Rigol DG1022 square wave issues

[ticktock3t]

I recently scored a Rigol DG1022 off ebay for $220. I like everything about it but when I was testing it out I noticed something very strange with its square wave output. At the lower end frequencies it outputs a nice square wave but when I crank it up to 5MHz the signal doesn't even look like a square wave anymore. It become highly distorted with a large overshoot. Should I just accept this or should I send this back to the seller.

[PA0PBZ]

It could be the way you are measuring it 

[PA4TIM]

To see the true  5 MHz squarewave you must terminate the generator in 50 Ohm at the scope and use a scope that is at least 50MHz.
So what scope you use and how you connect the generator to the scope.

Also look in the manul from the Arigol what it's Tr and Tf is at 5 MHz.

[ticktock3t]

Even at the lower frequencies I can still see, when I zoom into the square wave, an overshoot so could this be a problem with the function generator?

[alm]

To repeat what Fred said: does terminating the function generator into 50 ohms help?

[bernie]

Here's the output from my DG1022, 50 Ohm terminated at both scope and function gen (utility menu), link directly with coax.
The second is with scope and generator on High Z
Seems passable, but is at it's 5MHz limit

Hope the screenshots help

[kg4arn]

It looks to me like there is less than 5% overshoot, which is within the spec on the datasheet.

[ticktock3t]

I somewhat get the same image that Bernie has posted, but as you can see the signal is not clean at all. Is that normal? Also, How come this distortion only applies to the square wave and not to the other waves. I have heard of square waves overshooting before. I'm going to upload some pictures from my oscilloscope soon.

[alm]

The manual lists the allowed aberrations in the square wave output. Rise / fall time is < 20 ns typical from 10% to 90%, so a typical DG1022 will take up to 20 ns to rise from 10% the output amplitude to 90%. Overshoot is < 5% typical, so on a rising edge a typical DG1022 will overshoot the high level by 5% of the amplitude. Note that none of these are guaranteed specs.

Edges of square waves contain more high frequency content than for example sines with the same period, so imperfections in both function gen and cable are much more noticeable (hence the difference between high impedance and properly terminated scope input). For square waves the bandwidth depends on the rise time, not on the repetition rate. Sine waves (ideally) contain just one frequency, so an imperfect frequency response will only change the amplitude flatness. The human eye also sucks at visually detecting distortion in sine waves.

[flolic]

Same setup as bernie's (high Z) on my DS1102E scope:

[ticktock3t]

Does anyone else find this much distortion strange? It doesn't even look like a square wave anymore.

[robrenz]

My DG1022 with inline 50 Ohm termination into rigol 1052E
First is 5V PP at 5M
Second is 10V PP at 5M

[w2aew]

Does anyone else find this much distortion strange? It doesn't even look like a square wave anymore.

Not really.  Depends entirely on the speed/bandwidth of the generator and the scope, as well as the quality of the coax cable and the termination.  In this case, the generator spec states that the max square wave frequency is only 5 MHz. So, it is NOT going to look ideal anymore at the max rated output speed.  Compared to other wave shapes, a square wave places the largest demand on the speed/BW on the output buffer.  Bottom line, looks like I'd expect for a generator that's only rated for a 5 MHz square wave.
http://www.rigolna.com/products/waveform-generators/dg1000/dg1022/