses all interest in this thread>
 

Offline cyr

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Re: Scope channel Noise difference?
« Reply #30 on: March 21, 2015, 12:35:24 pm »
Lots of variability between these single shot numbers. The pics I'm posting are with DC coupling. The very first numbers were with AC coupling.  Bigger channel difference with DC. Notice the central spike on channel 1 that's always there. It moves with the  horizontal position control, and only exists on DC coupling?

Another

That spike is probably there because you are triggering on it. That may explain part of the difference you are seeing as well, check what happens if you trigger on channel 2 instead or move the trigger level way above the noise so the scope runs untriggered.

In any case, nothing worth worrying about.
 

Online Fungus

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Re: Scope channel Noise difference?
« Reply #31 on: March 21, 2015, 12:36:18 pm »
Try moving it around the room.

Electrical noise depends on all sorts of things, including position/orientation.

But really ... unless the difference between the channels is huge then you're most likely worrying over nothing - the channel with more 'noise' might actually be the best as it has more bandwidth!   :-+

Some noise is normal - see Dave's video:

Edit: Then again, Rigols have shielding so the noise is probably coming from inside. One channel's input circuitry is probably closer to some oscillator than the other one.

« Last Edit: March 21, 2015, 02:33:48 pm by Fungus »
 

Offline tautech

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Re: Scope channel Noise difference?
« Reply #32 on: March 21, 2015, 12:38:43 pm »
All this fuss over a 300uV difference? Geez, I thought you were talking about a significant difference. <loses all interest in this thread>
+1
This level if measurement will rarely be used in practice and the noise you see could also be from your enviroment.
Try another location.

Have you watched these?
http://www.eevblog.com/2014/04/10/eevblog-601-why-digital-oscilloscopes-appear-noisy/

http://www.eevblog.com/2014/04/27/eevblog-610-why-digital-scopes-appear-noisy-part-2/


I might add if you had a $20K scope you might have something to grizzle about.

DSO's show all sorts of noise unterminated, especially when set to Peak detect.

If it is within Manufacturers specs....it is what it is.
That is all that you should be concerned with.
« Last Edit: March 21, 2015, 12:42:47 pm by tautech »
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Offline ebastler

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Re: Scope channel Noise difference?
« Reply #33 on: March 21, 2015, 12:39:04 pm »
Interesting that Rigol tries to cheat with GND coupling. How dumb do they think their customers are?
On my DS1054Z, there clearly is some remaining "real world" noise when the input mode is set to GND. No cheating there. Maybe someone could verify the statement that GND produces a flat line on the DS2000 scopes?
 

Offline JohnnyBerg

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Re: Scope channel Noise difference?
« Reply #34 on: March 21, 2015, 12:43:25 pm »
On my DS1054Z, there clearly is some remaining "real world" noise when the input mode is set to GND. No cheating there.

Here to. Depending on the timebase setting: 80µV pp @ 2µS/div and  440µV pp @ 200nS/div
 

Offline tautech

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Re: Scope channel Noise difference?
« Reply #35 on: March 21, 2015, 01:04:32 pm »
Interesting that Rigol tries to cheat with GND coupling. How dumb do they think their customers are?
On my DS1054Z, there clearly is some remaining "real world" noise when the input mode is set to GND. No cheating there. Maybe someone could verify the statement that GND produces a flat line on the DS2000 scopes?
Normal.
They are powered with a SMPS, they have a SMPS for the display LCD backlight.

All the shielding in the world can't prevent some of this EMI from entering the scope circuitry in some small way.
How you use the scope and manage known EMI is important.
So noise originating from SMPS within could be in the 30-50 KHz range could be from the PSU.
On the main PCB there will also be a number of oscillators ranging from 5 to maybe 100 MHz.

It's noise and only noise, understand that, live with it and manage it.  ;)
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Offline ebastler

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Re: Scope channel Noise difference?
« Reply #36 on: March 21, 2015, 01:57:53 pm »
Interesting that Rigol tries to cheat with GND coupling. How dumb do they think their customers are?
On my DS1054Z, there clearly is some remaining "real world" noise when the input mode is set to GND. No cheating there. Maybe someone could verify the statement that GND produces a flat line on the DS2000 scopes?
Normal. [...]
It's noise and only noise, understand that, live with it and manage it.  ;)

Sure, we are on the same page here. I do not expect a perfect "flat line" Quite to the contrary, what I said was that I find it re-assuring to see some noise. It indicates that the scope actually GNDs its analog input and keeps the AD conversion active, rather than "simulating" a grounded input by pushing out digital zeros.
 

Offline dom0

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Re: Scope channel Noise difference?
« Reply #37 on: March 21, 2015, 02:51:17 pm »
Btw. I didn't find any specification from Rigol regarding noise of these scopes. They saw "low noise bla bla", but no numbers. (Batronix has the data sheets, rigolna.com wants personal data, nayyy)
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Online Fungus

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Re: Scope channel Noise difference?
« Reply #38 on: March 21, 2015, 03:02:27 pm »
Btw. I didn't find any specification from Rigol regarding noise of these scopes. They saw "low noise bla bla", but no numbers.

That's because it depends on an awful lot of factors which aren't under Rigol's control.

OTOH Rigol did give you an 'analog display' function which can do a decent job of showing the true signal (see Dave's "why digital 'scopes appear noisy" video for explanation).

 

Offline dom0

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Re: Scope channel Noise difference?
« Reply #39 on: March 21, 2015, 03:06:25 pm »
Btw. I didn't find any specification from Rigol regarding noise of these scopes. They saw "low noise bla bla", but no numbers.

That's because it depends on an awful lot of factors which aren't under Rigol's control.

That's the case with many specifications. It's not like you can't specify it, they just didn't.

OTOH Rigol did give you an 'analog display' function which can do a decent job of showing the true signal (see Dave's "why digital 'scopes appear noisy" video for explanation).

Well... I have my issues with the nomenclature of a "true" signal, but I get your point. And indeed, averaging is a useful feature to extract a repetitive waveform with high uncorrelated (noise) contents. But then again I mostly care for how the waveform looks on the wire, with all the nice noise on top.
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Offline dom0

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Re: Scope channel Noise difference?
« Reply #40 on: March 21, 2015, 03:41:23 pm »
w/o saying anything about bandwidth all noise figures are meaningless. Also it's not only about the converter and it's q. and excess noise but also about the input PGA.
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Offline Rupunzell

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Re: Scope channel Noise difference?
« Reply #41 on: March 21, 2015, 04:52:09 pm »
Depends on what one is working on. For most of the common low speed digital stuff and many electronic things in general, that difference of 300 uV noise between channels might not make any difference at all. Still, that difference in noise between channels is indicative of the design, production and parts used. If the designers were very careful and highly skilled with high quality parts used and equally high standards of production, both channels would have identical performance say within 5% or better. If moving the instrument around alter's it response external fields, there are internal shielding and related sensitivity problems that should have been addressed during it's design. If the instrument or other electronic device is dumping HF energy into it's environment, it can affect the performance of other electronic devices near it.

For the Analog folks doing low noise high performance design (less than one nanovolt/root-Hz at the input), that 300uV difference between channels would make that instrument mostly useless. The Tek 1A7A, 7A22 plug-in have 10uV per/division sensitivity and the noise is much less than one division. Granted these have a 1Mhz BW, yet if one puts two 7A22s into a Tek 7000 series mainframe, their noise displayed would be nearly equal, certainly within 5-10% of each other if they meet spec.

Another example would be the Tek 7A13, 100 Mhz differential input-voltage comparator plug-in, the displayed noise spec is 400uV max.


Bernice




It's noise and only noise, understand that, live with it and manage it.  ;)
 

Online Fungus

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Re: Scope channel Noise difference?
« Reply #42 on: March 21, 2015, 05:27:29 pm »
w/o saying anything about bandwidth all noise figures are meaningless. Also it's not only about the converter and it's q. and excess noise but also about the input PGA.

It's also a lot about the probes plus whatever it is you're connecting them to at the time. I'd say the ringing and other distortions caused by the probes is far more important than a bit of noise in the uV range.
 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #43 on: March 21, 2015, 06:34:24 pm »
I have to say, I'm not feeling that I yet have a definitive answer as to if I have a problem or not.

The issue is that I have 1 day in my easy return window to determine if this scope is working normally or not.  The answers seem to have ranged from, the channels should match to it's doesn't matter, and  it doesn't matter but the overall noise level is too high.  As mention there are no noise stats for the scope The only reference I have is a video by Dave testing a 2202, and the noise appears well matched between  channels, and he commented that the unit had low noise.  This with no terminators and which I will nopt be able to obtain until after my window closes.

Some mentioned bandwidth.  I did mention earlier that the bandwidth is 300 MHZ, and the pics, stats are from the max BW.

Below are 2 additional pics limited to 100 MHZ.  And 20 Mhz respectively.

As you can see, the noise level drops as expected, but the 1st channel consistently reads high.



« Last Edit: March 22, 2015, 07:45:31 pm by Wmacky »
 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #44 on: March 21, 2015, 06:39:31 pm »
So I guess it comes down to this.

Do I just enjoy the new scope being assured it's working just as it should, or do I call the vendor Monday morning and tell them there is a problem. So far the responses to to lean both ways?  I'm not sure what other data I can offer? Ideas?

EDIT:   I was able to properly short the input to ground using a small wire.    I also moved the scope to different locations. No difference seen.   What I'm seeing appears internal?


Anyone out there with a 2072, 2202, or a 2302 seeing the same noise discrepancy between channels, or noise levels?   Perhaps using  band limiting to level the field between the different BW models?
« Last Edit: March 21, 2015, 06:56:37 pm by Wmacky »
 

Offline wraper

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Re: Scope channel Noise difference?
« Reply #45 on: March 21, 2015, 06:54:03 pm »
I have to say, I'm not feeling that I yet have a definitive answer as to if I have a problem or not.

The issue is that I have 1 day in my easy return window to determine if this scope is working normally or not.  The answers seem to have ranged from, the channels should match to it's doesn't matter, and  it doesn't matter but the overall noise level is too high.  As mention there are no noise stats for the scope The only reference I have is a video by Dave testing a 2202, and the noise appears well matched between  channels, and he commented that the unit had low noise.  This with no terminators and which I will nopt be able to obtain until after my window closes.

Some mentioned bandwidth.  I did mention earlier that the bandwidth is 300 MHZ, and the pics, stats are from the max MW.

Below are 2 additional pics limited to 100 MHZ.  And 20 Mhz respectively.

As you can see, the noise level drops as expected, but the 1st channel consistently reads high.
So did you try to set channel 2 as trigger source as others suggested? I don't see that you mentioned doing this.
BTW on my 200 MHz unlocked DS2072 which have almost the same front end noise is higher than yours.
 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #46 on: March 21, 2015, 06:57:44 pm »
I did change the trigger.  The spike went away, but all  channel noise level difference remained.

Also mine is actually a 2072A unlocked to 300 Mhz.  Interesting that your noise is higher. How matched are the channels regarding noise?   The channel difference was of more concern than overall noise, but I glad to see the total level is not out of the norm for the scope. That's good!

Guy's I know 300uV isn't much, My concern was just that one channel consistently reading different could indicate a issue causing other concerns?  If all is well then great. I just don't have the experience to make the call, which is why I'm bending the ear of my well experienced forum mates!  8) :D
« Last Edit: March 21, 2015, 07:17:32 pm by Wmacky »
 

Offline dom0

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Re: Scope channel Noise difference?
« Reply #47 on: March 21, 2015, 07:33:40 pm »
For LF you can easily test if the channels match well with a Y-like cable.
(For RF you'd want a power splitter to do that.)
,
 

Online Fungus

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Re: Scope channel Noise difference?
« Reply #48 on: March 21, 2015, 08:02:08 pm »
Have you done a calibration? Maybe it will go away...   :-//

 

Offline OldNeurons

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Re: Scope channel Noise difference?
« Reply #49 on: March 21, 2015, 09:07:37 pm »
So I guess it comes down to this.

Do I just enjoy the new scope being assured it's working just as it should, or do I call the vendor Monday morning and tell them there is a problem. So far the responses to to lean both ways?  I'm not sure what other data I can offer? Ideas?

EDIT:   I was able to properly short the input to ground using a small wire.    I also moved the scope to different locations. No difference seen.   What I'm seeing appears internal?


Anyone out there with a 2072, 2202, or a 2302 seeing the same noise discrepancy between channels, or noise levels?   Perhaps using  band limiting to level the field between the different BW models?

Here are my results at 500µV and 1mV, 300 / 100 / 20 MHz bandwith.
Rigol DS2102A Unlocked (all options, 300MHz)
Hope this will help you.
My scope also shows a bit more noise on CH 1 but I really don't care.

« Last Edit: March 21, 2015, 10:23:49 pm by OldNeurons »
 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #50 on: March 22, 2015, 02:58:51 am »
That was very helpful.  Thanks for taking the time to do that!  :-+

I really just wanted to make sure this brand new scope was not to far from the norm for these units. This last post gives me some comfort.


As to calibration. Yes, that was tried early on. No dice!
« Last Edit: March 22, 2015, 03:10:57 am by Wmacky »
 

Offline miguelvp

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Re: Scope channel Noise difference?
« Reply #51 on: March 23, 2015, 12:35:56 am »
Did you calibrate it after say, 20 minutes? because on boot it takes a while to settle.
Of course when you power it up it will be off but will get to the calibrated state after several minutes.

If you calibrate right after powerup it will tend to drift and be off after being on for a while.

Edit: Still the voltage drift and settle time might annoy some but the purpose for the scope is about timing accuracy.
« Last Edit: March 23, 2015, 12:37:35 am by miguelvp »
 

Offline tautech

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Re: Scope channel Noise difference?
« Reply #52 on: March 23, 2015, 02:39:48 am »
Did you calibrate it after say, 20 minutes? because on boot it takes a while to settle.
Of course when you power it up it will be off but will get to the calibrated state after several minutes.

If you calibrate right after powerup it will tend to drift and be off after being on for a while.

Edit: Still the voltage drift and settle time might annoy some but the purpose for the scope is about timing accuracy.
Yes, but since the very first oscilloscope settling time has been well known.
Componentry takes time to fully reach a temperature where results are consistant.

Most if not all Service manuals specify a mimimun time powered on before calibration adjustments are made.
A similar time is usually also stated in the manual before a "Self Cal" is done.

All this is well known by experienced users but catches newbies out.
Avid Rabid Hobbyist.
Some stuff seen @ Siglent HQ cannot be shared.
 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #53 on: March 23, 2015, 03:08:38 am »
Yep, I calibrated dead cold.  :P   I just did it again after a warm up. Live and learn.  Unfortunately no change.

BUT!   I did somewhat resolve my issue.  I downgraded the scope to 200 MHZ.  At that bandwidth the channel noise difference Vpp AVERAGED is only 60uV!  And. it looks prettier on the screen @ 500uV P/D.


YeaH, I know.  I haven't done anything but knock off a grand of value from the scope. But, it doesn't piss me off as much now when I look at it.  Perhaps I should forget about it? Unless someone thinks that's a mistake and it's with returning. I PMed Dave and hope for his comment. I'd love to learn if he gives it a thumbs up or swift kick!
« Last Edit: March 23, 2015, 03:23:40 am by Wmacky »
 

Offline rs20

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Re: Scope channel Noise difference?
« Reply #54 on: March 23, 2015, 03:22:42 am »
BUT!   I did somewhat resolve my issue.  I downgraded the scope to 200 MHZ.  At that bandwidth the channel noise difference Vpp AVERAGED is only 22uV!  And. it looks prettier on the screen @ 500uV P/D.

Reducing bandwidth reduces peak-to-peak/RMS noise, because you're filtering away some of the noise. This isn't surprising, and Dave's done a video about it (under the guise of explaining why digital scopes appear noisier). The scope also has hi-res and averaging acquisition modes which will reduce the noise a whole lot more, without compromising bandwidth. How often do you plan to use the scope at the most sensitive voltage setting?

YeaH, I know.  I haven't done anything but knock off a grand of value from the scope. But, it doesn't piss me off as much now when I look at it.

All I can say is: an oscilloscope is a tool, not a work of art. What you've written above is profoundly irrational.
 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #55 on: March 23, 2015, 03:28:12 am »
BUT!   I did somewhat resolve my issue.  I downgraded the scope to 200 MHZ.  At that bandwidth the channel noise difference Vpp AVERAGED is only 22uV!  And. it looks prettier on the screen @ 500uV P/D.

Reducing bandwidth reduces peak-to-peak/RMS noise, because you're filtering away some of the noise. This isn't surprising, and Dave's done a video about it (under the guise of explaining why digital scopes appear noisier). The scope also has hi-res and averaging acquisition modes which will reduce the noise a whole lot more, without compromising bandwidth. How often do you plan to use the scope at the most sensitive voltage setting?

YeaH, I know.  I haven't done anything but knock off a grand of value from the scope. But, it doesn't piss me off as much now when I look at it.

All I can say is: an oscilloscope is a tool, not a work of art. What you've written above is profoundly irrational.

I was trying to be humorous I guess. So is it your suggestion that the scope should stay?  Nobody has really stated what they would do in my shoes. Again, I'm rather new to this, and appreciate the experience of others more familiar......
 

Offline rs20

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Re: Scope channel Noise difference?
« Reply #56 on: March 23, 2015, 03:37:04 am »
I was trying to be humorous I guess. So is it your suggestion that the scope should stay?  Nobody has really stated what they would do in my shoes. Again, I'm rather new to this, and appreciate the experience of others more familiar......
My 2c: when I look at those maximum-vertical-zoom, non-bandwidth-limited, no-averaging, no-hi-res screenshots, they both look terrible. Superimpose a signal of interest on top of that, and it's going to be a horrible experience trying to sort the signal from the noise. This isn't a fault with the scope, you've just put it in the worst case position. If you look at how the noise is 1.5mV or whatever at 300 MHz, that's extraordinary performance for the price point (maybe, I dunno). Set it back to 1V/div, and it'll look perfect.

What you're doing is taking a race car, driving it around an oily hairpin bend at 300 miles per hour and complaining that the tyres have slightly different lack of grip while you smash into the railings. Turn on averaging or hi res, orset it to 1 V/div, and forget about this "problem". Is my very long 2c.

If your scope has significantly (2x) worse noise than another copy of the same model, then that's a different story.
 

Offline JohnnyBerg

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Re: Scope channel Noise difference?
« Reply #57 on: March 23, 2015, 07:48:16 am »
So is it your suggestion that the scope should stay?  Nobody has really stated what they would do in my shoes. Again, I'm rather new to this, and appreciate the experience of others more familiar......

My advise would be to return the scope. You clearly do not know how to operate it, and what its for. What use is a tool, if you do not now what to do with it?

Why did you buy it in the first place, and why 300 MHz? I guess just because it was shinny. You obviously have no idea what to do with that.
 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #58 on: March 23, 2015, 11:43:27 am »
So is it your suggestion that the scope should stay?  Nobody has really stated what they would do in my shoes. Again, I'm rather new to this, and appreciate the experience of others more familiar......

My advise would be to return the scope. You clearly do not know how to operate it, and what its for. What use is a tool, if you do not now what to do with it?

Why did you buy it in the first place, and why 300 MHz? I guess just because it was shinny. You obviously have no idea what to do with that.

Thanks for the smug comment, ( not the first),  and the discouragement of someone that wants to learn. I hope this was able to provide you with a superiority fix.

"Why did you buy it in the first place"          Because I enjoy building Vacuum tube audio amps, and would like to learn to use a Oscilloscope to troubleshoot them. I have other interests as well, such as drone assembly, video flown RC aircraft, amateur radio, and general electronic interests. "Shinny" wasn't a reason I used.

I thank everyone else that took the time to comment.
« Last Edit: March 23, 2015, 12:25:20 pm by Wmacky »
 

Offline JohnnyBerg

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Re: Scope channel Noise difference?
« Reply #59 on: March 23, 2015, 12:06:38 pm »
So is it your suggestion that the scope should stay?  Nobody has really stated what they would do in my shoes. Again, I'm rather new to this, and appreciate the experience of others more familiar......

My advise would be to return the scope. You clearly do not know how to operate it, and what its for. What use is a tool, if you do not now what to do with it?

Why did you buy it in the first place, and why 300 MHz? I guess just because it was shinny. You obviously have no idea what to do with that.

Thanks for the smug comment, ( not the first),  and the discouragement of someone that wants to learn.I hope this was able to provide you with a superiority fix.

I thank everyone else that took the time to comment.

I posted pictures and measurements from my scope. Others told you that the channel difference was insignificant. That there is a relation between bandwidth and noise.

And then you pop that rather silly question, and got a straight, direct answer.

What did you expect to hear?
 

Offline dom0

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Re: Scope channel Noise difference?
« Reply #60 on: March 23, 2015, 12:40:55 pm »
I don't think JohnnyBerg meant to insult you (per se), but rather your choice of tools. Powerful tools usually require equally knowledgeable and powerful users (except for handguns which are safe for everyone) so you're probably better off with a less powerful tool (e.g. less of that noisy bandwidth which you apparently don't need anyway), which is then simpler to use and thus can be put to better use by you. Alternatively, get more knowledgeable about your tools, that works too, but takes time ;-)
,
 

Offline JohnnyBerg

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Re: Scope channel Noise difference?
« Reply #61 on: March 23, 2015, 12:53:24 pm »
I don't think JohnnyBerg meant to insult you (per se),

I certainly do not mean to insult anyone. English is not my native language and I find it difficult to express myself in the right tone  :-[

Quote
but rather your choice of tools. Powerful tools usually require equally knowledgeable and powerful users (except for handguns which are safe for everyone) so you're probably better off with a less powerful tool (e.g. less of that noisy bandwidth which you apparently don't need anyway), which is then simpler to use and thus can be put to better use by you. Alternatively, get more knowledgeable about your tools, that works too, but takes time ;-)

+1
 

Online T3sl4co1l

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Re: Scope channel Noise difference?
« Reply #62 on: March 23, 2015, 01:16:23 pm »
(except for handguns which are safe for everyone)

Spoken like a true 'Murkan!

JK, I don't mean to insult you :P

Tim
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Bringing a project to life?  Send me a message!
 

Offline WmackyTopic starter

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Re: Scope channel Noise difference?
« Reply #63 on: March 23, 2015, 02:05:58 pm »
I don't think JohnnyBerg meant to insult you (per se),

I certainly do not mean to insult anyone. English is not my native language and I find it difficult to express myself in the right tone  :-[

Quote
but rather your choice of tools. Powerful tools usually require equally knowledgeable and powerful users (except for handguns which are safe for everyone) so you're probably better off with a less powerful tool (e.g. less of that noisy bandwidth which you apparently don't need anyway), which is then simpler to use and thus can be put to better use by you. Alternatively, get more knowledgeable about your tools, that works too, but takes time ;-)

+1

Perhaps I overreacted, but the intent of the phrase "I guess just because it was shinny."  seemed clear enough to me?  :-//
« Last Edit: March 23, 2015, 02:24:33 pm by Wmacky »
 


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