CS328A-XSEi noise floor measurement
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daehee-kim
27th February
Posts: 1
I have two CS328A-XSEi units that I want to measure the noise floor of.
Using a copper wire, I shorted the BNC inputs of both channels.
The sampling rate was 20kHz and the measurement time was 5ks.
I have attached the power spectral density of the measurements, including the two units and the channels A and B.
As you can see, Cleverscope 2 shows a flat noise floor for both channels, whereas Cleverscope 1 shows a rising noise floor.
While I only attached one set of measurements, I have also observed a rising noise floor in Cleverscope 2.
Also, it would be great if you could comment on the origin of the harmonics observed in the noise peaks, as I am a beginner.
Thank you very much.
Using a copper wire, I shorted the BNC inputs of both channels.
The sampling rate was 20kHz and the measurement time was 5ks.
I have attached the power spectral density of the measurements, including the two units and the channels A and B.
As you can see, Cleverscope 2 shows a flat noise floor for both channels, whereas Cleverscope 1 shows a rising noise floor.
While I only attached one set of measurements, I have also observed a rising noise floor in Cleverscope 2.
Also, it would be great if you could comment on the origin of the harmonics observed in the noise peaks, as I am a beginner.
Thank you very much.
bartschroder
6th March
Posts: 503
Hi Daehee-kim,
thanks for the question. Unfortunately this is not a very good way to measure the noise floor. I attach a document 'CS328A Noise Floor', that describes what I found with the CS328A sitting on my shelf. I see some artifacts I had not expected, but they are small.
Answering your post:
1. It is not good to short the input with copper wire. This will make an antenna which will pick up all the local radio stations, which will alias into the displayed spectral frequency range. It is better to have the inputs open, or to short with a 50 Ohm BNC terminator. Open is easiest.
2. I don't see much point in sampling so slowly, for so long. First any higher frequency alias products will alias back into the displayed FFT. Secondly there is a better way! Use the built in Spectrum Analyser and use that to display the noise floor. The document shows how.
I hope this helps.
Bart
The file has been renamed so it can be downloaded
thanks for the question. Unfortunately this is not a very good way to measure the noise floor. I attach a document 'CS328A Noise Floor', that describes what I found with the CS328A sitting on my shelf. I see some artifacts I had not expected, but they are small.
Answering your post:
1. It is not good to short the input with copper wire. This will make an antenna which will pick up all the local radio stations, which will alias into the displayed spectral frequency range. It is better to have the inputs open, or to short with a 50 Ohm BNC terminator. Open is easiest.
2. I don't see much point in sampling so slowly, for so long. First any higher frequency alias products will alias back into the displayed FFT. Secondly there is a better way! Use the built in Spectrum Analyser and use that to display the noise floor. The document shows how.
I hope this helps.
Bart
The file has been renamed so it can be downloaded
Attached Files
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