[sdiy] oscilloscope considerations

[jhaible at t-online.de]

I'm using one of these "expensive Digital Phosphor" scopes
at my day job, where strange trigger conditions are important,
the frequency range goes up to 1GHz, and documentation of 
waveforms is crucial.

For the work on analogue synthesizers, however, I prefer my
unexpensive 30MHz dual channel analogue scope. 
In fact, I have built 90% of my synthesizers using a 150-Dollar
(new ! I've bought it used for 100 ...) 20MHz single channel
scope. Over the years the pots became scratchy, and 2 channels
are an improovement really. So I upgraded to a dual channel 
analogue scope for approx. 300 or 350 Dollars. It's all you
need for analogue audio stuff, really. It does not have a
noisy fan, and - most important - the beam is connected directly
to the analogue input - no digital scope will give you the
same immediate access to your signals, not even the DPO stuff.

Working with both, high end digital and unexpensive analogue
scopes is very different. On the digital, you can catch glitches
in their full beauty, once you have set the right trigger conditions,
and - important - if you know there is something to look for at all!
On the analoge, it's more likely that you see when something is
wrong for a tiny moment. You may not see it as precisely, but it's
less likely that it escapes your perception at all.

JH.


media at mail1.nai.net schrieb:
> 
> I know many people on this list frequently suggest buying 
> a used 
> oscilloscope from Ebay, Nuts & Volts, and a Ham 
> flea-markets.  The Ham flea 
> market might not be a bad idea for me since Newington is 
> less than two 
> hours from here.  However, I'm considering buying a new 
> scope for two 
> reasons.  Firstly, I'm not familiar with all of the makes 
> and models, and 
> do not know which features each model has, or its fair 
> market price. 
> Secondly, I want to make sure that it is calibrated and 
> working properly, 
> as fixing an oscilloscope without an oscilloscope would 
> seem impossible. 
> So waiting for a dealer to blow out an older model might 
> be my best bet. 
> 
> Is there a FAQ or website that discusses features of 
> various scopes??  The 
> manufacturer websites haven't been all that helpful as to 
> what features are 
> actually useful.  Nor could I find descriptions of scopes 
> no longer being 
> made.
> 
> Prices range from an Instek 5MHz analog scope for $235, 
> to digital scopes 
> costing over $16K!!  While I do not think I need a 
> digital scope, that 
> seems to be the way things are going, as a number of 
> manufacturers no 
> longer make analog scopes.  What is the real advantage of 
> an analog scope?? 
> The problem with anything digital is not so much the 
> price, but that it 
> doesn't hold its value -- digital technology keeps 
> getting faster and less 
> expensive every year.
> 
> There seem to be four types of digital scopes: digital 
> scopes with LCD 
> displays (eg. Tektronix TDS210), digital scopes with CRT 
> displays, digital 
> scopes with CRT displays that claim to have an "analog" 
> mode (eg. BK5020), 
> and expensive scopes from Tektronics called Digital 
> Phosphor Oscilloscopes 
> (DPO) that have VGA color LCD displays that supposedly 
> imitate the display 
> characteristics of analogue scopes.  I cannot afford a 
> DPO, but the digital 
> scopes with either monochrome CRT or monochrome LCD 
> screens seem 
> competitively priced.  Any ideas here??
> 
> Another consideration is bandwidth.  I'm thinking that 
> 20MHz would be fast 
> enough for sdiy, but I have heard many people say that 
> 20MHz scopes should 
> be avoided.  Why is that??   As far as digital scopes are 
> concerned, sample 
> rates also vary.  I would think the two would be related, 
> but there doesn't 
> seem to be a correlation in any of the specifications.  
> Also, there is no 
> mention of resolution (ie. bit depth), which strikes me 
> as very odd for an 
> instrument that measures voltages against time.
> 
> Most of the digital scopes include communications ports 
> or have them 
> available as options.  Is there any sort of standard data 
> format for 
> oscilloscopes, or are you stuck with the software 
> available for one brand 
> of scope??  Several of the digital scopes also have 
> software plug-in 
> modules that add features, such as FFT.  I think FFT 
> could be very useful. 
> However, considering that the computer hardware is 
> already there, there 
> seems to be a lack of acoustic analysis software compared 
> to what available 
> for the Techron and Goldline hardware.
> 
> Is there anything else I should consider??  Any brands I 
> should avoid?? 
> 
> Finally, is there a dealer in the U.S. that anyone would 
> recommend??  I've 
> checked out Techni-Tool and Test Equipment Depot.  
> Tektronix also sells 
> reconditioned units at a discount.
> 
> 
> THANX!! :)
> 
> 
> 
> 
> 
> 
>