Re: SETI ET's problem with Doppler.


Yvan Dutil (Yvan.Dutil@drev.dnd.ca)
Thu, 09 Sep 1999 11:57:14 -0400


At 04:24 PM 9/9/99 +0100, prewar wrote:
>After all, if ET is trying to let us know he is there, then
>from his point of view it would be worth some effort on
>his part to ensure that all Doppler effects everywhere, are
>completely negated. He will be aware that the listener's
>problem is greater than his, in not sweeping his own TX freq.
>
>So, are we all wasting valuable PC time in listening at all
>those many 10Hz bins etc. so advocated? Would a much
>more sensitive search be done by just listening to 1420 MHz,
>and wait until ET's TX signal 'sweeps' by?
>
>In fact, perhaps we only need to monitor somewhere near
>to 1420 MHz, and await the Doppler effect on ET's varying
>freq. signal to sweep him right into our waiting laps!
>
>As most/all of you are 'bin' searchers, I guess my argument
>is flawed somewhere.....but I'm surely tempted to stay right
>by the 'waterhole, and dream of Doppler!. :-)

Yes, thgis argument is flawed. There not much gain to have a
frequency stabilised on the reciver end. First, I dont see
how it can be done, since we need to know everything about
the receiver including the coordinate of the receiver on the
planet! Second, the Dopler drift allow you to differanciate a
guinuine ET signal for a local transmitter. Third, actual
SETI system survey large chuck of the radio spectrum at one with
a fairly high duty cycle. Restriction on communicationnal capability
and the information to be transmitted, lead to a minimal duration
for a message of a signifiant fraction of hour.

By the way, there is no reason why 1420 MHz shoudl be the optimal
frequency. Antthing betwenn 1 and 10 GHz could do the job.

Yvan Dutil
 



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