RE: oscilloscope.. (fwd)

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Original poster: Gerry Reynolds <greynolds@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Fri, 22 Dec 2006 08:36:39 -0500
From: Leigh Copp <Leigh.Copp@xxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: RE: oscilloscope.. (fwd)

Chip,

A few points I would offer:

If you can afford/justify it, digital is the way to go. DSO's can store
single shot events such as transients, or intermittent problems. The
better ones have advanced triggering features that can capture
nanosecond anomalies that you would never catch on a phosphor CRT alone.
DSO's are getting pretty inexpensive these days.

That being said all DSO's are not created equal. You will hear about
sampling rate, real time vs. random equivalent time sampling, waveform
update rate etc. Digital Phosphor is a popular term out there, with a
couple of similar competitive technologies. 

How much speed and bandwidth do you need? A good rule of thumb is 2 X
the highest frequency of interest for repetitive sampled events, and at
least 
10 X, if you want to capture single shot events (real time sampling).
The faster you can sample the higher the likelihood of capturing that
elusive glitch. The caveat here however is the scope needs more memory
to hold those samples, and many models out there with high sampling rate
offer this at the expense of memory depth (record length - IE how much
data before and after the trigger event you actually can store).
Sampling speed is not to be confused with bandwidth by the way. Sampling
speed is just that; how fast the analog to digital conversion is
happening in megasamples, or gigasamples per second. Bandwidth is
expressed in Hz/MHz/GHz, and is literally the point at which the input
is attenuated by 3dB by the analog input circuitry feeding the A/D
conversion.

There is much more to say about scope specs, but there is good
literature on the manufacturer's sites.

I have noticed that Terry is using a Tek 3000 series (I think) from some
of his pics. I use a 3054 4 channel 5 Gs/s, 500 MHz unit for
portability. When safety and isolation are a bigger concern, I pull out
my Tek THS 730 handheld which has isolated channels (no common ground).
In the lab, or when I need blinding speed and/or stupid record length, I
use a Tek 7154B 4 channel which is 20 Gs/s and 1.5 Ghz. It's PC based
and has on board analysis of everything but your body temperature.

I would highly recommend that you read the primers that are on the
Tektronix site. Tek has a couple of solid competitors also(Agilent,
LeCroy, and others) but they publish some excellent articles on
oscilloscope technology.

Last but not least; if you want to go old school, save money, or just
simply don't need digital storage, the 1980's-1990's vintage Tektronix
analog scopes can be had for a steal on e-bay, and especially at the ham
swaps.

A 300 MHz Tek 2465 that went for over $10,000 new can be had for
$300-$500, and they are one of -the- analog scopes of choice. They were
standard issue for most of the armed forces for quite some time I
believe.

One last point of interest - a good Tek 2467 (for example) CRT scope can
actually briefly display single shot events that you will miss on a
digital at 3 times the price. They have a special amplifying CRT that
makes this possible. Once again, read the whitepapers on real time
sampling and record length. Also interesting, is that some of the high
energy physics labs still use this technology to write the waveform to a
diode array with the CRT, because it is faster than all but the most
esoteric digital hardware. (Tek used to sell a 250 GS/s digitizer based
on this approach).



Leigh






-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx] 
Sent: December 22, 2006 1:10 AM
To: tesla@xxxxxxxxxx
Subject: oscilloscope.. (fwd)

Original poster: Gerry Reynolds <greynolds@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Thu, 21 Dec 2006 19:14:23 -0500
From: Chip Ford <chipford@xxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: oscilloscope..

I am thinking of purchasing an oscilloscope. There are many out there
with many features..10mhz-1ghz. Digital, dual trace, analog..etc. seems
that the most common are @ 100 mhz, 2 channel. Most do not include
probes. These are not cheap so, If you-all would give me some advice on
buying a scope..or if someone has one in working order for sale...let me
know..Thanks in advance...Chip Ford