Out with the old, In with the new, Scope that is

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Perhaps a few other "oldtimers" have built or played with a Heathkit oscilloscope. I built lots of their kits.

My Model 10-14 scope let out a muffled pop and a cloud of smoke, with that awful burnt electrical odor, earlier this year.

It was a sad day when that happened, but a joyous one when a new Rigol digital scope showed up on the doorstep. It is truely so cool to be able to adjust the gain and timebase after the fact, and study the waveform at my leasure.

At 60MHz & 2GSa/S it is definitely not the high end of the line-up, but it works great, and I'm back in the game.

It was very hard for me to toss the old scope, and not to pop the cover. Its been too long since I did any tube work, though, and too many other projects in the que. Besides, it rattled when I carried it out to the trash, never a good thing for a fine piece of electronics.

I'm also not sure which weights more, the old scope, or my car.

JC

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Nice one, Doc!

I hope that new scope gives you as many good years of use as that old scope did.

To be honest, I kinda miss having an analog scope around.

I too built many Heathkits over the years, several of which were Oscilloscopes.

I really miss Heathkit. I remember getting the periodical Heathkit catalog, excited to see what new products they were offering. And I was just as anxious about how long it would be before I could buy the next new toy from them.

Those were the days!!!

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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DocJC wrote:
.. earlier this year.

Gotcha! I wondered how long it would be before someone failed to notice that it is now 2009 :lol:

Ross McKenzie ValuSoft Melbourne Australia

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Hi Carl,

Glad you had a good trip over the holiday!

Yes, Ross, you got me! Of course you were longer into the new year than I was when I made that comment... :wink:

JC

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I too got a Rigol, to replace my old analog Tektronix. Wonderful devices.

There are pointy haired bald people.
Time flies when you have a bad prescaler selected.

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Congratulations Doc, with this new scope. A good investment !

Nard

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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I

Quote:

A good investment !

I'm sure it is. 2GS/s is the same as my TDS2022B. :D

If you think education is expensive, try ignorance.

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Hi Daqq

Hello Nard. Happy Holidays. It makes a lot a measurements trivial.

JC

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I am thinking of getting a rigol scope myself.

I have a question, there are several rigol scopes in the same family, all sample at 2G/s, but the bandwith is between 50-200mhz. Internally what is the difference between the 50mhz scope and the 200mhz scope, since they both sample at the same speed?

Regards,

Alan To

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I'm not an expert, but my understadning is that the 50-200mHz is the bandwidth of the scopes analog front end, which feeds the ADC.

To accurately reproduce a waveform, with its bumps and dips, and sharp corners, (Square wave), you need to have enough bandwidth to pass all of the various frequency components which make up the signal.

A square wave, for example, is made up of an infinite number of sin wawes, of increasing frequency and decreasing amplitude.

In practice, if the signal is repetative, then a bandwidth that includes the fundamental frequency of the signal, and everything up through its 10th harmonic, will give a pretty good reproduction of the signal.

A 1 KHz square wave would look pretty good if the amplifier had a 10KHz bandwidth.

If the bandwidth is too little, the amplifier does not pass all of the higher frequency components. When you look at the signal a square wave will not look square. The edges will be sloped, not vertical, and the top won't form a 90 degree angle, but will have overshoot and ringing.

No time to add a picture right now, but hopefull this helps.

The sample rate tells you how many samples the scope took per second. If I have a 1 khZ square wave, and a 2GS/s unit, there are 2 milion samples making up each period of the square wave, ie lots.

If you have a complex waveform, and only a few samples making it up, you will miss details. On a square wave you may have a sample at 0 V and a sample at 5 V, but along the time line you do not really know when the signal switched high. The more samples you have, the better you can tell when it switched high.

Nyquist states that to take the samples and recreate the original waveform you must sample at > twice the highest frequency component in the signal. To recreate a 1 kHz sin wave I have to have sampled it at > 2 K S/s. Note that this will allow one to recreate a periodic waveform, the sin wave, but with only 2.0000001 Samples per period it is a pretty shabby looking sin wave.

So, the MHz rating is the front end of the scope. It if attenuates the signal there is no way you can see it accurately reproduced on the display. Running a uC with a 20 MHz clock, you could look at the clock signal with a 10 * 20 MHz = 200 MHz front end.

Note that you don't usually need to see the clock signal, or see it perfectly reproduced.

Note that the BW is actually the 3dB point for the front end, so the 200 MHz BW front end does not really pass a 200 MHz signal without some attenuation.

The sample rate needs to be viewed in context to the frequencies you are viewing. Think of it as graphing points on a paper. How many points are you using to draw the curve? The more the better.

JC

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http://cgi.ebay.com/Oszilloskop-...

What do you think about this one? Strangly cheap and the guy's got a lot of them.

There are pointy haired bald people.
Time flies when you have a bad prescaler selected.

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http://www.rtr.ca/welec_w2022a/

I would not touch the welec

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DocJC wrote:
I'm not an expert, but my understadning is that the 50-200mHz is the bandwidth of the scopes analog front end, which feeds the ADC.

To accurately reproduce a waveform, with its bumps and dips, and sharp corners, (Square wave), you need to have enough bandwidth to pass all of the various frequency components which make up the signal.

A square wave, for example, is made up of an infinite number of sin wawes, of increasing frequency and decreasing amplitude.

In practice, if the signal is repetative, then a bandwidth that includes the fundamental frequency of the signal, and everything up through its 10th harmonic, will give a pretty good reproduction of the signal.

A 1 KHz square wave would look pretty good if the amplifier had a 10KHz bandwidth.

If the bandwidth is too little, the amplifier does not pass all of the higher frequency components. When you look at the signal a square wave will not look square. The edges will be sloped, not vertical, and the top won't form a 90 degree angle, but will have overshoot and ringing.

No time to add a picture right now, but hopefull this helps.

The sample rate tells you how many samples the scope took per second. If I have a 1 khZ square wave, and a 2GS/s unit, there are 2 milion samples making up each period of the square wave, ie lots.

If you have a complex waveform, and only a few samples making it up, you will miss details. On a square wave you may have a sample at 0 V and a sample at 5 V, but along the time line you do not really know when the signal switched high. The more samples you have, the better you can tell when it switched high.

Nyquist states that to take the samples and recreate the original waveform you must sample at > twice the highest frequency component in the signal. To recreate a 1 kHz sin wave I have to have sampled it at > 2 K S/s. Note that this will allow one to recreate a periodic waveform, the sin wave, but with only 2.0000001 Samples per period it is a pretty shabby looking sin wave.

So, the MHz rating is the front end of the scope. It if attenuates the signal there is no way you can see it accurately reproduced on the display. Running a uC with a 20 MHz clock, you could look at the clock signal with a 10 * 20 MHz = 200 MHz front end.

Note that you don't usually need to see the clock signal, or see it perfectly reproduced.

Note that the BW is actually the 3dB point for the front end, so the 200 MHz BW front end does not really pass a 200 MHz signal without some attenuation.

The sample rate needs to be viewed in context to the frequencies you are viewing. Think of it as graphing points on a paper. How many points are you using to draw the curve? The more the better.

JC

Thanks for the reply.

I was wondering more about the specifics of the unit and not a general question about scopes itself.

Specifically, I was wondering if 2G/s was consistent among 50-100mhz units, or if 2g/s was different for different models with different BW.

If the 2g/s were the same, then what is the real difference between the models with different BW, is it some digital filter in firmware, is it a physical aliasing filter, both or something else.

Regards,

Alan To

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@DocJC, thanks for the explanation, I found it very informative

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What is that small one on the left? Brand/model?
Thanks,
Kostya

DocJC wrote:
Perhaps a few other "oldtimers" have built or played with a Heathkit oscilloscope. I built lots of their kits.

My Model 10-14 scope let out a muffled pop and a cloud of smoke, with that awful burnt electrical odor, earlier this year.

It was a sad day when that happened, but a joyous one when a new Rigol digital scope showed up on the doorstep. It is truely so cool to be able to adjust the gain and timebase after the fact, and study the waveform at my leasure.

At 60MHz & 2GSa/S it is definitely not the high end of the line-up, but it works great, and I'm back in the game.

It was very hard for me to toss the old scope, and not to pop the cover. Its been too long since I did any tube work, though, and too many other projects in the que. Besides, it rattled when I carried it out to the trash, never a good thing for a fine piece of electronics.

I'm also not sure which weights more, the old scope, or my car.

JC

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Hi Emuler, sorry I missed you on my initial response.

Dingo, your welcome!

Daqq, The eBay offering looks interesting. It is a give-away price! I do not know anything about this make. It looks like Toalan wasn't to excited it, however.

Salat, The "Little Scope" is a Rigol, Model DS1062CA, (2 Channels, 60 MHz, 2GSa/s). I purchased it from Saelig, here: Saelig . This is one of several models in the lineup, it was on sale when I purchased it. It included a "free" case. I did not purchase the battery pack, as I intend to use it on my bench. I'm still learning its many features, and am very happy with it.

I think Steve purchased a Chinese DSO, and has been happy with it, but I do not have a link to his vendor.

JC