[time-nuts] PN sequence generation using GPS

[ehydra]

Spread-spectrum and similar schmes were a little kind of secret and 
secure communication around 1970 where the mathematics where done in the 
years before, beginning with the classic Shannon paper about information 
theory. Many papers were classified to help protect the knowledge their.

Especially for the military it was interesting because the average 
knowledge level was low for this and the machinery to crack the code on 
air was way more expensive the average bad 'terroris't would effort.

As it became common to have FFT-based receiver equipment 'for cheap' 
this doctrine wen't useless. Useless the same as thinking atomic bombs 
will secure freedom.

If one looks in the spectrum in a very fine granular structure the data 
transferred by SS will be seen on every single spread-code bit!! All 
needed is a high-enough S/N and a lot of computing power. On the analog 
side the receiver must be very strong signal capable so other 
'intruders' will not be mixed-in in the wanted signal.

A FFT ist nothing more than an integration on every small frequency step.


- Henry


scmcgrath at gmail.com schrieb:
> Hi Chuck,
> 
> Serious contesters have directional antennas and most of the new contest quality rigs have FFT spectrum displays and the ability to record several Mhz of spectrum directly to disk for later analysis.   
> 
>    The old stereotype of unsophsticated home brewed gear is now a subculture of the Ham community.
> 
> These are the guys who will hear you and FIND you esp since most of these guys have north of 50k invested in their stations and anything which interferes with getting that last elusive multiplier will be tracked to the end of the earth. 
> 
>  and some of them like me are also time-nuts.
> 
> 
> Sent from my Verizon Wireless BlackBerry
> 
> -----Original Message-----
> From: Chuck Harris <cfharris at erols.com>
> Sender: time-nuts-bounces at febo.com
> Date: Fri, 25 Feb 2011 13:16:13 
> 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] PN sequence generation using GPS
> 
> I guess that is why I mentioned something about doing it competently.
> 
> The FCC so seriously winged the methods usable by hams as to render them
> effectively useless.
> 
> A nice direct sequence spread spectrum system with a couple of MHz
> spread would be well below the background noise of any narrow band
> receiver.  Sure, you could find it with a wide band detector if you were
> close by, but how would you know that you weren't looking at some other
> anomaly, like a bad insulator, or trash coming off of fluorescent lamps?
> 
> Done correctly, you could run spread spectrum just about anywhere you wanted
> to, and remain undetected.  Using direct sequence, you would be so low in
> power density that it could easily be argued that you were operating within
> the constraints of a part 15 device's leakage.
> 



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