Re: garage remote jamming

["Jeff Volp" <JeffVolp@xxxxxxx>]

"Dave Houston" <nobody@xxxxxxxxxxxx> wrote in message
news:45e9594b.914007187@xxxxxxxxxxxxxxxx
>
> I believe Jeff was describing DSSS (Direct Sequence Spread Spectrum)
> which does use only one carrier frequency but is still subject to
> jamming. See...
>
>     http://rfdesign.com/images/archive/0900McCune90.pdf
>

That looks like an excellent reference document.

Yes, GPS uses DSSS.  While not immune to jamming, it does tolerate moderate
power narrow-band signals within its bandpass.  Its resistance to jamming is
a function of the data rate.  From the summary:

"If there are narrowband interferers of moderate level, then a DSSS system
that will completely reject them may be designable.  Should there be large
interfering signals, then a DSSS link may completely fail while FSSS is
likely to continue operating even though the interference is not complete
rejected."



The difference is that a jammer may totally block of the discrete
frequencies in the frequency hopping link, so that information is lost.  The
integrator in the DSSS link can reject the jammer until its energy dominates
the summation.



Jeff