Newsgroup: it.scienza.astronomia.seti
Titolo: antenna

Astronomic antenna
This article describes an idea for an antenna aimed for communication over a
very large distance of astronomic units and beyond the solar system.
The method of the antenna is in contrast with the attitude today, and I ask
the reader to be positive as much as possible with it.
Description of the antennas used today
The antennas used today are of this type:
 Large dish antennas, having a diameter of about 30 meters that work at the
microwave range. These antennas have a reception area of about 1000 square
meters. These antennas must be aimed to the transmitting source at a very
high accuracy of 1 million.
Large radio frequency antenna fields, (like HAARP) having an area of 100,000
square meters. These antennas can transmit frequency in the range of 2-10
MHz.
Large radio telescope (ARECIBO), having an area of about 100,000 square
meters, working at a frequency of 300-9000 MHz. This antenna must be aimed
exactly at the transmitting source to receive its signal.
4000 microwave dish antennas of 5 meters in diameter and a total reception
area of 100,000 square meters. These antennas must be aimed exactly at the
source to receive the signal.
We can see that these antennas have two main parameters:
The area they receive is 100,000 square meters.
They must be aimed at a very high accuracy of 1:10,000,000 over the sky
sphere, to receive the signal.
Microwave antennas are very directional
Microwave antennas are too directional. The antenna receives only from a
tiny part of the sky. The method is like directing a laser beam, and
detecting it with a very short angle telescope.
Microwave antennas are very frequency selective
In addition to this there is the question the selective frequency: Microwave
antennas work at a very selective frequency. The antenna has its good
amplification thanks to selecting the exact wavelength. There is no wideband
microwave antenna that receives over for example 2-12 GHz. If such an
antenna will be built, it will lose its advantage of low noise.
The pathfinder spaceship to mars used for example a carrier wavelength of 8
GHz, and a bandwidth of only 80 KHz. The ratio being 1:100,000. In other
there are 10,000 channels between 8-9 GHz.
There is not even a special reason that the signal from another civilization
will use a 80KHz bandwidth like we will try to detect on earth. Even if they
will accidentally use such bandwidth, still the chance that it will fit
exactly to the channel received on earth is 1:100,000.
This lowers the chance to detect life by 100,000 times.
Since each antenna has a gain and directivity of 10 million, the chance to
make accidental communication is e-14.
Since the bit-rate in that kind of communication is very slow, less than 1
bit per second, even if we scan the sky for years, it will be impossible to
detect anyone.
And in numbers: If the bit-rate is 1, and we need 10 bits to detect
intelligent signal. Than we need to stay 10 seconds on each scanning point.
It will take us 80,000 million years to scan all the sky using that method
and to make accidental communication.
We see that the high gain and directional antenna is not an advantage for
that purpose.
Microwave antennas receives a small signal
A 30 meter dish antenna has an effective area of about 1000 square meters
only. The parameter "gain" relates to how much electrical current the
antenna generates from the electromagnetic signal. As gain of 1 relates to
one dipole having a length of 1/2 wavelength. In the case microwave gain of
1 means very little electricity because such a dipole is very tiny antenna
having an area of 1 square centimeter.
The gain of 70 db is 10,000,000. For a 1000 square meter area dish antenna
it means that it has the capacity to generate electricity like 10,000,000
million antennas, each having an effective area of 1 square centimeter.
The capacity of that dish antenna of generating electricity is not more than
of a simple 30 meter dipole antenna. Both antennas will have the same
efficiency of generating electricity from the same electromagnetic wave.
It is like to compare the work of 10 million ants with the work of one
elephant.
If we need to transfer megabytes per second, than we must use high carrier
frequency, but the fact is that when the signal is weak we must lower the
bit-rate in order to detect it.
The communication with Mars today is at 5Kbits per second. For that bit-rate
we can actually use frequency of 5 KHz and we don't need to use 10 GHz.
Antenna amplifier noise
A 10 GHz antenna amplifier does not have less noise than a 5 KHz antenna
amplifier.
A simple, low cost, not cryogenic, low noise, low frequency amplifier will
have an input noise of e-23 watt (1. (
The noise of a cryogenic cooled microwave antenna is about the same, being
e-21 watt (2). As the frequency of the input amplifier is lower, there is
less noise from it.
Since the internal amplifier noise is the same, than the signal amplitude
becomes the major important factor. Large area antenna will have large
signal.
Long antenna can be directional and have higher gain
Using a reflector and an element will allow increasing the ratio by 10 or
more, if it is needed.
A long dipole antenna is much more sensitive than antenna arrays on Earth
If we put a 50KHZ dipole antenna as a satellite to Earth, it will be 3
Kilometer long. The wavelength will be 6 kilometers. The effective area will
be 3000 ^2 square meters. This is 9 million square meters. This is about 100
times more than the HAARP array, the radio-telescope or the 4000 dish
antennas of 5 meter.
The ratio between the received signal power and the transmitted signal power
depends only on the effective area of the antenna and the distance (3). The
ratio is:
The wavelength ^ 2
------------------------
The distance ^ 2
In the case of a signal transmitted from 200 million Kilometers, using a 6
Kilometer wavelength, the ratio will be:
6 ^ 2 / 200 e6 ^2 = e-15.
A 10 watt transmitted signal will be received at e-14 watt.
This received power is 1000 times stronger than the signal that we receive
today from Mars, using sophisticated high gain microwave antennas.
A dipole antenna more far from Earth
If we put the antenna more far from Earth, the temperature of it will be
lower. At lower temperature the electrical resistance is lower. If the
antenna will be at about 3 AU from the Sun, we can multiply its length
without multiplying its weight. The active area and the sensitivity will be
increased by 4. The frequency will increase by 2.
A dipole antenna made of a superconductor
If we are more advanced, than we can make a superconductor cable and send it
to a place were it is cold enough to be superconductive.
The superconductor dipole will be 30 Kilometer long and will work at 5 KHz.
The antenna will be positioned at a distance of about 6 astronomic units
from the Sun.
The 30 Kilometer antenna will weight less than 100 Kilograms because
superconductors have 200 times less electrical resistance than copper. At 6
AU it will not need a coolant since superconductors today work at 77 degrees
Kelvin. There are already low cost flexible superconductors used by the
power stations (5))
The effective area of a 30 kilometer long dipole antenna is equal to 10,000
HAARP arrays.
At that frequency and distance from the Sun, the noise level of the antenna
will be very low. The noise will be much less than the noise of microwave
noise coming from Sun or other stars.
The most powerful signal at frequency of about 5 KHz are generated at 150 AU
from the Sun,  these waves are also confined to lower frequencies and they
are not a problem at 5 KHz beyond 10 AU.
Frequency of 5 KHz cannot reach the Earth because of the electron ion plasma
around the Sun that blocks all frequencies below 20 KHz from reaching the
Earth.
The same physical laws here will also work for any other civilization or a
place like Earth.
In order to receive and transmit at large effective, they also need large
antennas and low frequency.
There is much less low frequency noise in space, than high frequency noise
or microwave noise. The source of the noise is the Suns. The ion plasma
around the Suns blocks the low frequency much more than it blocks high
frequency.
In our Sun the cutoff frequency is 20 KHz at 1 AU from the Sun, 10 KHz at 2
AU and 5Khz at 4 AU. Frequency 1 MHz frequency is blocked at 0.01 AU from
the Sun.
One photon detection
Low frequency electromagnetic waves, like optical waves, are made of
photons.
Like it is not possible to detect a light signal, having energy less than
one photon, it would not be possible to detect a radio signal, having energy
of less than a photon.
The closest star to us is 240,000 Astronomic units from us, or
36,000,000,000 million kilometers.
If a signal from other civilizations will enter the solar system, and
received by an antenna, it might be not more energetic than few photons.
There is a ratio between the powers of the photon and the wavelength.  A
photon at a frequency of 10 Gigahertz is million times more energetic than a
photon of a frequency of a 10 KHz.
Because of this, the weakest signal that can be detected at 10 KHz is
1,000,000 times less powerful than the weakest signal that can be detected
at 10 GHz.
Background Noise
The background noise above 1 AU from the Sun is less than instrumental
noise, and below e-16 (4).
The frequency and the intensity of the plasma oscillation show a tendency to
decrease with increasing radial distance from the Sun.
Solar radio bursts tend to be more intense at higher frequencies, which are
generated closer to the Sun, and not by lower frequency, far from the Sun.
First contact communication
When Galileo spaceship wanted to communicate with Earth, it first
transmitted using a simple dipole antenna, using low frequency.
Only after the first communication was done, and the position of Galileo was
known on Earth and Galileo knew where Earth is, only then a microwave
directional communication have started.
The microwave transmitter and receiver on Earth had a matched frequency and
bandwidth. Without this they would not communicate.
The chance to start a communication with directional dish antennas, with
another civilization is zero.
The chance to start communication a non-directional, long dipole antenna in
space, is at least e12 higher.
If we want to detect other advanced civilizations, we should give this idea
a chance and support it.
It is a fact that we spend billions of dollars over decades trying to
communicate with other civilizations, using microwave methods, and we
failed.
By Gil Teva ( 
gil...@actcom.net.il
 )
(1) 
http://www.femto.de/datasheet/DLPVA100BUNS.pdf
(2) 
http://www.ka9q.net/mpf_budget.html
(3) 
http://farside.ph.utexas.edu/teaching/jk1/lectures/node83.html
 (formula 1001)
(4) 
http://www-pw.physics.uiowa.edu/plasma-wave/helios/summary/summary.html
(5) 
http://www.amsuper.com/html/newsEvents/news/105793757741.html
Telefax: 02-6724273
Email: 
gil...@actcom.net.il

Antenna for detecting other civilization
It is a fact that for many years billions of dollars have been spent to try
to locate other civilizations, but without a success.
The method used was using high frequency radio waves using large antenna
dish antennas.
These antennas can communicate with very far spaceships, even at a distance
of 100 AU. But they are not suitable to make contact with other
civilizations because of 2 main reasons:
1.      The antenna is very much directional and receives or transmits
signal only to a very narrow angle in the sky. A 70 db antenna ha an angle
of only 1 part of 10 million of the sky. To detect signal from other
civilization using such antenna would not only require that the antenna will
be aimed exactly at the transmitting antenna of that civilization, but also
that the antenna of that civilization will be aimed exactly at Earth. The
chance that this will occur is 100 e12.
2.      A large dish antenna used today transmits in a narrow bandwidth of
64 KHz using a carrier frequency of 8 GHz. The ratio between the two
frequencies is about 1:100,000. If an antenna from another civilization will
transmit at another frequency out of 100,000 options, than we will not
receive it.
To overcome this I prepared a plan for a different antenna.
The antenna I thought of is a simple dipole antenna in space. This antenna
transmits and receives to all directions and is not limited to a very narrow
frequency.
In order to make it very sensitive to signals I thought to make it as long
as possible.
I found out that the solar storms make noise, and as we distance the sun the
frequency of the noise and the power is decreased.
At frequency of 50 KHz and 1 AU from the sun the noise is not significant.
At 2 AU the frequency is 25 KHz and at 10 AU the frequency we can use is 5
KHz.
The first possible antenna I thought of is a dipole, having a length of 3
Kilometers, placed as a satellite to Earth. To make this antenna and to put
it in space would not cost much and there are no risks.
It will be optimized for a frequency of 50 KHZ, but will also receive
frequencies of 20-200 KHz.
The effective area of the antenna will be 9 square kilometers. This is 100
times more than the largest antenna array on earth.
In order to detect a signal from outer intelligence, there is a need to
detect not more than 100 bits of information.  The time for this can be for
example 1 day or 100,000 second. The bit-rate will be about 0.001 bits per
second. The noise level of an amplifier for that antenna is e-21 watt per
Hz. The noise level for that need is e-24 watt.
The ratio between the communication distance and the transmitted signal in
this case is:
Distance^2            Wavelength^2            36
-----------------    =  -----------------------   =  ------   =~ e26
P transmitter           P receiver                e-24
In the case that the transmitter power is one million watts, the distance is
e16 kilometers, or about e8 AU. This is 1000 times more than the closest
star to us.
If we put the antenna more far from the sun, the temperature drops and than
the antenna wire will have lower electrical resistance. We will be able to
make it longer without increasing the weight. A 6 Kilometer antenna can be
at about 3 AU from the sun and will have the same weight as a 3 Kilometer
antenna.
If we further increase the distance from the sun, were the temperature is
below 77 degrees Kelvin, than we can use superconductors instead of a metal
wire. This will dramatically decrease the weight and enable us to use a 100
Kilometer antenna and frequency of 1.5 KHz that will increase the
sensitivity by 1000. The effective area of that antenna will be 100,000
times the area of the antenna arrays on earth.
At that frequency and distance from the Sun there is almost no noise from
plasma oscillation.
By Gil Teva 
gil...@actcom.net.il
