> What specs should I look for when purchasing an oscilloscope for general use
> including Amateur radio?
"General use" is a broad concept. The natural response is "What do you want to
do with it?"
I use an o'scope for many things. I tune my RTTY signals using the X-Y
function on the scope. I look at signal levels of audio. I look at RF signals
at IF frequencies. I check P-P output and convert to RMS using the scope. I
inject time delays to zero in on a waveform that is delayed from the trigger
waveform. Looking at binary signal timing is beneficial in many circumstances,
so more than two inputs may be important to you. You can check keying
waveforms of CW. Use it as a DC voltmeter if you want. In all these
functions, bandwidth is important to what you intend to do. If it's audio, you
can use some pretty simple scopes. If you are looking at RF, obviously the
bandwidth has to be sufficient to have a calibrated output on the screen.
If you want to just look at waveforms, and not absolute timing of same, a
pretty simple indicator may be sufficient. Likewise, if you need to look at
logic levels and determine accurate time periods, you will need a calibrated
scope with sufficient accuracy to do what you want to do. By calibrated, the
gradients on the screen are calibrated to the settings of the horizontal and
vertical amplifiers in the scope. Looking at wave form edges down to 1 ns or 2
ns is no real trick with a decent scope. Doing it accurately takes proper
probes and proper setup of the test.
A 100mHz scope can be usable beyond 100mhz, but the gradients will no longer be
calibrated. In fact, without proper probes, terminations, and test
configuration, the results will be wildly out-of-line with reality. One can be
had for a couple hundred bucks on the used market.
If you want to automate your tests, and convert time to frequency, P-P to RMS,
and digitally display the results, you spend more money. If you want to
connect your scope to a computer, you will spend more yet. Screen capture,
displaying the setup parameters and such, all are extra money and extra nice.
Bang for the buck as they say.
My 4 bay Tech 7704A scope frame actually has a handle on the top of it, but I
would hardly call it a portable. Plug-ins are pretty reasonable at maybe $50
to $150 each, depending on function. Plug-ins can include spectrum analyzers
too. So one frame can serve multi-purposes. (time domain vs frequency domain)
Digital vs analog is another option that can prove very valuable. Wave form
filtering may be important to you. Selectable bandwidths can be handy.
Form a budget for what it's worth to you, and go buy one. There are hundreds
of styles and functions. But they all display in the time domain. So it
really depends on what you intend to do with it. If you want one that does
everything, plan on $10K or more, and even then there will always be better
available.
Ford-N0FP
ford@cmgate.com
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