I just got my 2nd oscilloscope from eBay. If you recall the first had a problem with what looked like noise at the tops an bottoms of the calibration sq, wave on the first one that I purchased (since returned). Plus the first scope had no vertical deflection, when touched to a battery, when set to DC coupling and I could not adjust the probe for a good sq wave on channel 2 (probably related to the no DC deflection problem).
Anyway I got the new scope and I am afraid that I am seeing some of the same problems but not sure. I am getting a good square wave on both channels. And I get deflection from both channels on DC coupling when hooked to a battery. This scope is a Tek 475A with DMM option. Of course it is an analog scope.
But I am still seeing what looks like noise at the tops and bottoms of the waves when using a 10X probe under certain conditions.
There is a control on the scope called Vert Mode / 100 or 20MHZ BW.
The manual says that this switch limits the bandwidth of the vertical amp.
Here is what I found with that setting. All tests were done with vertical deflection set to 5MV / division and the probe attached to the calibration port.
If I set the limit to 20MHZ and the probe to 10X I see a good clean wave form. A nice crisp line at the tops and bottoms of the square wave.
If I change the probe to 1X, I can see what looks like small spikes crawling on the tops and bottoms of the square waves. They are 1 mv at best but they are there. I noticed that I also see these crawling spikes when I touch the probe while it is attached to the calibration port.
If I change the BW limit to 100MHZ I and 1X probe, I can see the "crawling spikes" around 5MV with the 1X probe. The noise is still there with the 10X but not nearly as bad. On the scale it is maybe 3mv but of course tnat is really divided by 10.
I see a similar behavior on the "unlimited" bandwidth setting.
I see a similar behavior when attached to the
Trace looks nice and clean on all settings when probe is grounded.
Is this normal? Maybe it is just a case of cheap probes? If it was line noise (power supply), shouldn't I see it on the 20 MHZ limit setting?
Maybe it is my nearby PC (10feet) away). I will shut down everything except for the the scope and post back after I submit this.
Other questions.
How easily should I be able to see the rising and falling traces of the square wave. I can barely see them. I have to jack up the intensity pretty far to see them. I cannot remember, is this normal for analog scopes?
Should I be able to sync on Line trigger? I don't seem to be able to do it when the probe is attached to the cal port. The sq wave keeps scrolling no matter how I adjust the trigger level. I can get it to slow a bit but that is about it.
Anyway I got the new scope and I am afraid that I am seeing some of the same problems but not sure. I am getting a good square wave on both channels. And I get deflection from both channels on DC coupling when hooked to a battery. This scope is a Tek 475A with DMM option. Of course it is an analog scope.
But I am still seeing what looks like noise at the tops and bottoms of the waves when using a 10X probe under certain conditions.
There is a control on the scope called Vert Mode / 100 or 20MHZ BW.
The manual says that this switch limits the bandwidth of the vertical amp.
Here is what I found with that setting. All tests were done with vertical deflection set to 5MV / division and the probe attached to the calibration port.
If I set the limit to 20MHZ and the probe to 10X I see a good clean wave form. A nice crisp line at the tops and bottoms of the square wave.
If I change the probe to 1X, I can see what looks like small spikes crawling on the tops and bottoms of the square waves. They are 1 mv at best but they are there. I noticed that I also see these crawling spikes when I touch the probe while it is attached to the calibration port.
If I change the BW limit to 100MHZ I and 1X probe, I can see the "crawling spikes" around 5MV with the 1X probe. The noise is still there with the 10X but not nearly as bad. On the scale it is maybe 3mv but of course tnat is really divided by 10.
I see a similar behavior on the "unlimited" bandwidth setting.
I see a similar behavior when attached to the
Trace looks nice and clean on all settings when probe is grounded.
Is this normal? Maybe it is just a case of cheap probes? If it was line noise (power supply), shouldn't I see it on the 20 MHZ limit setting?
Maybe it is my nearby PC (10feet) away). I will shut down everything except for the the scope and post back after I submit this.
Other questions.
How easily should I be able to see the rising and falling traces of the square wave. I can barely see them. I have to jack up the intensity pretty far to see them. I cannot remember, is this normal for analog scopes?
Should I be able to sync on Line trigger? I don't seem to be able to do it when the probe is attached to the cal port. The sq wave keeps scrolling no matter how I adjust the trigger level. I can get it to slow a bit but that is about it.