archive: Re: SETI modulation of ETI transmission

Re: SETI modulation of ETI transmission

Richard Burke-Ward ( richard@burke-ward.demon.co.uk )
Wed, 2 Sep 98 16:54:00 +0100

Daniel Boyd wrote:

>Now, one discovery in research on fractals were sounds that when recorded
>and played back at half speed sounded the same. In fact, there were a lot
>of interesting tricks that could be played with these fractal sounds. If
>these tricks can be done with sound then they can be done with radio
>waves. Doppler shifted white noise still sounds the same, but there may
>well be another nonsinusoidal radio wave that will stand out in the noise
>and not be effected by doppler shift.

First I should warn you that I know next to nothing about about radio or
about fractals. But it seems to me from first principles that:

Daniel's idea ought to be possible for a carrier wave - presumably you
would notice a small amount of doppler shift depending on the relative
speed of transmitter and receiver, but at a slightly higher or lower
relative speed the signal would appear to drift back into 'tune' as the
next level of fractal structure (up or down) emerged. But making the
signal carry *data* would be trickier, because data is esssentially
conveyed by alterations to the basic carrier structure - substract the
carrier and you're left with the content... So the data would also have
to be reproduced independently on every fractal scale - and therefore
contained within one 'repeat cycle' of the fractal shape. Presumably
(and I'm no mathematician) this would then limit the fractal dimension of
the amplitude curve - because if each fractal level was too close in
scale to the one above and below, the data content would start to
'interfere' with the same data being carried at the scales immediately
above and below.

So to compensate smoothly for doppler, you need each fractal level close
to each other level - but in the process you reduce your data capacity
until you're left with nothing but a carrier wave and no signal content...

Richard