[sdiy] oscilloscope considerations

[Bob Roesler]

The highest frequency in american (NTSC) composite analog video is 3.58
(actually 3.579545 as I recall) Mhz. It is the subcarrier used to encode
decode chrominance information. Composite digital video has a pixel rate of
4xsubcarrier (14.31818Mhz). The (relatively) industry standard (CCIR601)
component digital video is roughly the same rate, though it's not based on
subcarrier frequency, but rather a standard fixed clock rate that could be
shared amongst the NTSC & PAL world. Seems like 200Mhz, though plenty fine,
might be a little more than one would need for most video. At least this
goes for video for standard definition television.

my2bits

Bob



----- Original Message -----
From: "Scott Evans, Gen Mgr" <esresource at earthlink.net>
To: "DIY" <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, January 01, 2002 12:54 PM
Subject: Re: [sdiy] oscilloscope considerations


> I will second JH's remarks here. Unless you want the scope to work for
> video as well (100-200mhz recommended here), a 20mhz scope is plenty for
> audio DIY. The dual trace is very handy to explore wave forms in two
> areas of a circuit at the same time. You can overlay one wave form on
> top of another to check for wave form changes (desired or not). Also, a
> triggered time base is useful.
>
> I picked up a used Tek 465B on ebay for $200 and sent it out for
> calibration. This is a 100mhz scope. You can find dual trace 20-40 mhz
> stuff for less. I here that Leader makes some nice scopes in this range.
>
> Good luck,
>
> Scott Evans
>
> jhaible at t-online.de wrote:
> >
> > 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!! :)
> > >
> > >
> > >
> > >
> > >
> > >
> > >
>
>
>