That is basically the sauce behind GPS. What is the power of the transmitters on the satellites? It can't be much, and the signal on the ground is quite a bit below the noise floor before correlation.
Didier Sent from my Verizon Wireless BlackBerry -----Original Message----- From: "Poul-Henning Kamp" <p...@phk.freebsd.dk> Sender: time-nuts-boun...@febo.com Date: Tue, 05 Oct 2010 10:44:39 To: Discussion of precise time and frequency measurement<time-nuts@febo.com> Reply-To: Discussion of precise time and frequency measurement <time-nuts@febo.com> Subject: Re: [time-nuts] 60 KHz Receiver In message <b69fdcaf-2b39-4575-b5cd-66a87fa1b...@rtty.us>, Bob Camp writes: >Even though it's pule, the RF power is way beyond the sub 1 W >outputs currently contemplated on those bands. Signal to noise >*does* matter. You know, there are other ways to skin that cat these days. Old-time signals had to be grossly inefficient because the receivers were inefficient, in particular the "ear-wristwatch" kind of time receivers. These days we have spread-spectrum modulation, and if our only goal is to transmit a timestamp, you can spread pretty wide and far and need very little power to produce a receiveable signal at long distances. The QRSS hams are playing around with numbers like 17,840,000 miles per watt, and all it takes to turn that into a time/frequency services is a spreading function with a really good autocorrelation. Obviously, you will not get second by second measurements, but the measurements you do get, say once per hour, will have much higher precision because of the averaging that goes into them. And equally obvious: propagation effects will take their toll, but still... Somebody with a license should try that on 137kHz... Poul-Henning -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ 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.