RAL10PL is a microwave receiver designed to be installed outside, in proximity of the antenna system, in areas without operators, to build a remotely controlled radio telescope.
The instrument is assembled inside a strong box in polycarbonate, resistant to rain and humidity. RAL10PL communicates with the outside world via an Ethernet port that allows the network connection of the plant and its monitoring also through the web. The main (and only) feature of this receiver is the ability to manage an equatorial mount (of the type used for optical astronomy tools, well known to amateur astronomers) for the handling of the radio astronomic antenna. The serial port of the frame (usually RS232 type) can be connected to the RAL10PL and conveyed through a single Ethernet cable to the station PC.
RAL10PL is a very robust radiometer, conceived and designed for remote radio astronomy facilities, not controlled by operators. The unit is composed of a sturdy plastic box that contains the thermo-stabilized receiver and the power supply. The tool receives the RF signal coming from the external LNB (the ideal is RAL10_LNBB, equipped with an internal temperature control, if you wish to create a radio telescope operating in the band 10-12 GHz) and the RS232 serial channel from the movement system of the antenna: an Ethernet port ensures the instrument communication with the station PC. You can manage RAL10PL via the Internet by developing a dedicated web page. In the bottom right you can see the '22 dB Attenuator RAL164 useful when observing intense radio sources like the sun. To optimize the stability of the radiometer, inside the receiver an automatic PID control is implemented that maintains the electronics temperature constant.
Inner panel of the receiver RAL10PL.
The previous image shows the block diagram of a radio telescope that uses the RAL10PL receiver. Although it is indicated a reception band 10-12 GHz (the most common one, given the availability of the TV-SAT accessories in our zones), you can use LNB (and relative antenna) with any input frequency, as long as the output frequencies they are included in the reception "window" accepted by RAL10PL.
It is also possible to construct a direct amplification radio telescope, without using frequency converters (LNB), but a chain of low noise amplifiers and bandpass filters. Of course, taking into account the antenna used, is necessary to ensure sufficient amplification for a correct detection of the received signal, together with a suitable filtering to minimize interference.
The radio signal captured by the antenna, amplified and converted in frequency by the external LNB unit (Low Noise Block Converter), is transmitted through a coaxial cable to the RAL10PL that measures its power. The level of the detected signal is adapted to the acquisition dynamics of the internal analog-digital converter that converts the analog radiometric information into numerical data suitable for further processing with the station PC.
In a Total-Power radio astronomy receiver, the measure involves the acquisition of small variations in the signal received due to radio source, superimposed on an almost-constant component, of much greater magnitude, introduced by instrumental noise. To evaluate only the "useful" signal you must subtract from the detected signal the contribution due to the background noise: an offset voltage REF_BASELINE is therefore generated, that serves to position the level of the base line radiometric at a suitable point of the acquisition scale.
RAL10PL, run by a couple of microprocessors, processes the detected signal, sets the reference for the base line, the post-detection gain and the constant of integration of the measure, provides for the formation of the serial data packet for the communication with the station computer and stabilizes the internal temperature.
Throught a Ethernet port you can remotely control the instrument.
These characteristics classify RAL10PL as an ideal tool to meet any installation need for a semi-professional amateur radio telescope, not served by operators.
Transits of the radio source Taurus A (M1) registered with RAL10PL and the RAL230ANT antenna system. The transit technique is to identify the radio source to observe, orient the telescope in the sky area affected by its passage in the near future (for example, 30 minutes later) and stop the radio telescope in that position. Because of the apparent rotation of the sky (produced by the Earth's rotation), the object will move to the area of the sky "watched" from the antenna and will be intercepted by the receiving beam. In this experiment five consecutive transits of the same area of the sky were scheduled, each 4 degrees large: calculating the mean value of the 5 transits (red trace) random noise reduces and the visibility of the radio source increases.
Transits of the radio source Cassiopea A registered with RAL10PL and the RAL230ANT antenna system. Cassiopea A is a "nearly punctiform" object, often used by radio astronomers as a sample radio source to verify the characteristics of the receiving diagram of a radio telescope. An important instrumental parameter that can be calculated by observing an object as Cassiopea A is the so-called HPBW (Half Power Beam Width) that is the width at half power of the antenna main lobe (expressed in degrees). The following formula is used:
where t is the transit time of the radio source in minutes and δ is its declination in degrees. Analyzing the recordings shown in the figure (orange track that represents the average calculated on 5 consecutive transits) we can see how the time taken by Cassiopea A to cross the two half-power points (indicated by the vertical lines) is about 6 minutes. Considering its declination of δ=59°, the calculation provides:
agreeing with the value HPBW=0.8° obtained by the antenna model RAL230ANT used in the project simulations.
RAL10PL Technical features
- Dimensions: about [300L, 180H, 300W] mm, IP65.
- Weight: about 3.9 kg
- Input Band: 1100-1600 MHz.
- Typical gain of the RF section: 36 dB.
- Input impedance (F-connector): 75 Ω.
- LNB power supply through coaxial cable, protected by fuse
- Quadratic Detector, temperature compensated for the measurement of the RF signal power.
- Setting of the offset for the radiometric baseline.
- Automatic calibration of the radiometric baseline.
- Programmable time constant of the integrator: from about 0.1 to 113 minutes.
- Programmable gain in post-detection voltage: from 42 to 1008 in 10 steps.
- Acquisition of the radiometric signal with 14-bit ADC.
- Nr. 2 microprocessors for system management.
- Visualizations: Power ON (GREEN Led), Command ON (RED Led), Controllo di temperatura (YELLOW Led)
- Ethernet communication port for the proprietary protocol (dedicated control web page implementable).
- Manages the serial communication port RS232 for the antenna motorization system.
- Stabilizing of the internal temperature with PID PWM regulator (about 44°C) and protection for the maximum temperature.
- External power supply: 12 VDC – 2 A min.
- General power supply protected by fuse
- LNB power supply through coaxial cable, protected by fuse
- Power supply: Input: Network 85-264 VAC / 47-63 Hz, 60W, Output: 12 VDC/2A max. for the RAL10PL receiver; Output: 12 VDC/ 3 A max for the antenna motorization system