Re: garage remote jamming

["Jeff Volp" <JeffVolp@xxxxxxx>]

"Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote in message
news:WoSdnfla97CuGXXYnZ2dnUVZ_tLinZ2d@xxxxxxxxxx
> "Jeff Volp" <JeffVolp@xxxxxxx> wrote in message
>
>> There is a technique that uses spread-spectrum and correlation between a
>> received signal and a pseudo-random pattern.
>
> Sounds interesting.  But as Dave notes, when you are talking about
> spread-spectrum techniques, you've strayed outside the limits of my
> original
> words "same frequency."
>
> I am sure that by using multiple frequencies and high levels of redundancy
> that a delayed radio message can be sent intact through heavy
> interference.
> It will always take longer than a straight-up message sent on a single
> frequency because of the reconstitution required.

Spread-spectrum not as complex as you may think.  It does not involve
multiple transmitters running on different frequencies.  The pseudo-random
digital pattern is used to modulate a single transmitter, causing its output
to look a lot like noise.  The receiver has a copy of the pseudo-random
pattern, and uses that as an input to the correlator.  When the patterns
exactly line up, the correlator produces a valid output.  All you get is
noise if just one bit off.  As I recall, the P-code bit rate is 10.23MHz, so
each bit is only 98nS.  Data is modulo-2 added to the pseudo-random code,
and the result modulates the transmitter.  So, when the codes are aligned at
the receiver, the data pattern comes out the correlator.

Jeff