Why Is My Oscilloscope Signal Pulsating?

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The discussion revolves around a user experiencing pulsating signals on their oscilloscope while measuring with a pulsed laser. The signal, previously stable, began to show fluctuations in its baseline, potentially due to nearby disturbances. Suggestions include checking the photodiode and amplifier, as well as considering interference from nearby radio transmitters. The user noted that removing averaging revealed a detectable signal at intervals. The issue appears to be linked to external interference affecting the oscilloscope readings.
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Hi, so i am doing measurements with a pulsed laser using an oscilliscope.

The signal has been ok (stable) until this afternoon when I noticed the signal started pulsating. The baseline of the signal suddenly jumps up and the baseline becomes larger, and then go down to normal.. and it keeps "pulsating" like this. Any idea what could be wrong? There might be some disturbances from other work nearby, but I am unsure what it could be.
 
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nordmoon said:
Hi, so i am doing measurements with a pulsed laser using an oscilliscope.

The signal has been ok (stable) until this afternoon when I noticed the signal started pulsating. The baseline of the signal suddenly jumps up and the baseline becomes larger, and then go down to normal.. and it keeps "pulsating" like this. Any idea what could be wrong? There might be some disturbances from other work nearby, but I am unsure what it could be.
Could you use the UPLOAD button to post pictures of your setup and show us your schematic?
 
One thing to check would be the photodiode/amplifier. If you have a replacement, try testing with a different one.
 
It looks like interference from a nearby radio transmitter going on and off, such as a paging transmitter.
 
tech99 said:
It looks like interference from a nearby radio transmitter going on and off, such as a paging transmitter.

I agree, when i removed the averaging I could see that there was a signal detected at some interval by the LPD3 tube.
 

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