Re: [AH] buying an oscilloscope (was [AH] Visual patterns from analogue

From cheater00 .
Sent Sat, May 11th 2013, 22:54

The "vector rescanning" technique is not possible on DSOs because they
alias waveforms. DSOs also suck for stuff like Lissajous patterns and
in general x-y display. But unless you get a bistable analog storage
oscilloscope like one of the Tektronix 7000 series bistable storage
scopes that start at around $400 used you have to use a digital scope
to see slow signals like CVs. Those are, however, well suited for
analysis via line-in - just get an analogue volt meter with recorder
output, select the right range, and take the output into your sound
card.

When buying any scope, make sure it can do XY mode, that it's at least
dual trace, that it can subtract signals (A-B), and that it has
1Megohm inputs, not 50 Ohm ones.

Try to go for scopes where the CRT uses at least 20 kV acceleration voltage.

When buying a scope from ebay, ask the seller if it has any burn-out
(don't buy one where there's something burnt into the phosphorus, like
on an old TV). Ask the seller to use the scope's callibrator (most
scopes have one, if not ask him to use an external one). The
callibrator is a square wave generator. Ask the seller to take a
picture of the scope displaying an image of the calibration signal on
each channel at once, such that the waveforms cover 80% of the
screen's height. Make sure the square waves aren't lopsided or curvy,
that there's no ripple, and that the traces aren't thick (a sign of
noise).

When buying in person, make sure to plug it in and see if it works,
use the procedure above.

Always ask if probes are included. It's a hassle to get extra probes.

Once you get it, let it run for a couple days without shutting it off.
Make the trace very dim (just barely visible) so that it doesn't burn
anything in to the phosphorus, or even turn it down completely. See if
it still works afterwards. Don't give out any ratings until you've
done that.

Learn what triggering is and check if it works. It's useful. A scope
with external trigger is useful for displaying synth waveforms and how
they react to filters etc, but only if you have a modular with a
counter.

Cheers,
D.

On Thu, May 9, 2013 at 1:54 PM, Thomas Strathmann <thomas@pdp7.org> wrote:
> On 08.05.13 21:31, Nicole Feeder wrote:
>> I bought an oscilloscope a few years ago. I looked around a lot for a
>> used one, but it was tricky for me to find something at the time. I
>> ended up settling on a small, new digital scope - Rigol DS1052E 50MHz.
>> I've been happy with it. It isn't quite as nice as some of the
>> Tektronix's scopes I have used, nor as sensitive and whatnot as some
>> analog scopes, but I was spoiled in the physics department for years.
>> For under $400 it is a nice, reasonably sized scope that fits on my
>> bench well and has good functionality.
>
> Seconded. I've got the 100MHz version which is basically the same
> machine. Compared to other (often fancier) digital scopes in the same
> price segment I'd say that the Rigol definitely feels sturdier and not
> as wobbly in day to day use. Although it should be noted that there are
> probably some DSOs that are quieter in operation. The fan in the Rigol
> is not the best possible one (a small, high-speed, low-cost thing). All
> in all I don't regret buying it and wouldn't go back to analog for most
> measuring tasks I do.
>
>         Thomas