Mike Keitz wrote:

> Go with AM in the 312 MHz garage-door opener band.  The transmitter is
> just a single transistor oscillator with a printed coil operating as both
> the inductor and the antenna.  The receiver is a regenerative design with
> a single transistor doing all the RF, typically followed by an op-amp for
> baseband gain.

  You mean a Super-regenerative (Superregen) receiver.  These things
play
havoc with my UHF CB (467 MHz) when you pass or park near a car with one
of
these burglar alarms!  Very suspicious!

> However, because the receiver is an oscillator, it will likely interfere
> with other nearby receivers (garage door opener receivers often use an RF
> amp to improve sensitivity a bit and also reduce the regen oscillator
> leakage back out the antenna.

  The best ones use an RF Monolithics (or equiv.) SAW filter between RF
stage
and superregen, as well as a SAW resonator locking the transmitter
frequency.

  Cheers,
        Paul B.