[sdiy] oscilloscope considerations

[media at mail1.nai.net]

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!! :)