[ExI] We just got harder to find

[Jordan Hazen]

On Sat, Jun 13, 2009 at 11:29:29AM -0400, John K Clark wrote:
> If ET exists it will be harder for him to detect a civilization on Earth 
> now than it was 24 hours ago. The reason is that today every analog TV 
> station in the USA will be permanently shut off; the digital transmitter 
> replacements are far less powerful.

I've had similar thoughts.

DTV modulation schemes, both American 8VSB and Europe's COFDM, look
far more random and noise-like on a spectrum plot, so even without the
drop in power, they'd be less likely to stand out from natural
background sources.  Both standards include a deliberate "scrambling"
process (not encryption) that seeks to spread RF energy evenly across
the channel, also mixing up the packet sequence, both measures helping
to resist interference and improve effective signal/noise at the
receiver.

Someone who did manage to pick one of these out from background hash
would have a huge reverse-engineering job on their hands to decode it,
with so many nested layers of arbitrary, non-obvious structure, from
RF level all the way up to MPEG2 video and Dolby Digital sound.

NTSC and PAL, by contrast not only have quite distinctive energy peaks
at the visual and sound carriers to attract attention, but the
encoding, sync pulses, line structure etc. are so simple that any
technically competent entity shouldn't have much trouble quickly
figuring them out.. at least for black & white video + sound.  Color,
if its subcarrier is noticed at all, might take a few days more.

> John K Clark

-- 
Jordan.