Why Is My Oscilloscope Signal Pulsating?

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Discussion Overview

The discussion revolves around the issue of a pulsating signal observed on an oscilloscope while measuring with a pulsed laser. Participants explore potential causes for the instability in the signal, considering both equipment-related issues and external interference.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant describes the problem of a pulsating signal, noting that the baseline jumps up and down, and suggests that disturbances from nearby work might be a factor.
  • Another participant requests additional information, asking for pictures of the setup and a schematic to better understand the situation.
  • One suggestion is to check the photodiode or amplifier, with a recommendation to test with a replacement if available.
  • Some participants propose that the pulsating signal could be due to interference from a nearby radio transmitter, such as a paging transmitter.
  • A later reply supports the interference theory, mentioning that removing averaging revealed a detectable signal at intervals.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the cause of the pulsating signal, with suggestions ranging from equipment issues to external interference. No consensus is reached on the definitive cause.

Contextual Notes

Participants have not provided specific details about the setup or the conditions under which the measurements are taken, which may limit the analysis of the problem.

nordmoon
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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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