archiv~1: Re: SETI Arecibo message to m13

Re: SETI Arecibo message to m13

David Woolley ( david@djwhome.demon.co.uk )
Wed, 11 Nov 1998 08:10:08 +0000 (GMT)

>
> Perhaps. Myself, I'd go with the FFT time span and avoid averaging
> altogether. Well, I'd overlap the FFT's maybe 50% at most.

The reason that one averages is that you need a lot less stability in the
signal and system. Sources of instability, outside of the receiver include
unknown doppler chirp and multi-path propagation effects (the latter are
generally quoted as spreading the signal by about 0.1Hz). As far as I
can tell you get better signal to noise ratios by using the time for
more FFT points, but only if the signal is ideal enough.