search

usnistgov / SpectrumBrowser

ITL
12 stars 11 forks source link

dBm/nHz --> dBm/Hz calculation #109

Open MichaelCotton opened 9 years ago

MichaelCotton commented 9 years ago

dBm/Hz is calculated as dBm/Hz = dBm/nHz - 10log10(nHz), so for a threshold of -90 dBm in a 1 MHz RBW translates to:

-90 dBm/1MHz - 10log10(1MHz) = -90 - 60 dBm/Hz = -150 dBm/Hz

ranganathanm commented 9 years ago

More clarification needed. The computation above indicates that the threshold is specified in dBm/MHz but the result is in dBm/Hz. Did you mean dBm/MHz on the rhs of the example?

Let be X is the quantity entered in the threshold page in dBm/Hz then :

actual threshold for occupancy computations = (X - 10log10(RBW))*(RBW) dBm

It might be useful to display this quantity on the GUI because it is quite counter intuitive.

msouryal commented 9 years ago

What Mike wrote is correct. The term -10log10(1e6) converts from dBm/MHz to dBm/Hz.

To summarize, the threshold density (in dBm/Hz) is computed as

X_d = X - 10log10(RBW)

where the RBW is in Hz and X is the absolute threshold in dBm.

To compute the actual threshold for occupancy computations, do the reverse:

threshold for occupancy computations = X_d + 10log10(RBW) = X dBm

MichaelCotton commented 9 years ago

Also, "*(thresholdMaxFreq - thresholdMinFreq)" should not be in the eqn. Only use thresholdMaxFreq and thresholdMinFreq as integration (or summation) bounds, when summing over the frequencies and dividing by N to calculate occupancy.

ranganathanm commented 9 years ago

Just to be sure then, the admin will enter X_d in the "Add threshold" GUI. I can put up an alert indicating the occupancy calculation threshold in this GUI. Also, we spoke today about being able to edit the fields of the threshold. Because ( Sys2Detect, thresholdMinfreq, thresholdMaxFreq ) is the key, we cannot allow edits on that but we can allow edits on X_d.

ranganathanm commented 9 years ago

This has been implemented. Please test the admin pages.