Author Topic: Oscilloscope training class (long)  (Read 133094 times)

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Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #75 on: May 01, 2012, 12:14:19 AM »
I added another video over the weekend, showing how to use a pair of 555s and a pair of NPN transistors to create a "marker" on the trace(s) of an old analog scope by applying a sweep-synchronous, delay-adjustable pulse to the Z-axis input.
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Offline BravoV

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Re: Oscilloscope training class (long)
« Reply #76 on: May 01, 2012, 02:37:31 AM »
Alan, thanks for this excellent tutorial, I've been looking for a good practical example using that extra Z axis input, yours is the best imo.

Did a quick circuit capture from that video to complete that video, hope you don't mind.

« Last Edit: May 01, 2012, 02:43:12 AM by BravoV »
 

Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #77 on: May 06, 2012, 02:34:53 PM »
I added another "Back to Basics" video to my channel tonight - showing how to make a frequency measurement on an analog scope.  Enjoy...
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Offline Chris Wilson

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Re: Oscilloscope training class (long)
« Reply #78 on: May 17, 2012, 08:23:50 PM »
Re your circuit for checking modulation of amateur radio transmitters on a `scope. Someone who saw my effort at recreating this box of tricks has told me not to use it to monitor transmission on air, as diodes can cause frequency multiplication and cause me to transmit spurious harmonics. I am not sure if germanium diodes can cause this, what's the score with using it to monitor real time transmission on air please Alan? http://www.chriswilson.tv/RF/rf.html is my attempt. Forgive the rusty nuts, I built it at home at the weekend, with no access to my my normal boxes of hardware odds and sods at work (I am in the race car game). Cheers
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Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #79 on: May 18, 2012, 12:50:31 AM »
Re your circuit for checking modulation of amateur radio transmitters on a `scope. Someone who saw my effort at recreating this box of tricks has told me not to use it to monitor transmission on air, as diodes can cause frequency multiplication and cause me to transmit spurious harmonics. I am not sure if germanium diodes can cause this, what's the score with using it to monitor real time transmission on air please Alan? http://www.chriswilson.tv/RF/rf.html is my attempt. Forgive the rusty nuts, I built it at home at the weekend, with no access to my my normal boxes of hardware odds and sods at work (I am in the race car game). Cheers

Yes, he is correct.  Any diode, germanium or not, is a non-linear device, and will generate harmonic distortion products as well as intermod products.  While these diodes are not "in" the RF path, they are tapped onto it.  Thus, there will be a small amount of harmonic components injected back into the RF line - both through the coupling cap as well as from simple stray pickup through the air.  The latter can be reduced by shielding the detector circuit from the main RF thru-path.  Lowering the load impedance seen by the detector will also help.  In my tests, these distortion products were 45-50dB down or more from the main signal.  So, technically, he is correct, and you should be careful regarding this.  You can check it yourself by listening for your third harmonic (3x your operating frequency), which will typically be the largest product generated.  Maybe have a buddy listen to your main signal, then listen for you at 3x that frequency.  It is likely that you will not be heard at 3x.  However, it is definitely worth checking out to be sure that you are being compliant with spurious emission levels.

The simple resistive divider used to monitor the RF envelope (the most useful thing anyway) will not introduce any distortion effects at all.

Note also that the demodulator circuit is typically used for linearity measurements of an amplifier.  Thus, the demodulator would be connected to the RF before the amp, and the resistive monitor connected after the amp.  The only reason that I have both of these circuits connected to the same RF line was to demonstrate the function of each circuit - they'd never be used simultaneously in this way.
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Offline Chris Wilson

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Re: Oscilloscope training class (long)
« Reply #80 on: May 18, 2012, 09:37:49 AM »
OK, thanks, I'll be very careful with it, probably just use it into a dummy load for now. I can "borrow" a friend with a spectrum analyser at some point ;)
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Offline Bonati

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Re: Oscilloscope training class (long)
« Reply #81 on: June 09, 2012, 12:12:59 AM »
Alan these videos are wonderful, thanks for doing them. Learning a bunch!
 

Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #82 on: June 10, 2012, 06:09:43 AM »
Alan these videos are wonderful, thanks for doing them. Learning a bunch!

I'm very glad that you are enjoying them.  There are plenty more on my Channel that I haven't posted here.  And, I'm always up for suggestions for new video topics that you'd like to see.  I'm just trying to live up to the quality of Dave's videos!
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Offline Devian

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Re: Oscilloscope training class (long)
« Reply #83 on: July 07, 2012, 10:20:58 PM »
Thank you for this, it is really impressed and I will finish watching.
 

Offline kingjay1

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Re: Oscilloscope training class (long)
« Reply #84 on: August 24, 2012, 11:40:25 AM »
So exciting and helpful.Compare to the book knowledge , these videos give me something more.
 

Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #85 on: August 25, 2012, 11:49:29 AM »
So exciting and helpful.Compare to the book knowledge , these videos give me something more.

I'm glad you enjoyed the video(s).  Please let me know if there are other topics that you'd like to see.
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Offline kg4arn

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Re: Oscilloscope training class (long)
« Reply #86 on: August 26, 2012, 02:21:06 AM »

[/quote]

I'm glad you enjoyed the video(s).  Please let me know if there are other topics that you'd like to see.

[/quote]

I would like to see your take on compensating the scope probes that have both the low and high frequency compensation trimmers.
And if you would explain why some probes have both and some only have the low frequency compensation.

I have Agilent N2863B probes.   There is a trimmer in the tip which is adjusted using the familiar 1KHz square wave output from the front of the scope.  There are 2 more trim adjustments for the high frequency at the base of the probe where the BNC connects to the scope.  It appears that a fast rise time step is used to make the adjustment.

I have seen some other manufacturer's probes with this set up as well.  Here's one from Pico Technology

TA049:  500 MHz  Oscilloscope Probe x10

The TA049 is a passive high–impedance oscilloscope probe designed and calibrated for use on instruments having an input impedance of 1 M?  shunted by 15 pF. However, it may be compensated for use with instruments having an input capacitance of 10 to 35 pF. The probe has a further three trimmers for high–frequency compensation adjustment
[/u]

 

Offline BravoV

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Re: Oscilloscope training class (long)
« Reply #87 on: September 02, 2012, 02:20:35 AM »
Re-posting a link here another w2aew's excellent video -> http://www.eevblog.com/forum/beginners/new-tutorial-video-basics-of-plls/


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Re: Oscilloscope training class (long)
« Reply #88 on: September 06, 2012, 12:22:09 AM »
Thumbs up!!I really like them,but dont got enough time to watch  all,could u recommend  some?
 

Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #89 on: September 06, 2012, 10:09:52 AM »
Thumbs up!!I really like them,but dont got enough time to watch  all,could u recommend  some?

Let me know what topics you want to learn about, and I'll recommend any of mine that might be of help.
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Offline Alana

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Re: Oscilloscope training class (long)
« Reply #90 on: September 12, 2012, 03:34:35 AM »
I loved the main video and entire cycle of materials showed by w2aew.
For me this is kind of "back to school" and school lab.
Which reminds me, in our oscilloscope classes we had sort of practical exam on how to make oscilloscope draw a line, two lines, dot, two dots - all using function gen and xy mode. This may be a good idea for another video, or on checking if people in class understand the basics.
 

Offline arekm

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Re: Oscilloscope training class (long)
« Reply #91 on: September 12, 2012, 03:53:51 AM »
I would like to see some info about using oscilloscope with high voltages (like 1-2kV) in inverters or power sources in analog oscilloscopes or analog tv.
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Offline Chris Wilson

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Re: Oscilloscope training class (long)
« Reply #92 on: September 25, 2012, 05:52:35 PM »
I too would like to see details on the safe viewing of high voltage DC power supply ripple. I am building a couple of supplies for big RF generators, one 3kV and one 5kV I also want to view the AC output of the transformers when they are under load. Thanks, it's a great resource Alan.
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Offline awkhim

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Re: Oscilloscope training class (long)
« Reply #93 on: September 26, 2012, 05:35:36 PM »
where i can buy the cheaper price for digital oscilloscope my requirements is 100 MHz, dual channel and there's a data we can save
 

Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #94 on: November 11, 2012, 05:38:57 AM »
I added a few more videos over the last several weeks. The most recent is a basic tutorial on how to use the FFT function in a digital oscilloscope.
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Offline MrQuan

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Re: Oscilloscope training class (long)
« Reply #95 on: November 27, 2012, 09:47:36 AM »
Hi w2aew,

Just wanted to say I found your AC/DC coupling video on YouTube and it was very helpful. Big fan of all your oscilloscope videos. Cheers :)
 

Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #96 on: December 07, 2012, 02:43:57 PM »
I posted another video in the "scope basics" series tonight - this one talks about oscilloscope probe ground lead length, and it's affect on measured signal integrity.


« Last Edit: December 07, 2012, 02:47:04 PM by w2aew »
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Offline nadona

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Re: Oscilloscope training class (long)
« Reply #97 on: December 27, 2012, 08:10:59 PM »
@w2aew;
I have a question about my Hantek 200MHz. Why is the square wave Rise Time change when the FG frequency change?  For example; [email protected], [email protected], [email protected], [email protected], [email protected]

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Offline w2aew

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Re: Oscilloscope training class (long)
« Reply #98 on: December 28, 2012, 03:52:06 PM »
@w2aew;
I have a question about my Hantek 200MHz. Why is the square wave Rise Time change when the FG frequency change?  For example; [email protected], [email protected], [email protected], [email protected], [email protected]

Regards.

Making the assumption that you are changing your horizontal time scale (sweep speed) at the same time that you are changing the FG frequency, I would say that the change in rise time is not real.  It is due to the fact that the at the slower horizontal time scale setting, the effective sample rate is decimated (lowered), reaching a point where very few if any samples actually land on the rising edge at all.  The scope interpolates between the waveform points.  At the lower effective sample rate, the interpolated waveform between these widely spaced points does not accurately reflect the true rise time. To test this hypothesis on your scope, setup the 100k or 1MHz square wave and make the rise time measurement.  Without changing the horizontal controls, simply change the square wave frequency on the FG down to 100Hz.  You should still have a rising edge on the screen, and it should still be reading the same fast rise time.  This is the true rise time.  If the rise time slows as you move the horizontal timescale to a slower setting, then the scope is lying to you at these lower speeds due to the sample rate decimation.

This is a fairly common problem, that measurements are made on only the displayed point or on severely decimated samples.  Some scopes give you the ability to control the sample rate and memory independent of the horizontal sweep settings so that this type of distortion due to under sampling can be avoided.

However, if the experiment above (changing FG frequency, leaving scope horizontal alone) results in slower rise time at slower FG frequencies, then it has nothing to do with the scope and is a property of the FG.
« Last Edit: December 29, 2012, 03:05:20 AM by w2aew »
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Offline nadona

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Re: Oscilloscope training class (long)
« Reply #99 on: December 28, 2012, 07:20:08 PM »
@w2aew;
"To test this hypothesis on your scope, setup the 100k or 1MHz square wave and make the rise time measurement. Without changing the horizontal controls, simply change the square wave frequency on the FG down to 100Hz.  You should still have a rising edge on the screen, and it should still be reading the same fast rise time.  This is the true rise time. "

Exactly! Same rising edge & same rise time.

As usual, thank you very much for your detailed explanation.

Regards.
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