| |
VK2ZRG > SETI 04.12.04 15:49l 60 Lines 3023 Bytes #999 (0) @ WW
BID : 975_VK2ZRG
Read: GUEST
Subj: SETI...WB6YRU and KB2VXA
Path: DB0FHN<DB0MRW<DB0RGB<DB0AAB<F6KFT<LX0PAC<ON0LGE<DB0LJ<DB0RES<ON0AR<
7M3TJZ<IW8PGT<CX2SA<W4JAX<N2BQF<VK6HGR<VK5UJ<VK5BRC<VK5ATB<VK2AAB<
VK2WI
Sent: 041204/0845Z @:VK2WI.#SYD.NSW.AUS.OC #:55664 [SYDNEY] FBB7 $:975_VK2ZRG
From: VK2ZRG@VK2WI.#SYD.NSW.AUS.OC
To : SETI@WW
VK2ZRG/TPK 1.83d Msg #:975 Date:04-12-04 Time:8:08Z
Hello Gary, Warren and readers,
To Gary first, I was commenting on what I
heard on the wireless, so it could be said to be a `media' version of the
real facts. I would hope that the SETI people have done the sums, and know
that 'eavesdropping on ET' is a waste of time. You are, of course, right
when you say "We'll never know unless we look"; but what if everyone is
listening? I have a vague recollection that some transmissions were made
from Arecibo many years ago, but were discontinued because it was thought
prudent not to advertise our existence on Earth.
I'm not quite sure what you mean by "next generation of receivers".
In terms of sensitivity or system noise temperature, they are NOT going to
get very much better than they now are. There are already liquid helium
cooled LNA's with noise temperatures under 10 Kelvins and commercially made
10 metre dish antennas rated at 10 Kelvin noise temperature for C band. I'm
not sure what the Arecibo antenna noise temperature is, but there would be
a fair amount of `ground noise' leaking through the mesh at 1 GHz.
I know a fair amount about this subject, having worked in the Department
of Astrophysics at the University of Sydney, for 10 years before my
retirement. During that time we totally replaced all the receiving equipment
and local oscillator system for the Molonglo Observatory Synthesis Telescope,
or MOST. This telescope, by the way, has many times the collecting area than
the famous "Parkes Dish". The Molonglo antenna is an East-West paraboloid, 12
metres wide by 1600 metres long. In the ancient measurements, that's 1 MILE
long. The antenna is steered mechanically North-South, and electrically
East-West.
Antenna requirements for radio astronomy and SETI are not quite the same.
For radio astronomy, the requirement is a large base line to increase the
resolution. For SETI, the name of the game is square metres of collecting
area.
Now to Warren. I'm sure a time of ten seconds per frequency was mentioned
in the item that I heard on the wireless. That might be long enough if ET
was using megawatts of real power into a antenna the size of Arecibo or
larger, AND, had it beamed exactly in our direction.
As for the `eavesdropping' idea, forget it!
I do know of the Moon bounce activities of amateurs at Arecibo, Warren, and
I guessed that Arecibo was used for the planetary radio mapping programmes.
but I wanted to keep it simple.
I don't think that even with 1500 watts, an `Amateur' transmission from
Arecibo would get anywhere near a Terawatt. Tera is the prefix for 10 to
power 12 (10^12), so with 1500 watts or +32dBw, and 60 dB antenna gain,
you only have 1.5 Gigawatts or +92dBw, a touch short of a terawatt. The 3TW
signal would have to be a 3MW input, pulsed radar signal, into the Arecibo
antenna.
Merry Cricket, HO HO HO
73s from Ralph VK2ZRG@VK2WI.#SYD.NSW.AUS.OC
/ack
Read previous mail | Read next mail
| |
