Oscilloscope input signals have a noise. - Page 1
Forum section: electronics / beginners

author: XMA
author_rank: Contributor
timestamp: March 21, 2018, 10:00:56 pm
content: so as you can see that the scope shows the Sine wave as perfect but now on square wave it gets weird, how do i fix it?

author: DC1MC
author_rank: Super Contributor
timestamp: March 21, 2018, 10:02:49 pm
content: Did you calibrate your probe ?

author: Benta
author_rank: Super Contributor
timestamp: March 21, 2018, 10:13:32 pm
content: ^ this.

author: XMA
author_rank: Contributor
timestamp: March 21, 2018, 10:14:49 pm
content: how do you do that? sry im new to scopes.

author: Benta
author_rank: Super Contributor
timestamp: March 21, 2018, 10:40:05 pm
content: https://www.eevblog.com/forum/beginners/oscilloscope-training-class-(long)/

author: TK
author_rank: Super Contributor
timestamp: March 21, 2018, 10:42:31 pm
content: Quote from: DC1MC on March 21, 2018, 10:02:49 pmI think it is known as probe compensation

author: alsetalokin4017
author_rank: Super Contributor
timestamp: March 21, 2018, 10:57:20 pm
content: Yep, compensation not calibration... but since we don't know where the "square" wave signal is coming from, we can't really tell from here if it is a compensation issue or a signal source issue, or both or neither.XMA, please connect the probe to the scope's compensation signal (or "Probe Adjust") output on the front panel and show the signal from that.

author: XMA
author_rank: Contributor
timestamp: March 21, 2018, 11:12:05 pm
content: Quote from: alsetalokin4017 on March 21, 2018, 10:57:20 pmthe source I was using was my phone using a tone generator app, and on each app, the square wave is always weird. and the other thing is I got a Tektronix 2221 and I don't see anything that is a probe adjust outputs.

author: RobertPS
author_rank: Contributor
timestamp: March 22, 2018, 12:24:18 am
content: Quote from: XMA on March 21, 2018, 11:12:05 pmAbove the focus knob. The procedure is in the manual.

author: XMA
author_rank: Contributor
timestamp: March 22, 2018, 12:43:26 am
content: Quote from: RobertPS on March 22, 2018, 12:24:18 amit says i need to clip it, but how it's just like an input jack and where do i ground it to, theres a ground but its empty and cant clip to it.

author: jh15
author_rank: Frequent Contributor
timestamp: March 22, 2018, 04:10:29 am
content: ground your probe where it says ground nearby. I is a banana jack, but just hold your probe ground lead to it. You probably have an alligator clip lead on the probe.Just stick the tip of your probe there. If you have the 'witch's cap' pull back to protrude the hook and touch it there. If you take it off, or likely possible, it is missing, just touch the pinpoint of your probe there.Some may say this is a troll or a joke, I've been there, done that, got the tee-shirt, and explained to EE's that they did not have to return their new instrument batteries I installed to the factory to be charged.Likely it was quality assurance engineer, forgot.60 mhz analog with digital features is a nice find.Please don't blow it up look at dave's "how not to blow up your oscilloscope" video. You need to read and understand that.If a bit technical, ask here.

author: BravoV
author_rank: Super Contributor
timestamp: March 22, 2018, 04:32:35 am
content: You should download the manual and spend sometime there 1st, even you don't not understand it 100%, at least you will have an idea how to do basic scope preparation before using it.Some T&M equipments do need some pampering when powered on for the 1st time, not like say a DMM.

author: JS
author_rank: Frequent Contributor
timestamp: March 22, 2018, 05:31:36 am
content: You are using your phone audio out (~20kHz bandwidth) to output a 4kHz square wave, so you would be just getting up to the 5th harmonic, that's only two useful harmonics as only odd ones matter here. To get the perfect square you need infinitly many harmonics, with 7 you might have a reasonable response. Try 1kHz square and come back!Your probes should be compensated as someone already said...JS

author: XMA
author_rank: Contributor
timestamp: March 22, 2018, 06:49:43 am
content: thanks for all the replies, okay so when I do touch the scope probes to the probe adjust I get a perfect square wave, so then it's my phone that's putting out a bad square wave.

author: JS
author_rank: Frequent Contributor
timestamp: March 22, 2018, 06:57:09 am
content: Quote from: XMA on March 22, 2018, 06:49:43 amAs I explained, a "bad" square wave is expected from the phone at that frequency, it isn't doing anything wrong or failing, it's just it's bandwidth, and the representation of a limited bandwidth square wave is quite similar as you are seeing.JS

author: Performa01
author_rank: Super Contributor
timestamp: March 22, 2018, 02:09:35 pm
content: Apart from probe compensation and source bandwidth, this looks like an AC-coupled signal (the slanted roof and bottom) - which makes sense, since the phone would sure have an output coupling capacitor, doesn't it?

author: bson
author_rank: Unknown
timestamp: March 22, 2018, 07:57:01 pm
content: Check that the scope inputs aren't set to AC coupling. If so, switch over to DC.

author: w2aew
author_rank: Super Contributor
timestamp: March 22, 2018, 09:15:27 pm
content: Quote from: XMA on March 22, 2018, 06:49:43 amThe smartphone based function generators are notoriously ugly for most waveforms other than a sine wave.