How We Do It?
As mentioned earlier, the Boonah Space Centre will primarily concentrate on radio astronomy type observations using up to 4 specially constructed radio telescopes. The 2 largest ones will be 42 feet (14mtrs) in diameter and be supported by towers and equatorial mounts originally used at the CSIRO's Solar Radio Heliograph array that was constructed at the Culgoora Observatory (Narrabri NSW). This site now hosts the ATNF Compact Array which is similar to The Very Large Array Socorro New Mexico.
The 42 foot dishes were moved onto the site in May 2000 where they have been sitting ready for re-assembly but we will not be mating the dishes to the Heliograph equatorial mounts for some time. Refurbishment and upgrade of the mounts is necessary so that they will handle the increased loads from the larger dishes. We are working hard to prepare the two dishes so that they can be assembled and mounted on three Acro Props just above the ground in "bird bath" mode. This will allow us to get the electronics installed and tested prior to eventual mounting on the towers. The two 42 foot dishes used to form part of a microwave communications network around Queensland for Powerlink, who is responsible for the power distribution throughout the state. We are very grateful for the assistance that Powerlink has given us, especially the 2 large dishes that will form the heart of our array.
The third dish is an
Commscope (formerly Andrew's) 5mtr (15 foot) solid
cassegrain type antenna which will host two receivers mounted 90 degrees out of phase with each other. These two separate receivers will look at signals from the same wave guide at separate
Polarization (vertical / Horizontal) simultaneously over a 500 MHz slice from 11 GHz to 11.5 GHz When operational we will be concentrating on a range of frequencies starting at the Hydrogen Line (1420.405mhz) and extending up to 1668 MHz. Our Equipment will be capable of the simultaneous Analysis of 80 million 0.5htz channels in blocks of 10 MHz.
Each of the 4 receivers will provide a 10 MHz "chunk" of the radio spectrum that will be fed into the DSP for analysis. The 11 GHz system will be set to take The signals from the LNC down converted o 960 ~ 1460 MHz and analyzed in a similar manner as the rest of the systems One of our founding members,
Mr. Neil Boucher, has indicated that he will provide the Institute with a state of the art
Digital Processing System (DSP) that will become the heart of the SETI detection system. The signals from the high gain low noise amplifiers (which are mounted on the dishes) will be fed into a 4 way splitter and then on to the four receivers that will be monitoring their respective section of the waterhole (1420mhz).
Each of the DSP's will be fed the 10MHz wide signal outputs and perform the analysis of what is received. A bank of Pentium computers running software especially designed to look for the signals that we think are buried in the cosmic noise. We will monitor progress on waterfall type displays and record what is interesting. Other software will manage the rest of the analysis systems so we can look back over our data and perchance find something that we may have missed on a previous run.
Our software will be searching for signs of extremely weak narrow band signals that could only come from a non-natural source. A transmitter that created the signal artificially and probably produced by another civilization. Because we expect the signals to be very week, we must employ sophisticated mathematical algorithms to detect and amplify the signals that can filter them using ingenious statistical methods. The software will perform a
Fourier Analysis on the static, trying to find those telltale signs of artificiality indicating that we may have detected the signal we have been searching for. Computer programs will monitor the output for frequency drifts that may indicate the transmitting source has a velocity, through space, compared to the receiving antenna. If the frequency shift is in an upward direction (increasing) we can say that the source is moving toward us (blue shifted). If the frequency shift is going down (decreasing) we can assume that the source is receding from us (red shifted). This effect is known as
DOPPLER SHIFT and is one of the most powerful tools used by both Radio and Optical Astronomers. There is a natural Doppler shift caused by the Earth's movement through the Solar System and also the Sun's movement through interstellar space and also the motion of the Galaxy. This motion causes an interesting frequency shift to be applied to any signal being received from on the Earth. The algorithms used to computer the shifts in frequency due to the accumulation of all these motions is very complicated but thankfully, science has worked out the math's long ago to do this. The known frequency shift can be used as a tool to extract useful information about any potential received signal. By subtracting these effects caused by our motion through space we can pinpoint the position of a candidate signal and attempt to identify its apparent position in space. I would think that another civilization would send the signal without any frequency correction at all. This would allow us to discover certain information about the source of the signal. ie whether it is a fixed source in space or on a planet.
Radio Astronomers use these effects to measure the velocity of objects moving through space. This helps us obtain many useful facts about what is happening in and around strange, exotic objects like Black Holes, Super Novas and other little understood phenomena that exist in the far reaches of the universe. We use the Doppler Shift to help decide if a detected signal is coming from a satellite or just local interference from the Microwave oven next door. The art of Radial Velocity measurements as performed in the field of optical astronomy is similar to the Doppler shift experienced in radio astronomy. That characteristic CHIRP with a sliding frequency may be the signature of the signal we have been waiting for.