Statement of Mission
At this Observatory we are conducting a dedicated search for weak, transient or extended in time, narrow band signals of astrophysical interest near 1.42GHz. A major problem in radio astronomy is the presence of contaminating man-made microwave/radio frequencies in the frequency region of interest, referred to as radio frequency interference (RFI). This is especially true in our case in which we expect very weak signals not associated with strong sources.
Our method of minimizing RFI in conducting this search involves the use of two radio telescopes directed skyward separated by at least 90 degrees. This method provides a distinction between signals of astrophysical interest and RFI. These telescopes use parabolic dish antennae of diameters 3 meters and 4 meters.
Internal Reports describing the 3 meter and 4 meter telescopes can be found in Internal Reports 2 and 3 respectively.
The 4 meter telescope is used to detect signals of astrophysical interest while the 3 meter telescope detects man-made microwave/radiofrequency interference (RFI). Because we expect RFI to be stronger than the weak signals detected by the 4 meter telescope, the direction toward which the 3 meter telescope is pointed is not critical except the two directions should minimize overlap of the two telescopes’ side-lobes.
When signals from both telescopes are coincident in time they are considered to be the result of RFI and the signal from the 4 meter telescope is ignored: That is, the 3 meter telescope runs interference for the 4 meter telescope.
Each telescope is fitted with its own low noise amplifier (LNA) followed by an IF (Intermediate Frequency) downconverter and computer controlled radio frequency software defined receiver. We use NetSDR radiofrequency software defined receivers manufactured by RF Space. Each is computer controlled using Spectra Vue software. Each computer/receiver performs the Fast Fourier Transform(FFT) of incoming amplitude/time signals resulting in the power frequency distribution.
Generally FFT/BLK is set to 2,097,152 and a sample speed of 1,250,000Hz thus achieving a resolution band width of 0.596Hz (frequency bin size). Absolute FFT data are stored as 2 byte custom format files.
This data is further analyzed using custom, in-house software designed by Wayne L. Buckhanan.
The power of each bin is compared with the average of nearby bins and is considered “interesting” if it exceeds the nearby average by a user selected number of standard deviations from the mean. Each such data point is time stamped and the corresponding celestial coordinates of Right Ascension and Declination toward which the telescopes are directed are computed.
Additional criteria placed on data points for them to be considered interesting from both telescopes are: A. Adjacent-in-time data points must not be separated in time by more than a preset time interval. B. Adjacent-in-frequency data points must not differ by greater than a preset value. C. The duration of a series of interesting data points must continue for a minimum of some preset time span. D. Finally both time and frequency constraints are placed on the signals from both telescopes in the determination of whether their signals are or are not coincident. If such a set of interesting events from the 4 meter telescope survives the above criteria it is considered worthy of interest only if it is not accompanied by the same signal in the 3 meter telescope
All data, approximately 2 million data points per second, are analyzed in real time using local computers in tandem with distance servers (Linode) . Data is returned from the distance servers and results are finally presented in the form of 3-dimensional graphs of the number of Interesting Events and their powers versus Local Sidereal Time, frequency, Right ascension and Declination.
Empirical results will be compared to theoretical predictions now under development.