a beginner question - scopes

[Martin Czech]

> Hi list.
> 
> I am needing (arg) to buy an oscilloscope. At the local shop they adviced me a pc based one, saying it was a cheap alternative to classic models, a bit more expensive then cheapcheappo models but far more reliable. What do u guys'n'girls think? Is this worth it? Is it precise enough for audio based circuits? Please tell me..as they ordered it for me, but i think i can still say no if i'm quick enough... i'm **hesitating**.. maybe a cheapo one could do the trick for me? (but they're not THAT cheaper compared to pro scopes they talked to me about...) So maybe u could at least tell what characteristics i DO need from a scope...
> thanx
> 
> greg.

Greg, this is like the washing machine story, you know... When I was young
(;->), I thought it would be a good idea to save money and so I bought
a used one, . Ok, after one year it broke down in a cloud of smoke,
the service man said "not repairable", charged me with 40DM (you know
Zappa's Flakes?)  and disappeared. I had to pay for the removal of the
old machine also, alltogether 990 DM.

And then I was enlightened. I went to the local shop and bougth the
most expensive, highest quality machine (a Miele). Cost me an awfull
lot of cash.  Dropped it in into th e cellar, and it works, and works,
and works..... Never any problems, peace of mind.  I'm shure this was a
good deal, cheapo machines would have cost me a lot of grief and repair
money, so it is a reall cost saver.

A few weeks ago, I was in the same situation, trying to find a scope. Well
I tryed the cheapo first, and then I remembered, man... don't be
stupid, a scope is a lifetime buy, so I took a reasonable scope with
150MHz bandwidth, dual timebase, processor controlled, and user menu
callibration. For 2300 DM. (1$ = 1.67 DM).  Today I get it from the
post office.

The scope is the main tool on the electronic workbench, I don't want
to work with crap tools.

The simple DSO you can get for a PC today seem to be quite crappy.
Very limited analog bandwidth, no spec for ADC resolution, no specs for
display refresh times ... etc. In general no specs at all. You didn't
mention any specs in your mail... This is supposed to be a measurement
tool, if it has no specs, now, what should this be ?  In most cases such
a PC slot card may do, there are others where it won't.

And the better ones (I've seen a 60 MHz bandwidth recently, Conrad
Electronic) go straight into the 1000 DM direction.

Even the really high price DSO here at work (that we bought a couple of
years ago) have quite slow aquisition rates, so if you have a sporadic
problem, but you can't trigger it right, you most probably won't see
it. In these cases it is time to pull out the good old Tektronics analog
scope, ahhh there is the glitch.

DSO manufacturers know this problem, they try to make their scopes faster
to give them a more analog feel in the readout.




So: be very carefull to where you spend your money! At least you should
try the PC scope card in the shop, or even better at home. Try e.g. a
burst signal that has very low mark/space ratio. Try higher frequencys,
go to the analog bandwidth limit. Never buy it blind.

You get nothing for nothing.

And remember my washing machine...   ;->

m.c.