Helicopter data set a20mc1

Helicopter excursion A, collected at 20MHz, channel 1. For a description of how this data was collected, go back to Helicopter Data, Excursion A.

[H2Dot] Graphs

Click on the thumbnail sketch to see the full-sized plot.

[time plot] plot first 256k samples of data, (0-14 ms).

[freq plot] plot power spectral density, (DC-10MHz, semilog).

[freq plot] plot power spectral density, (DC-10MHz, loglog).

[H2Dot] Analyses

Most of the content is obviously below 50kHz. Much of what remains is undoubtedly quantization noise.

Suppose we calculate the power spectral density, (PSD), we would expect due to quantization noise alone. Let w denote the quantization noise process, with Fourier transform W, and power spectral density P. I estimated P by averaging |W|^2 over 244 successive segments of size L=4k, then dividing by L^2. The oscilloscope was set to 50mV/div on this channel, so the quantization step size, given 8-bit resolution, is q= (50e-3V/div)*(8div)/(2^8)=1.5625e-3V. So w is uniformly distributed over (-q/2, +q/2), and its variance is (approximately) s=2e-7 (V^2). Assuming the quantization noise samples are uncorrelated, the expected value of |W|^2 is L*(s^2), so the expected value of the PSD is P=(s^2)/L=5e-11, (for all frequencies). This compares very well with the noise floor, (roughly horizontal, with values between 5e-11 and 7e-11), observed in the plotted PSDs.