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

From: Marcus Leech
Subject: Re: [Discuss-gnuradio] Car alarms and garage door openers
Date: Tue, 06 Jun 2006 14:42:02 -0400
User-agent: Thunderbird (X11/20060516)

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.


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

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