Scopes for Hams

On the Elecraft mailling list, Doug KØDXV wrote:

I am interested in learning about oscilloscopes and how to use them. I would like to learn how to trace and debug digital as well as analog radio circuits. Any recommendations on a good used scope? Any thoughts on any books that might provide a useful overview of using a scope to debug RF and digital problems?

Don W3FPR, the Elecraft guru, replied:

Paul Harden N5AN has written good articles on the use of the oscilloscope. One can be found in text format in the QRP-L archives.

If you are doing nothing but observing RF voltages with your ‘scope you
might be able to get by with your 20 MHz ‘scope, but I recommend a 100 MHz
scope.

To make good use of the ‘scope without loading the circuit under test, you
will need some good 10X scope probes. The probes have a frequency rating
too and should be rated for 100 MHz or higher for use in the HF ham band
region.

Regarding frequency ratings of probes and ‘scopes – the rated frequency is
the point where the response drops off by 3 dB, so 100 MHz will provide good
calibrated readings at 1/10th of the frequency rating and is quite usable up
to 1/3 the frequency rating. In other words, the response of a 100 MHz
‘scope will be quite accurate through 10 MHz and reasonably accurate at 30
MHz, but will drop off significantly above 30 MHz. You will still be able
to use the ‘scope up to its frequency limit (and maybe above), but you
should not trust the voltage measurements made with it at those limits (the
waveforms may show some distortion at the limits too).

As for buying an oscilloscope, I highly recommend purchasing one from Bob
Garcia. He is known as ‘Mr. Scope’ and frequents many of the hamfests in
the Southeast (he lives in GA). I have recently have had dealings with him
and can say that he is more than fair both in price and his manner of doing
business. You can email him at mailto:[email protected] and ask him
what he has available.

Dave G4AON added:

I’m not sure about books to describe how to use a scope, there isn’t much to using one and there’s plenty of information on the web, see Chapter 4P of the online book Design Electronics by W.D. Phillips as an example.