Help me test this function generator

[openthomas]

Picked up a smartarb 625A. Trying to figure out if it is working OK, got it cheap. I hooked it up to my oscilloscope played around a bit ( see video at 2:04 ). I noticed that the frequency of the wave jumps around a bit. Is that normal ?



How should I go about testing this thing ?

[MasterOfNone]

What you are seeing might be normal, the frequency counter feature on your scope isn’t going to be as accurate as a dedicated Frequency counter. 
If you think the Frequency is really jumping around then don’t look at the trigger position on the scope. What you should do is adjust the Horizon position so that you are looking at the waves a lot later than the trigger position (I.e. the trigger position disappears off to the left of the screen). Then set the display to Infinite Persist. With your scope setup like this any frequency changes between the trigger position and the position displayed on the scope will cause the waveform to be drawn in a different position on the screen, and since the scope is set to infinite persistence you will see it.   So you can leave the system running like this for a while and if the frequency is really jumping you should catch it.
Remember you can test the principle by manually changing the Frequency of your function generator by a small amount temporally.

[openthomas]

Ok I think I got that, take a look

[MasterOfNone]

That only looks like a bit of jitter to me.  If the frequency was jumping temperately I would expect to see the wave drawn in a completely different place on the scope.  However when doing the test I see that you have only move the horizontal position along 56.56us. If you moved the horizontal position further along you would have more of a chance of catching the problem on the scope, because every time the scope triggers there would be less of the capture to the right of the point you are viewing.

But anyway the Frequency displayed on my DS1052E does the same thing as yours, but when I use my dedicated Frequency Counter I don’t see this issue.