General Oscilloscope Question

Jun 22, 2008 5 Replies

I recently purchased an oscilloscope on Ebay. It is a 100Mhz model. I was configuring the scope using the calibration output, which is a



1Khz 2 volt square wave. The horizontal line drawing on the scope looks good, however, the vertical trace portion on this wave is barely visible at the highest brightness setting. Is the normal, or is there a problem with the scope? Is this common with analog scopes? This is my first oscilloscope, so I=92m not sure. Here=92s a photo I took. Any ideas?

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Thanks.


That's exactly how it should look (although I would turn the brightness down a bit). The amount of time the trace spends on the vertical part of the trace is small (the beam is moving very fast) relative to the horizontal part, so it's dimmer.

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That's normal for an analog display, the raise time of the square wave is so good that it's not allowing the beam in the CRT to stay on a section long enough to fully charge the phosphorus.

You'll find other signals that are not raising so fast like your test signal and the vertical line will be more visible..

You can make adjustments to the settings of the CRT controls to help you a bit on the visibility of the line. Making it brighter is not the answer.. If the scope has a LP (Low Pass) filter option, you may want to try that. It will remove some of the square corners from the wave how ever, it should improve on the visible problem.

A digital scope with LCD won't react like that.

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"

1Khz 2 volt square wave. The horizontal line drawing on the scope looks good, however, the vertical trace portion on this wave is barely visible at the highest brightness setting. Is the normal, or is there a problem with the scope? Is this common with analog scopes? This is my first oscilloscope, so I?m not sure. Here?s a photo I took. Any ideas?

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Thanks.

That looks more or less normal but to be on the safe side, turn down the brightness so you don't burn holes in the phosphor and select a slow sweep speed so you can easily follow the spot as it crosses the screen and adjust the astigmatism (Astig) until the spot is as near to perfectly round as you can get it.

It's just making the transition from 0V to 2V almost instantaneously (high slew rate). Leaving little time for the phosphor on the screen to respond. It looks like it's responding well.

That part has always bothered me. I have a 1990 vintage 4 channel,

100MHz, 2245 with only about 40 hours of use after 18 years, and it has the same square wave. Having a 1KHz and a 1MHz calibration would have been appreciated so the rise time could be checked for overshoot and proper probe calibration for higher frequencies. That part aside, it works like a dream since 99% of my needs are below 100MHz. It was bought for me by a company I was consulting for so I could do more work at home and not have to be physically in their building, but I had to pay 'income' tax on it. I would still like to get an older 547 since that had the sharpest display of any scope, ever. Bill Baka

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