Project - BSA LPI

In 2010-2012, the Large Phased Array was upgraded, as a result of which four independent radio telescopes were actually created on the basis of the old antenna field, two of which (LPA-1 and LPA-3) were commissioned in 2013-2014.

128 non-switchable beams were created in the BSA-3 radio telescope. These rays overlap declinations from -8° to +55°. They are serviced by three registrators. The overlap of the beams is made at a power level of 0.4. The effective area of the BSA-3 brought to the zenith is 47000±2500 m². The full reception bandwidth is 2.5 MHz.
 

Sensitivity changes depending on the direction in the sky:

Since the BSA-3 beams are fixed and the antenna field is stationary, the sensitivity of the antenna varies greatly in different directions.
The figure shows the declination along the horizontal axis, and the sensitivity from the maximum possible value, taken as one, along the vertical axis. It can be seen from the figure that if the source is positioned incorrectly in the sky, the difference in sensitivity can vary by 8-9 times.
 

To calibrate the power of incoming signals, a signal from a special (noise) generator is applied to the input of low-noise amplifiers (LNA). This signal provides a measurement of the main parameters of the radio telescope:

• system noise temperatures,
• the effective area of the antenna,
• performance checks of the distributed reinforcement system and its individual elements.

The LNA input switches between the antenna and the calibration noise generator. The noise generator generates two calibration signal levels corresponding to the noise temperature of the matched load and the noise temperature of the switched-on generator. The noise temperature of the matched load is equal to the ambient temperature. The temperature of the noise signal of the calibration generator is 2400 K, and it does not depend much on the ambient temperature. The measured step size changes do not exceed ±3% when the ambient temperature changes from -15°C to +43°C.
 

Map of the area observed in the sky in one day:

The figure shows Moscow time (+4 UT) on the horizontal axis, and the observed declination on the vertical axis. The map is made in temperature units. The Galactic plane, the North polar spur, and strong radio sources are visible. For strong radio sources, the side lobes of the LPA are visible along the declination axis. These are false sources located at distances of about 7° from the main source.
 

The digital radiometer is an industrial computer with multi-channel receiving and recording modules. Three digital radiometers provide signal registration for 128 beams of the radio telescope. Each recorder includes 8-channel digital signal processing modules. Four paired analog to digital converters TI ADS62P29 are installed at the input of the module.

Digital processing is performed using programmable logic integrated circuits — FPGA EP3SL780C3 (Stratix III, Altera). Used:

• the method of direct digitization of the signal,
• digital filtration systems,
• frequency transfer,
• spectral analysis.

The digitization frequency is 230 MHz,
the band of the recorded signal in each channel is 2.5 MHz,
the central frequency is 110.25 MHz.

FPGA resources allow you to implement on a single chip:

• 8 independent video converters,
• filtering of high-frequency and low-frequency signals,
• spectral analysis and processing of 8 independent data streams.

The recorder module has the ability to write to a hard disk:

• signal power in 32 spectral channels with a frequency resolution of 78 kHz,
• signal power in 6 spectral channels with a frequency resolution of 415 kHz.

The time resolution of the signal is 12.5 ms or 100 ms.

The time service is monitored at the beginning of each observation hour. The first point is digitized with an accuracy of at least 5 ms. The accuracy of polling channels within an hour is determined by the accuracy of the digital receiver's quartz frequency generators. The estimated maximum possible time difference in the hourly interval is:

• 25 ms (± two points of primary «long data»),
• 100 ms (± one point of primary «short data»).

Simultaneous data recording has been carried out since August 2014:

• with a constant 100 ms in 6 frequency channels («short data»),
• with a constant 12.5 ms in 32 frequency channels («long data»).

The total amount of data accumulated by the end of 2024 exceeds 350 terabytes.