EEVblog Electronics Community Forum

Products => Test Equipment => Topic started by: klaus1311 on May 16, 2015, 11:43:52 am

Title: Keysight X2014 strange display
Post by: klaus1311 on May 16, 2015, 11:43:52 am
Hello,

this is my first post in this forum. My name is Klaus and I'm living in Germany Bavaria.
I've been playing with my KeySight InfiniiVision X2014. I got a signal shown, I can't explain myself. Perhaps someone from the forum can. If I switch off "math", the signal looks normal. But in the background it still looks slightly modulated.

My Settings:
Loop from WaveGen to Channel1
WaveGen:
Squarewave  5MHz, 1V PP, Offset 0, Dutycycle 50% Output Load 50Ohm, Add Noise 0%
Channel1:
Coupling DC, Noise Reject None, HF_Reject None, Holdoff 40usNormal Mode

Firmware Version 2.39

Klaus
Title: Re: Keysight X2014 strange display
Post by: tom66 on May 16, 2015, 11:56:24 am
Could be an aliasing effect. The math function may be causing the unit to slow down the processing or sample rate causing the aliasing to happen when it otherwise would not normally happen.
Title: Re: Keysight X2014 strange display
Post by: AndyC_772 on May 16, 2015, 12:08:09 pm
You're sampling a 5 MHz square wave at 10 MHz. Maybe the WaveGen clock and the sampling clock aren't synchronised?
Title: Re: Keysight X2014 strange display
Post by: 0xdeadbeef on May 16, 2015, 12:28:23 pm
What does "BW" mean? Maybe bandwidth limit on?
Title: Re: Keysight X2014 strange display
Post by: dom0 on May 16, 2015, 01:49:02 pm
Sampling a 5 MHz square wave with 10 MHz is bound to alias.
Title: Re: Keysight X2014 strange display
Post by: MarkL on May 16, 2015, 04:06:47 pm
It is aliasing.  The 2000X and 3000X scopes turn off anti-alias dithering when certain math functions are turned on, such as FFT.

Discussed previously:

  https://www.eevblog.com/forum/testgear/agilent-dsox-2000-aliasing/msg569835/#msg569835 (https://www.eevblog.com/forum/testgear/agilent-dsox-2000-aliasing/msg569835/#msg569835)
Title: Re: Keysight X2014 strange display
Post by: Hydrawerk on May 17, 2015, 05:50:23 pm
Quote from: 0xdeadbeef on May 16, 2015, 12:28:23 pm
What does "BW" mean? Maybe bandwidth limit on?
Yes. When bandwidth limit is on, the maximum bandwidth for the channel is
approximately 20 MHz.