[sdiy] Oscilloscope question

[Jerry Gray-Eskue]

Justin,

You need some type of storage scope (analog or digital storage) for low
frequency signals. An old trick is to crank up the brightness of the display
so you get an after glow of the trace. You may need to have the room
lighting dim to see the after glow trace. Old analog storage scopes with
CRTs worked this way, I don't know if this will work for your scope. Another
trick was to photograph the scope display with a long shutter time, there
used to special hood that mounted a Polaroid camera to do this, you might be
able to fake this setup using a cheap digital camera.

- Jerry
-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Justin Owen
Sent: Sunday, February 21, 2010 9:10 AM
To: SDIY List
Subject: [sdiy] Oscilloscope question


Hey all, I have scope question that's now bugging me enough that I'd like to
get an answer to it.

I have a 20Mhz Gould dual trace scope which, as cranky as it sometimes is,
has served me well this far.

On the 'Time/CM' setting (which sets both traces) I can get down to about
0.5 seconds before the trace starts flashing or pulsing (sorry - not sure
what the technical term for this is) - it's like the 'refresh' time/speed is
getting slower. At 5 seconds I have a dot going across the screen as opposed
to being able to see a complete waveform or line/measurement.

Problem is, when measuring low frequencies (let's say 20Hz to LFO range) to
view an entire cycle I need the Time/CM setting above 0.5 seconds - which
makes it almost impossible to check the quality or shape or whatever of a
waveform.

Right now I'm working on a kick drum oscillator - and for those big long 808
style Booooooms - that's a long old waveform - but it's almost impossible
for me to see it in its entirety.

So - if I wanted to look at a scope that could display an entire cycle or at
least more info about lower frequency waveforms/signals but with the refresh
rate of higher frequencies - what sort of specs should I be looking at?

Maybe I should mention at this point that I only paid a tenner for my
current scope. :)

Thanks much.

Justin



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