In message <4caba343.8c581...@cox.net>, WB6BNQ writes: >Please explain to me how spread spectrum would enhance any process > of frequency or time recovery ?
Ok, it is late and I'm probably going to botch this, but I'll try: The really short explanation is that your carrier transitions have random-ish looking signs, which, if properly designed, allows you to balance out pretty much any kind of CW or random noise. This is, in essence, why you can separate the different GPS sattelites, even though they all send on the same frequency. Technically speaking, Loran-C is spread spectrum, but they botched this aspect slightly, by not properly balancing the signs of (all) the codes. The Austron 2000 has a switch that allows you to disregard certain bits in the codes to balance them, this increases the imunity to CW interference. So given that you can trivially get a good OCXO today, I would design our "low-power-time-transmitter" to send one fix per hour. For instance 127 bits of PRNG at 28 seconds per bit with a four second gap before the next timestamp (send ID ?) On the receiver side, you know what time it is +/- one 28sec bit, so you digitize the signal and correlate the PRNG in a window around your local clock. After an hour, you pick the correlation bucket that correlated best and have an instant estimate of the difference between your local clock and the average of that hours transmissions. If xmitted as NFSK at around 100kHz and digitized at 1MSPS, you would get 1µsec resolution without resorting to interpolation. By choosing all your magic numbers to be nonprime to normal CW signals inside their respective periods, you supress those by averaging. This is why the NELS LORAN-C chains got new 4-digit GRI's: they are imune to pretty much traditional CW interference because they do not divide seconds or kHz on relevant timescales. Poul-Henning PS: DCF77 already does SS, but on a second to second basis. -- 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.
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