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Old 8th May 2008, 06:03 PM   #1
pjpoes is offline pjpoes  United States
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Default Buying first Oscilliscope

Hi guys, I'm looking to buy my first oscilloscope and was wondering what was a good recommended model. It will primarily be used to test analogue circuits, mostly amplifiers, but will likely be used in testing some digital gear. I was told I need more than 10mhz range, and that 100 was best? I was told that while digital will likely be better than analogue, that the analogues will be the better value.

Also, what type of leads should I be looking at, accessories, etc. I know I need dummy loads for the amplifier testing, signal generator, but what else should I be thinking about. I found a source for some 500 watt and 1000 watt high power resistors in various values from China, and will likely use that for the Dummy Load. They are non-inductive and quite affordable (other than shipping), so I will see if they work. I've been told these can be good if you place them in a bucket of water to help dissipate heat. I would imagine that large heatsinks attached, fans, etc would all also be viable alternatives.

I've also read that you can measure distortion with an Oscilloscope, how do you do this? Distortion is another feature I'm interested in measuring. Thanks in advance.

p.s. I figure if I'm going to be investing all this time and money into the hobby, might as well be prepared to do it right. I just finished a small shopping spree for speaker measurement equipment (Woofet Tester 3, ATB PC Pro, and speaker workshop (free of course), and spent some time learning to use all this. Now I want to measure some of my amplifier projects.
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Old 8th May 2008, 06:17 PM   #2
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Default Scope

The higher the bandwidth of the scope, the less sensitivity it will have, and the more noise will appear on the trace if used at lower sensitivities. 10MHz is more than enough for 99.9% of audio jobs, but maybe not for digital.

Personally I use an older HP182C scope with several "Plug Ins" that allow me 100MHz bandwidth and 1mV sensitivity for general use and finding VHF oscillations, but also 500kHz bandwidth with 100uV sensitivity - which is very handy to chase noise. It was bought off ebay for a grand total of $300 - mainframe and plug ins - and it's a beautiful piece of wark that would have cost the price of small BMW when new 25 years ago. And it has a very large screen!

Tektronix is the other top brand, I would be happy with something really professional from either company, and at the throw away prices they are now, why buy newer (but way lower quantity) stuff?

Regards, Allen
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Old 8th May 2008, 11:51 PM   #3
pjpoes is offline pjpoes  United States
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Thanks, I will look for one that fits my needs then. Sounds like I would be just fine with a 10 or 20mhz unit, and could probably save a little money.
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Old 9th May 2008, 12:31 AM   #4
pjpoes is offline pjpoes  United States
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ebay special

Are these any good? I see them on ebay, and at 350 dollars you get a 25mhz 2 channel digital storage 0-scope, seems like a good deal.
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Old 9th May 2008, 01:58 AM   #5
TheMG is offline TheMG  Canada
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I might be wrong, but to measure distortion I'm pretty sure you need a DSO (digital storage oscilloscope) for the FFT/DFT function, or alternatively a spectrum analyzer (or analog scope with spectrum analyzer plug-in). Unless you want to go pro and get a dedicated distortion analyzer.
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Old 9th May 2008, 02:05 AM   #6
x-pro is offline x-pro  United Kingdom
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Quote:
Originally posted by pjpoes
ebay special

Are these any good? I see them on ebay, and at 350 dollars you get a 25mhz 2 channel digital storage 0-scope, seems like a good deal.
I would say that these are toys, not serious instruments. I keep a relatively cheap Agilent DSO3062A as a digital scope (and it is much better than these OWONs), however I use mostly an old but excellent Tek 2467 - it is a lot more convenient for most applications. To have just one digital scope is only possible, IMHO, if you go all the way up to "digital phosphor" Tektronix scopes. Otherwise cheap digital scopes are not good enough for analogue apps. If you need to record the trace or catch a digital pulse then a digital scope is very useful. But if you would like to observe what happens in the circuit real-time you need either an analogue scope or an expensive digital one.

You can get 300-400MHz Tek 2465/65A/65B for under $400:

http://cgi.ebay.co.uk/ws/eBayISAPI.d...MEWA:IT&ih=001

and it would be a lot more help than a new digital for the same money, I think.


Alex
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Old 9th May 2008, 10:49 AM   #7
joir is offline joir  Iceland
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Default Depends on budget :)

I bougth a scope from ebay on a fairly tight bugdet last year and opted for a used two channel(a must) 20Mhz analog scope. If budget would not have been an issue I would have bought a new digital scope with all bells and whistles I've used good HP digital ones and they are a dream to work with. But my spartan scope is all I need, it displays signals and I can read time and amplitude by counting the grids on the display (99,9% of usage).

One thing to keep in mind is that buying a cheap analog one over expensive one (analog or digital) is that when you start working with a scope and reading/learning you get the feel for what it is that you need and want and then an upgrade is less painfull But as I stated before it is not an option to buy a single channel scope.

I would also suggest trying to buy a scope with probes as probes on their own are not that cheap.

As for models then Tek, HP to name some are popular and very good. Although I opted for a Kenwood scope because I had used them before and was content, also you can get lesser known brands for less $ as fewer people bid for them

In regard to distortion measurements then you can see difference in waveforms on a scope and in a way "see" the distortion but for real measurement I think it would be more cost effective to buy a seperate freq. analyzer as oppesed to a scope with one integrated.

Note that if you buy used measurement equipment be prepared that it could be somewhat out of calibration.

Good luck and remember that any scope is so much better then no scope
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Old 9th May 2008, 12:56 PM   #8
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I have 3 scopes in pretty regular use -- a Tektronix 2465 which I was able to get with a current calibration, a TDS3012B which is on all day long, and a 5223 -- an old but extremely quiet analog scope with digital memory. 2465's and the like were the top of the line for analog from TEK at the time.

If you have the room the 7000 series are pretty inexpensive and have a plethora of plug-ins, even spectrum analyzers which range from the audio band to UHF.

I purchased a Texas Instruments development board/evaluation module for their 24 bit ADC -- the ADS1271EVM -- there's a screen shot on this page:
distortion analyzer recomendations?

i plan to write some routines for the eval module this summer.

the distortion number it comes up with is consistent with that obtained from my AP and Tektronix distortion analyzers -- but if you want to measure above 1.8V you need to put an attenuator in front of the device.
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