SETI ET's problem with Doppler.


prewar (prewar@btinternet.com)
Thu, 09 Sep 1999 16:24:00 +0100


Hello,
If the following argument has already been covered
I'm sorry, but only been on these two newsgroups for a few
months, but haven't yet seen it aired. It may have been covered
on the closed Project Argus group, but I'm not on that.

At 1/2 mile per hour the Doppler effect will shift the
Hydrogen line freq. approx. 1Hz.
The earth's speed around our Sun is roughly 18 miles per
second and will shift Hydrogen line approx +- 150KHz.
(This, of course, will only happen if one's antenna is looking
along the direction of the Earth's travel, and not 90 deg. to it.)

As ET will most certainly be aware of all this from his own
Planet/Sun system, he will realise that transmitting on
1420 MHz Hydrogen line, will never reach any one else
at anything like this freq., unless we are all extremely lucky
and his own TX beams out at 90 degrees from his orbit around
his Sun and we are in-line and receive him in a similar configuration,
so that the Doppler effect is minimalised. Also if we are
very, very lucky and that he is not travelling toward/away
from us within our own galaxy or beyond etc. How lucky do we
have to be ?........!!!

Because of this I would take a fair guess that ET will
sweep frequency +- some few MHz either side of the
Hydrogen line, in order to be certain that anyone,
anywhere, no matter what their relative speed to him,
will always receive a signal on 1420 MHz. at some point
in their listening. If you wish to contact someone then
you would go to some slight extra trouble to greatly increase
your chance of success, would't you?

ET will not continually sweep, but step his TX freq.in
small steps over a time period which he considers to
be long enough for us/others to lock onto.
The problem here is that his time scale may differ
from ours......he may only live a few hours lifespan
or 1000 of years in our own terms, so what he considers
a suitable time frame may be too fast/slow for us!

But an intelligent being would be aware of this and take
this into account, by vary the speed of sweeping his
TX, on a regular repeating basis.

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!. :-)

Regards

albErT !!



This archive was generated by hypermail 2.0b3 on Sun Oct 10 1999 - 15:46:34 PDT