archiv~1: Re: SETI Multipath

Re: SETI Multipath
Sat, 21 Nov 1998 08:44:53 EST

In a message dated 11/21/98 7:52:44 AM Eastern Standard Time, writes:

I think what he is talking about is called frequency diversity in
short wave terrestial radio systems; you transmit on several frequencies
and then select the strongest one as the one to output in the receiver.
Although its not quite the same thing as short term fading, short wave
broadcast stations transmit on many bands simultaneously to ensure that
at least one will get through to its audience (which is not to say that
you couldn't design a frequency diversity system, only that it would
be overengineering for domestic use).

The other approach in terrestial systems is spatial diversity, where
you have multiple receive antennas, on the basis that when the
multipath signals cancel at one antenna they will add at another.
I suspect the very narrow angular spread of the signal means that you
would need impossibly large spatial separations to use this in a
SETI context.

The trivial method is time diversity; repeating the same transmission
over and over.>>

Nice job!

Yes; it is a FHSS mode which uses frequency diversity for the highest
probability of intercept:-)! The nice thing (also) is that the ratio of freq's
is invariant so you can use this as a noise rejection method toi get diversity
gain:-). Hence 'Doppler invariant pattern recognition' or dippr')

Chip N1IR