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My recent Tek, Agilent, and LeCroy oscilloscope fun

M

Mr.CRC

Jan 1, 1970
0
John said:
Easier, and more dramatic, might be a spark gap. I think the first
cloud bounce work was done with spark gaps and PMTs.

A spark gap can produce a not-many-ns high-power light blip, small
enough to focus pretty well, parabola or big honking fresnel lens
maybe. That might appeal to a kid. Hey, make your own capacitor!

John

That's not a bad idea. Of course, a laser-induced air ionization spark
would be fun too!

Some folks are using laser sparks for broadband fast optical sources.

But I am having fun these days employing power LEDs to displace some Xe
arc lamps for Schlieren imaging light sources.
 
E

E

Jan 1, 1970
0
Mr.CRC said:
How's the waveform update rate on those things?

My Rigol (Agilent-branded one) updates about as fast as the lcd can display,
but then it only have 4k memory.

I bought a Tek TDS3014 about 7 years ago for home hobby use. That cost
me 2.5 years of my allowance. I don't regret it. At that time, the
TDS3000 series was where the price/performance breakthrough was.

I'm considering to get an Agilent DSO7034 350MHz in a few years, then
upgrade some time to the digital channels option. People spend a heck
of a lot more on Harleys and other useless toys.

I'd like to build a Q-switched YAG laser or N2 laser and do a time of
flight speed of light experiment for my daughter when she gets to a
grade where that will make sense. Maybe 3rd grade or so ;-) Might even
be able to get LEDs to do the job. I could probably measure it with my
100MHz scope, but 350MHz is a lot better.

I just tested how small time difference my 100 Mhz Rigol can detect:
about 0.5ns. If I feed both channels same signal they differ about 0.2ns

But my pulse generator is manual one ie. striking wires into solderless
breadboard damn fast, and that generates bit ugly signals.
Would be interesting to know what the risetime of those pulses is.
I am pretty sure it is under 1 ns but how much, that I don't know.
Anyone with a real scope wanting to experiment?

-ek
 
N

Nico Coesel

Jan 1, 1970
0
E said:
My Rigol (Agilent-branded one) updates about as fast as the lcd can display,
but then it only have 4k memory.

Actually there is no use to update the screen very fast. The human eye
can't deal with that. What most scopes with an LCD screen do is
combine many sweeps into one image and thereby simulating the good old
CRT scope. The oldest sweep has the least influence (displayed using
faint dots).
 
M

Mr.CRC

Jan 1, 1970
0
E said:
My Rigol (Agilent-branded one) updates about as fast as the lcd can display,
but then it only have 4k memory.

Waveform update rate on oscilloscopes is not the same as display update
rate. The latter is not particularly relevant. Waveform update rate is
essentially acquisition rate, not the sample rate, but the rate at which
triggers may be responded to and result in acquisition records which map
to the display.

Some scope architescures, such as Agilent 6000 and 7000 series, can
update 100000 waveforms/s. This can be done even if the time to fill
the acquisition memory is greater than 10us. For instance, at 4Gs/s, it
takes 1 ms to fill 4MB of acquisition memory. But on a 1us/div
horizontal scale, the screen represents only 10us of time. The scope
can on a setting like this achieve about 50000 wfms/s.

The importance of this is that if you have an intermittent anomaly, such
as a glitch or runt in a signal that occurs at 1ppm on a very fast
signal such as a memory bus transacting at a MHz, for ex., then if your
waveform update rate is only 10wfms/s, you have only a 1/100000 chance
of finding it in one second. Ie, it will take 100000 seconds to ensure
100% probability of finding it. (I may be over simplifying the
probability arithmetic here.)

However, with a scope that can capture 100000 wfms/s, it will only take
10 seconds to find the glitch.

This is one of the things worth paying up for with higher-end scopes.
I just tested how small time difference my 100 Mhz Rigol can detect:
about 0.5ns. If I feed both channels same signal they differ about 0.2ns

But my pulse generator is manual one ie. striking wires into solderless
breadboard damn fast, and that generates bit ugly signals.
Would be interesting to know what the risetime of those pulses is.
I am pretty sure it is under 1 ns but how much, that I don't know.
Anyone with a real scope wanting to experiment?

Interesting, I would have expected much slower response with just a
probe and long ground wire. But I can get 3.5ns rise time plugging my
probe into a 5V breadboard rail, on a 100MHz TDS3014. Since the rise
time of a 100MHz system is 3.5ns, this suggests that the actual input at
the probe tip is relatively impulsive (ie, much faster even) compared to
the scope front end.

I will try this at work with a 500MHz scope. In a few more weeks, I can
try it with the 1GHz scope.

This is clearly convincing me that I may need to go to a full 1Ghz scope
for my hobby electronic projects ;-)
 
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