Ok, so this is going to sound really weird, but please bear with me.
For the last several evenings, at exactly the same time, my radio
astronomy receiver has been receiving a series of square waves,
of amplitude about 100Jy (large by radio astronomy standards, tiny by
anybody else’ measure of such things). These are
near-perfect 50% duty-cycle square waves of period approximately 166
seconds, with an initial lead-in of a few minutes,
then a series of, ahem, 1s and 0s, then trailing off to nothing.
While it’s far-fetched that someone would put an easter-egg in that
would only be obvious to my application, it’s not
inconceivable. So?
Obviously, there are lots of other explanations, like a strange radar
that I haven’t seen before, some kind of bad-ass
ionospheric sounder that makes my local ionosphere slightly opaque to
21cm radiation in a square-wave
pattern. Or one of a number of other types of weird RFI sources. I
found nothing in the spectral display,
so whatever it is seems to be either broadband in nature, or
narrowband, and driving my LNA into
slight compression in a square-wave like pattern, but outside of my
receiver passband.