"Rob Dekker" skrev
news:U3itc.57621$U4.32640@newssvr29.news.prodigy.com
Hi Mogens,
Your enthusiasm is intoxicating, but I think you misunderstood David's
reply
especially regarding some of the technical aspects of unphased small-dish
receivers.
Yes, indeed :-(
The Hz within 1.42 GHz refers to the bandwidth in which you are receiving.
Read SETI FAQ.
I understand bandwidth (thank You).
(+/- x Hz.)
fx. 1,42 GHz +/- 5000 Hz.
Correct ?
Every Hz of bandwidth contains kT (Bolzmann constant times system
temperature) Watt of noise power. ...
By this You mean, that noise from 1,42 GHz -5000 Hz to +5000 Hz is greather
that, noise from just -50 Hz to +50 Hz ...
Correct ?
... And therefore at signal will drown in noise, then we are useing a big
bandwidth.
Correct ?
... So to reduce noise SETI@home scans many,
many very narrow bandwidth portions of the spectrum around 1.42 GHz. ...
By this scanning You mean, that the SETI-computer-program is in able to
separate one frequence from another, and by this reduce the noise on this
frequence ?
... The
general assumption amount SETI activities is that interstellar radio
beacons will transmit in very narrow bandwidth exactly ...
But the the signal is more difficult to find :-(
... because wide band
transmissions are easily lost in the noise. ...
Yes ...
... Light-year distances, and the
inverse-square law does horrible things with even the strongest signals.
:-(
To detect any signal in microwave range over such distances,
you need big antenna's (Arecibo-size),
I have �ne objection on this point:
Are we looking for someone like us ?
NO! - We just want contact.
An "old" civilization with millions of years in space will send out really
BIG "Hello"-signals, because they know, how difficult it is to find them.
If Arecibo can do over 1E13 Watts in output, perhaps they can do more than
1E17 W.
Is this technical possible ?
(fx. more than 1000 parapol's mixed together)
Can we "download" such kind of big signals by a little 2-4m parabol ?
and sender and receiver antenna have to point at each other,
Yes, of course - that's our problem :-(
and the sender needs to transmit with TerraWatt (EIRP) power levels,
TerraWatt ?
Do You mean by this 1E12 W?
and they have to be tuned to the same frequency,
Yes, of course - that's our problem :-(
and they should have matching bandwidth.
:-|
If one of these things is not there (for example, small receiver antenna,
or listening to wide bandwidth), then the signal is not detected at all.
Yes, of course.
So, if there are thousands of small dishes which are all pointing at
different parts of the sky (as you suggest), and there is one ET signal
out there, then only one small dish points at the transmitted signal. ...
Correct! - *�ne* will get the right position, at the right time, and at the
right frequency :-)
(look above, 1E17 W as output)
... And since
it is a small dish, there is a good chance that the signal disappears in
the noise, ...
Also when the output is more than 1E17W ?
... so we still don't detect anything. ...
Und das ist nich so gut :-(
... You need 1 million big dishes to
detect that signal (larger dishes have a narrow beam, so you need more to
cover the sky).
Arecibo 1E13W * 1E6 (as output) = 1E19W
But ... if they send out the signal with 1E19W, what then ?
Is this technical possible ?
(fx. more than 100.000 parapol's mixed together)
Or, you need ONE big phased antenna (which can listen to as many
different
directions (beams) simultaneously as its phase-processing computers can
handle).
But then You also get's the noise from all these directions!
... The Allen radio telescope for example. So that is a revolutionary
new development.
Do You have a web-side ?
Maybe now you see that even though microwave organized SETI has been done
for a decade or so, we still barely scratch the surface. There is so much
to explore still.
Yes,
To get back to your plan, Arecibo is only listening to one spot in the sky
at one time, and thus it might miss some really loud signal from somewhere
else. ...
Correct :-(
... So, an immensely strong and short (maybe switched on for a few seconds
only once/week or so) is easily missed by even all the seti searches so
far.
Correct :-(
If that is true, then your idea (of many small amateur dishes around the
world) might actually detect that signal.... You never know.
Too bad :-(
Rob
P.S. We really have no idea what kind of information any ETI would send
out.
May I come with a suggest ?
Are you in able to crack the code, se ...
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(You can win around 140 US $, if You are the first one)
If it's some sequence of numbers or so, pulse-spaced, whatever, we dont
know. We should not anticipate.
But we DO know that is we find a signal (continuous or slowly pulsed) with
bandwidth smaller than 100Hz or so, then it comes from a artificial source
(ETI), since mother nature does not produce such signals. So narrowband is
good for two reasons (less noise, and receiver knows that it is ETI-made).
Did You understood my point in regard to this:
1.
Time = 0 ............ (1. impulse)
Time = 1 ............ (2. impulse)
Time = Phi (22/7) (3. impulse)
The final proof :-)
Thank You for Your answer, Rob.
With kind regards,
Mogens Kall
The servant of Michael
Win (vind) 1000 Danish Kr. (around 140 US $), jump ...
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