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zero dB offset

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zero dB offset

Postby Jeremy » Sat Nov 01, 2003 2:15 pm

I am using the zero-dB level to offset the zerodB setting in the INI file.

I need the offset both to convert to spectral density function (noise/Hz) but also for phase noise measurement calibration. I need to offset up to 80 to 100dB (ie 10 to power 4 or 10 to power 5 in volts).

Is there a maximum number for this. I managed to get the measurement at the bottow of the scale to -160dB but need a little lower. I don't need resolution I just need more powers of 10 (eg 1.8E9) and it seems to ignore more beyond a certain limit. The problem is that it is in microvolts which immediately adds 10 to the power 6 and it does not seem to allow one to add more than around 10 to the power 8 or 9. Is there an exponent form to express the number of zeros ( ie 1.8E9)?

Also should the zero dB reading be the same when nothing is added in the ini file and when 10 to the 6 is added. They seem slightly different. Is this an rms to peak conversion?

Has the number of samples when using 4096 been corrected yet. ref my last post.

Many thanks


Postby markspencer » Tue Nov 04, 2003 8:29 am


There is a limit on the ZeroDb value this is (2^31)-1, 2147483647, this is due to the variable being declared as a long. This means that you can get as low as -180dB when the voltage range of ±50mV is selected.

The reference value that picolog uses is 776000 microvolts, so you will not get the same when no value is entered and when 1,000,000 is given to the value of zeroDb.

We are still investigating the average problem.

Best regards,

Mark Spencer
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