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Oscilloscope probe ground leads act as FM attennea
tautech:
I can get 100's on mV doing the same under LED lighting....this is only the additional sensitivity a DSO can provide.
Trick is to know what it is and where from so to not focus on it and only on the part of the signal that matters.
20 MHz BW limit is very useful at times.
ebastler:
As Martin said, the frequency range almost exactly matches the FM band (at least as defined in this part of the world, 87.5 to 108 MHz). And in your later post the signal does look modulated, although it looks more like AM modulation -- is that being used in this frequency range in Canada?
If you can visit a friend out of town, further away from the transmitters, it's something I would try to get a better understanding and confirm the radio interference theory.
Also -- does the noise appear specifically when you measure the calibration signal? What happens when you just ground the probe tip (clipping the probe's little ground lead to it)? What happens if you do the same, but grounding via e.g. a 100 kOhm resistor? If it should just be the 1 kHz reference output that catches the radio interference, that would be odd but would not affect your use of the scope.
dmulligan:
--- Quote from: tautech on October 29, 2023, 10:05:35 pm ---I can get 100's on mV doing the same under LED lighting....this is only the additional sensitivity a DSO can provide.
Trick is to know what it is and where from so to not focus on it and only on the part of the signal that matters.
20 MHz BW limit is very useful at times.
--- End quote ---
Agreed. I am trying to determine the sources of the noise I am seeing in my work area. I was amused at and wanted to share the large commercial FM broadcast interference I am seeing, that or asking for advice about how I am measuring incorrectly. Sadly I am having trouble narrowing down just what it is if it isn't the FM broadcasts. It's not in this room and I've been waiting for a time that I can shut down the entire house and bring it back up one breaker at a time.
Fungus:
--- Quote from: ebastler on October 29, 2023, 10:09:12 pm ---If you can visit a friend out of town, further away from the transmitters, it's something I would try to get a better understanding and confirm the radio interference theory.
--- End quote ---
Get a battery and go for a drive...
tautech:
--- Quote from: dmulligan on October 29, 2023, 10:24:43 pm ---
--- Quote from: tautech on October 29, 2023, 10:05:35 pm ---I can get 100's on mV doing the same under LED lighting....this is only the additional sensitivity a DSO can provide.
Trick is to know what it is and where from so to not focus on it and only on the part of the signal that matters.
20 MHz BW limit is very useful at times.
--- End quote ---
Agreed. I am trying to determine the sources of the noise I am seeing in my work area. I was amused at and wanted to share the large commercial FM broadcast interference I am seeing, that or asking for advice about how I am measuring incorrectly. Sadly I am having trouble narrowing down just what it is if it isn't the FM broadcasts. It's not in this room and I've been waiting for a time that I can shut down the entire house and bring it back up one breaker at a time.
--- End quote ---
Your FFT clearly shows peaks at each FM station.
Engage Peak markers and compare results to published local FM frequencies.
We had a customer that was convinced his new SDS1104X-E was broken but after assurance it wasn't he eventually found a unknown wallwart behind a curtain across the room. Some of these things just spew EMI.
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