Hot Rod Oscilloscope
by Dennis L. Feucht
Innovatia Laboratories
With apologies to the '60s hit tune, "Hot
Rod Lincoln"
(In the mood to sing along? Our web search found one recent cover of the
tune here...)
You've heard the story of the bandwidth race,
Where 'scopes and counters were setting the pace;
Well that story is true, I'm here to say;
I was using a 545A.
It's got a graticule, all lit up,
That front-panel claptrap makes it look tough.
It's got plug-ins, uses 'em all;
It's got good risetime, and also fall.
With a dual-trace display at reasonable cost,
And forty-eleven knobs, you can really get lost;
It's got a dual-delayed timebase, but I ain't scared,
The trace is sharp; the probes are fair.
Pulled out a new project late one night,
The test equipment was burning bright,
I started driving a wideband amp,
To see which stage I needed to damp.
When all of a sudden in the blink of an eye,
A series of waveforms passed me by,
And I said, "Wow, that's a marvel to me!"
Pretty soon a square-wave was all I could see.
Now the boss was ribbing me for being behind,
So I thought I'd make the probes unwind,
Took the volts per div knob, and man alive!
I turned it up to a setting of 5.
Powered the wideband amp again,
And drove it with a function gen,
Set the amplitude knob to three or four,
The levels were hitting the ceiling and floor.
Now the transient response made no sense,
The scope display looked like a picket fence.
I slowed it down and was glad to know,
That it wouldn't alias like a DSO.
I tweaked the circuit here and there,
Replaced a cap and transistor pair;
Got the speed I needed with room to go;
Manufacturing would be glad to know.
Smoke was coming from out of the load
When I set the trigger to hf mode;
The power bandwidth was looking right;
Nearly approaching the speed of light.
The task was finished, the specs first-rate,
The customers called, said the amp worked great;
I got a promotion, moved out of L.A.,
And I credit success to that '45A!
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