[time-nuts] 60 KHz Receiver

[shalimr9 at gmail.com]

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" <phk at phk.freebsd.dk>
Sender: time-nuts-bounces at febo.com
Date: Tue, 05 Oct 2010 10:44:39 
To: Discussion of precise time and frequency measurement<time-nuts at febo.com>
Reply-To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] 60 KHz Receiver

In message <B69FDCAF-2B39-4575-B5CD-66A87FA1B332 at 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
phk at 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.

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