## 4 New Electronic Control System of the Receiver for the Installation on SRT
### Mixer Tuning and Receiver Calibration Block  
The mixer tuning and receiver calibration block is composed of two electronic boards, both controlled by a single Arduino UNO REV3 microcontroller. Only one microcontroller is enough to handle the signals and functions of these two electronic devices. These boards are fundamental to calibrate the ex-PdBI receiver, evaluating its noise temperature, and for tuning its operating frequency. In particular, these two electronic devices are (see Figure 7a):  
* The SIS mixer backshort motor control board;
* The receiver calibration motor control board. The embedding impedance the SIS mixer due to its integrated superconducting circuitry in the waveguide structure is frequency-dependent. A suitable mixer tuning is obtained by adjusting the length of the waveguide section between the SIS junction block and the backshort (see Figure 7b). IRAM developed a system, devoid of onboard intelligence, based on a DC motor with a potentiometer for backshort regulation (moving forward or backward) with respect to the junction (see Figure 8a). Highly accurate positioning results can be achieved by supplying short pulses to the motor. This IRAM board was placed at the top of the device to control the motor displacement. A new electronic board has been developed to remotely control the IRAM board (Figure 8b). This new board,  
Figure 6: (**a**) SIS mixer junction bias module developed at IRAM. (**b**) Three-dimensional rendering of the SIS mixer biasing control board developed for SRT. Figure 7: (**a**) Mixer tuning and receiver calibration block, composed of the SIS mixer backshort motor control board and the receiver calibration motor control board. (**b**) Inner waveguide structure of the SIS mixer showing the movable backshort and the mixer chip [32; 33]. named an SIS mixer backshort motor control board, features a power supply block, readout block, and motor control block. The board is managed using a second Arduino UNO REV3 microcontroller [43]. The readout block is equipped with a high-resolution ADC, model ADS1115, fitted on Adafruit modules from Texas Instruments [44], for the evaluation of the backshort motor position based on reading its voltage values. The motor control block allows adjustment of the potentiometer using digital commands to position the backshort of the mixer at the desired position. As explained in Section 2, the ex-PdBI W-band receiver is equipped with a classical calibration system based on the cold and ambient load method. The cryogenic and room temperature loads are installed on their respective DC motors, which allow their correct positioning for receiver calibration. The control system for the management of the receiver calibration block requires switching from two available positions for the DC motor: calibration on and calibration off, respectively. These features are provided by the motor position with respect to two inductive proximity switches: the first for the rest position (i.e., calibration off) and the second one for the working position (i.e., calibration on). IRAM developed an electronic board for the execution of these operations (see Figure 9a) devoid of onboard intelligence, and the remote control is unavailable. Therefore, a new receiver calibration motors control board, equipped with a power supply stage and a motor control stage, was developed (see Figure 9b). The motor control stage permits moving the DC motor between the two working positions (i.e., calibration on and calibration off positions) and collecting information about its state. Figure 8: (**a**) IRAM backshort system. (**b**) three-dimensional rendering of the SIS mixer backshort motor control board developed for SRT. Figure 9: (**a**) IRAM board for the management of the calibration system; (**b**) 3D rendering of the new control board for the calibration motors developed for SRT. A dedicated module of Tester100 GHz was developed to control and test the mixer tuning and receiver calibration block.