On 26 Sep 2014 13:01, "Andrea Baldoni" <[email protected]> wrote: > > On Fri, Sep 26, 2014 at 10:07:56AM +0100, Dr. David Kirkby (Kirkby Microwave Ltd) wrote: > > > I don't understand the units of signal strength > > > > "The L1 carrier is spread over a 2 MHz bandwidth and its strength at the > > Earth's surface is -130 dBm. Thermal noise power in the same bandwidth is > > -111 dBm" > > > > Then goes on to talk about the signal being 20 dB below the noise. > > Hello David. > > It could be because there is a "process gain" associated in demodulating a > spread spectrum signal. > > Best regards, > Andrea Baldoni
But fundamentally to say "its strength at the Earth's surface is -130 dBm" makes no sense, UNLESS the author is trying to say that the earth receives a signal of -130 dBm if you add up all the powers over every square metre of the earth, which I doubt is the meaning. Recovering signals below the noise is certainly possible, but that is not my real concern. It does however seems as though the author is comparing a thermal noise in Watts to something that is not well defined. I am guessing that the -130 dBm is the power collected by a dipole or isotropic radiator, but whatever it is, the units in the text make no sense to me. Dave _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
