Re: [Discuss-gnuradio] Car alarms and garage door openers

[Marcus Leech]

Matt Ettus wrote:
> Thanks for looking into this.  I think that most keyfobs use SAW 
> oscillators instead of crystals to save money.  This results in very 
> bad frequency drift, which the receiver will need to compensate for.
>
> Matt
Many of these systems use OOK (On/Off Keying) of the SAW-based 
transmitter.  The receiver is a wideband
 TRF design, with square-law detector and post-detector gain.   The 
fact that the transmitter drifts is of little
 consequence, since the receiver has a large bandwidth.  Since each 
receiver has a "unique" address code
 that it responds to, the fact that there may be other transmitters in 
the vicinity doesn't seem to matter that
 much.