Magnus & Mark, for my Thunderbolt system I found a very good correlation between AMU and dBc/ Hz ( observed on my system using the ThunderboltMonitor watching over long time stable satellite signals ) when I use the Formula: C/N0(dBHz) = 20 log(AMU) + 23.5.
73, Arnold On Sat, 13 Feb 2010 18:12:52 +0100, Magnus Danielson wrote: >Mark Sims wrote: >> The data was collected in 0.1 dB / AMU steps. There was a lot of noise in >> the raw data (maybe +/- 1 dB or AMU), but the general trend of the curve >> was quite distinct. I smoothed it out by hand and filled in a few (maybe >> 15) of the missing steps that had no signal. >> >> The 0.1 resolution of the raw data causes the piecewise linear steps in the >> data. I was going to run a smoothing filter over it, but the curve is >> pretty good as-is (especially considering how it was generated). >> >> Heather now uses a table lookup from 0.0 to 25.5 AMU with a linear >> approximation over 25.5 AMU to convert AMU values to dBc values when drawing >> the signal level map if the receiver is in AMU mode. The plots collected in >> AMU mode and dBc mode are virtually indistinguishable (within the normal >> variation seen between two different runs in dBc mode). >> >My current speculation is this: >It looks like the AMU unit is normalized and biased such that AMU value >0.0 is a reasonable border limit of 20 dBc. >Thus, from the correlated amplitude A I think the AMU is calculated like >this: >AMU = A/A_norm - A_bias >A_norm scales linearly with sample-rate of digital sampling. >A_bias adjusts such that A relating to 20 dBc gives the AMU of 0.0. >The dBc calculation is more straightforward: >dBc = 20*log(A/A_norm) + dB_offset >A_bias of 0.6 to 0.7 and dB_offset of 22.6 isn't too far off. >Cheers, >Magnus >_______________________________________________ >time-nuts mailing list -- time-nuts@febo.com >To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
