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Old 6th February 2011, 06:25 PM   #1
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Default oscilloscope defect (?) horizontal more intense than vertical

I'm considering buying a used oscilloscope from the estate of an old HAM radio guy who died. I'm not very familiar with analog oscilloscopes; it's been decades since I played with them in school.

So I was wondering if the issue I noticed with this one is normal. Please see the picture in the attachment. What I found was that when viewing the calibration square wave, the horizontal lines were much more intense than the vertical lines, so much so that the vertical lines were hard to see.

I don't see this issue with my new digital storage oscilloscope, of course. Can anyone comment whether it would be possible to make the horizontal lines more visible through calibration, or adjustment of front panel controls, or is this something where different models perform differently?

I definitely know I've seen analog scopes displaying square waves where the horizontal and vertical lines are equally intense... perhaps this requires circuitry in the oscilloscope to change the intensity depending on the rate of deflection, and this scope has issues (or is missing) that circuitry?
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Old 6th February 2011, 06:30 PM   #2
Wayniac is offline Wayniac  United States
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Looks normal to me.......(30 years experience).
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Old 6th February 2011, 08:08 PM   #3
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Just as it should be. I'd be a bit concerned if a digital scope showed strong vertical lines with a fast rise or fall square wave.

CH
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Old 6th February 2011, 08:30 PM   #4
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by perfknee View Post

I definitely know I've seen analog scopes displaying square waves where the horizontal and vertical lines are equally intense... perhaps this requires circuitry in the oscilloscope to change the intensity depending on the rate of deflection,
There is sometimes a Z-modulation wrt to spot speed, but this can only work between limits obviously.
Anyway, this is one of the "features" of analog scopes: it is one of the many clues they give on a signal in addition to the waveform shape itself.
Digital scopes try to imitate it with DPO and similar tricks, but they are only moderately convincing compared to the real thing.
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Old 7th February 2011, 03:14 PM   #5
macboy is offline macboy  Canada
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No fear; this is just due to the way analog scopes create the image you see.
The scope sweeps the electron beam from left to right at a specified rate (depending on the setting of your time/div dial). The vertical deflection is controlled by the input signal. So when the signal transitions in level very quickly, such as the edge of a square wave, the trace moves so quickly that hardly any electrons hit that part of the screen, so it doesn't glow much.
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Old 8th February 2011, 12:53 AM   #6
Enzo is offline Enzo  United States
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What he just said.

The test signal is a square wave, the signal voltage snaps instantly from the higher to the lower voltage and back. So there is no vertical line to display, really, unless you really speed up th sweep.

COnnect it to a sine wave or music, or just touch the probe tip with your finger, and you should see a nice bright trace.
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Old 8th February 2011, 08:00 AM   #7
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That Philips PM 3212 was a nice scope, mine had a measured bandwidth of 35Mhz as opposed to the sprc of 25Mhz.

Barry
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