Re: TDS 420 Oscilloscope

Harvey White


I think it also depends on what bandwidth you need, and the repetition rate of the signals.

For a low bandwidth, once signal, you need either a storage oscilloscope (rare) or a digital scope.

For a high bandwidth scope, your required bandwidth has to do with the expected risetime of the signal you're trying to observe.

For a digital scope, assuming it can reproduce the same waveform, the "hold" (time that I can observe the waveform)  time is infinite.  For an analog storage scope, it is not.  On the other hand, the analog scope is analog, the digital scope is digital, and there *is* a difference in presentation AND capability.

For a non-storage analog scope, the faster the repetition rate, the brighter the trace.  For a digital scope, it simply doesn't matter.

The accuracy of the waveform is dependent on the sampling rate. Faster is better.  If you argue with the scope, it generally wins.

Digital scopes have strengths, analog scopes have others.

Digital scopes can do things analog scopes cannot do, but within the limits of digital sampling.  Analog scopes show things you can't see with digital scopes, but how easy that will be depends on the scope.  The 7103, 7104, and 2467 play very special tricks with the waveform displayed to show you information difficult to see on analog scopes.  That, and the bandiwidth, make those scope special.  The life of the CRT (opinions vary) makes them special purpose.

For a digital scope, what you're dealing with is the digitization rate (higher is better), channels (your opinion), and user interface.  User interface relates to the signal and what you can do once the signal is captured.  Your choice.


On 3/29/2020 12:53 PM, Siggi wrote:
On Sun, Mar 29, 2020 at 10:51 AM David DiGiacomo <daviddigiacomo@...>

If you must have a vintage DSO, I think an HP 54622A would be a good
On my bench I, in order of preference, I have a Tek 2467, a HP54622D and a
TDS784D. The 2467 is a joy to use, but when need to look at slow or
one-time signals, I go to the HP. Only if I run out of bandwidth do I ever
turn on the TDS scope.
So I'd second the suggestion of going for a HP54622X or similar in
preference to the TDS420.
The HP54600-series scopes drive pretty much like analog scopes, but have
long record capture, a good triggering suite and the -D versions come with
16 digital channels. In addition to the -22 and -24, which are 100MHz
bandwith, there exist 60, 350 and 500MHz variations (

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