RAL10MW: TOTAL-POWER MICROWAVE RECEIVER
RAL10MW is a compact and flexible, high-performance microwave radiometer developed for applications in radio astronomy, environmental remote sensing and atmospheric systems. It can also be used in medical and industrial sectors. The receiver can operate in Total-Power or Dicke-Switch mode. Even if the most common use of the RAL10MW radiometer is expected with antennas and external units (LNBs) for the 10-12GHz satellite TV band, the instrument is perfect as the final stage of a receiver also operating at other frequencies, if preceded by amplifiers-converters specific for a given reception band.
Irrespective of the operating mode chosen for the tool (full power or switching radiometer), the accuracy and repeatability of the measurements are achieved by thermally stabilizing RAL10MW through the PID automatic control. Obviously, the combination of switching radiometric stabilization technique with temperature control guarantees the best performance.
The structure of the radiometer is conceptually simple: basically, it’s a radio frequency bandpass amplifier followed by a precision detector with quadratic characteristic and wide dynamics that calculates the noise power associated with the received signal, integrated within the bandwidth of the device. The radiometer doesn’t perform frequency conversions and directly detects signals within its bandwidth.
The previous image shows the block diagram of a radio telescope using RAL10MW radiometer.
The block on the left represents a generic LNB outdoor unit, complete with illuminator, assembled on the focal point of a parabolic reflector antenna commonly used for TV-SAT reception. The intermediate frequency signal 950-2250 MHz from the outdoor unit is transmitted to the RAL10MW radiometer through a 75 Ω coaxial cable, amplified and processed by the receiver, transmitted to the station PC through a USB serial port.
To minimize the effects of external interference, it is advantageous to limit the bandwidth of the system around the 1420 MHz frequency, reserved for radio astronomy research.
The program for the station PC, supplied with the radiometer, specific for automatic acquisition and control of the RAL10MW radiometer, is the RAL10MW_DataLogger, a basic and easy to use program.
The program controls all the operating parameters of the instrument, allows you to view the progress of the measurements over time and to store the data in a text format file, easily usable for subsequent processing. The variations of the acquired radiometric data are displayed on the graphics window as moving traces of different colors: in a rectangular diagram, the abscissa is the time variable (expressed in UTC time) and the ordinate is the intensity of the signals expressed in relative counting units [count] if the instrument has not been calibrated, or in [K] (equivalent antenna temperature) if the instrument has been calibrated.
In this example, the program RAL10MW_DataLogger is set to operate the radiometer in DICKE-SWITCH (switching radiometer) mode. The graphics window shows the tracks (with different colors, if enabled) representing the radiometric signals ANT (blue TOTAL-POWER trace when the radiometer input is connected to the antenna), REF (black REFERENCE trace when the radiometer input is connected to the thermally stabilized resistance) and the radiometric response RADIO=ANT-REF+BASELINE (red trace). If the instrument is set as a total power radiometer (TOTAL-POWER mode), the graphic tracks of the REF and RADIO signals will converge to the ANT signal as a single track, while if the instrument is set to REFERENCE mode, the tracks of the ANT and RADIO signals will converge to the REF signal.
RAL10MW Technical features
- Dimensions: L= 200 mm, H= 100 mm, D= 155 mm.
- Weight: about 1.5 kg.
- Input frequency band: 1377 – 1444 MHz.
- RF input: F-type connector, impedance 75 Ω.
- Precision square detector circuit for measuring RF signal strength.
- Offset setting for radiometric baseline.
- Automatic radiometric baseline calibration and control.
- Programmable post-detection voltage gain.
- Programmable integration constant.
- Storage of the receiver operating parameters in the internal memory.
- Measurement of radiometric signal and internal temperature: ADC 16 bit.
- Radiometer operating modes (only for prepared LNB): TOTAL-POWER, REFERENCE, DICKE-SWITCH.
- Receiving polarization selection for external LNBs (TOTAL-POWEr mode only).
- Selection of the reception band for compatible LNB (tone 22 kHz).
In the standard configuration, the 22 kHz tone for receiving band switching and the selection signal for receiving polarization or antenna/reference switching when the radiometer operates in DICKE-SWITCH mode (only for preparede LNBs) are sent to the outdoor unit via the coaxial cable. On request, it is possible to have the switching signal on an independent connector (switching frequency about 4 Hz).
- Radiometer control with microprocessor.
- Internal temperature control with PID regulator (programmable from 40 to 55 °C).
- Calibration procedure of the measurement scale in equivalent antenna temperature [K] after entering the storable calibratin parameters.
- USB serial communication port with proprietary protocol.
- Power supply: 85-264 VAC / 47-63 Hz, 36W.
- Low voltage supply: 12 Vdc from external source (battery).