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"spontaneous" LEILA activation

I frequently hear unexplainable LEILA sirens in the vicinity of 2401.400 MHz
where there is hardly ever any transponder activity.  Once this weekend I
was tuning across the transponder and heard the LEILA siren go nonstop for
more than 90 seconds.  I don't know how long the siren was going before I
stumbled onto it.  When I hear "spontaneous" LEILA sirens I verify that my
uplink signal is notched, just to ensure that nobody is uplinking a
recording of the LEILA siren.

Could there be a powerful U or L-band terrestrial interference source that
transmits brief pulses or high-speed data that is not audible on the AO40
downlink?  What other theories could explain why LEILA seems to activate for
no apparent reason?

Wayne Estes W9AE
Mundelein, IL, USA

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