[sdiy] oscilloscope considerations

[harry]

RE: Analog vs Digital scopes

Both have their place. If I could afford it, my first choice would be the
Analog
Digital Hybrid such as a Fluke Phillips model I use at work. It was in the $10K

range... a little too pricey for me.

The big advantage is being able to see both the pure analog signal (without all
the
fancy tricks) and then switch to digital.

Digital scopes can Alias... the too-low sample rate can make signals appear
that
do not exist... often fooling newbies (and experienced engineers alike) to
think
they are looking at (let's say) a 20KHz waveform when in reality its an
undersampled
200KHz waveform.

Another nasty digital trick is what happens when you view "noise" such as white

noise. The "all-frequency" content of this wave almost guarantees it will alias
and
display trash !  Because you are sampling at a regular rate... you can get
fooled easily
into thinking you are seeing a periodic waveform, when you are not.

That said... I'm considering a digital such as the low-end Tektronix ($1.5 - 3K

price range).  I'm just afraid that the LCD display speed (slow) will really
piss
me off.  I'm also afraid that the toy will break in a few years (like 3-5) and
be
unrepairable due to lack of parts.  Older analog scopes can last 20 years,
easily...
until the CRT decays to the point of darkness  (the equivalent of having a
slower
and slower scope)

Maybe those who have some more change might want to have two scopes. I've been
doing a quantizer lately... and the triggering on my analog scope sucks... and
two
channels is not enough for my spoiled @ss !!!

I'd say... If I had to have only one scope, It would be an ANALOG storage
scope.
I could live with that (even used...).  I'd go for no less than 60MHz for DIY
work

H^) harry

media at mail1.nai.net wrote:

> 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!! :)

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