A Project for using the SDRplay RSPduo for EME Adaptive Polarisation with MAP65
The SDRplay RSPduo is a dual tuner SDR receiver covering 1KHz to 2GHz, it has a high stability reference oscillator which can also be locked to an external reference. These factors make it a suitable candidate for providing an affordable solution for EME adaptive polarisation.
The RSPduoEME software has been written to utilise the dual tuner capability of the RSPduo and provide a system which can be used with the MAP65 software to provide an EME adaptive polarisation system.
MAP65, written by Joe Taylor K1JT, is a Windows based wideband JT65 adaptive polarisation decoding program capable of combining the signals from orthogonal antennas to provide decoding of signals at any polarisation angle. In order to achiever this goal, the signals derived from both orthogonal antennas are required to be processed in phase with each other. Normally this is achieved by cutting the coaxial feeder lengths identically and utilising a common local oscillator signal in both down converters. Additionally, the outputs from the down converters have to be combined into a four channel (2 x 96KHz I&Q) stream to be fed into the Windows PC soundcard.
Although the RSPduo has two independent receivers derived from the same local oscillator, the starting phase of each channel is indeterminate. In order to ensure identical phase on each receiver a calibration process is necessary. At start-up the RSPduoEME software applies an identical low level calibration signal to each input and the phase error is measured. The software then corrects for this and the calibration signal is removed and in phase processing continues. The calibration process can be either automatic, utilizing an Arduino based ADF4351 calibrator, or manual. Additionally, the RSPduo and the ADF4351 can be locked to an external 24MHz reference if required. If the calibration injection point is at the antenna, the phase error caused by the coax feeders can also be calibrated out.
The RSPduoEME software is written in C++ using Qt Creator V4.6 and is intended to run under Windows 10. The application requires the RSPduo to be installed on the same computer. There are several output modes for the 96Khz I/Q data streams to allow flexibility and integration with other SDR programs such as Linrad. The UDP output is in Linrad TIMF2 format and is intended as a direct network input to MAP65. If necessary MAP65 can be run on a separate PC, providing there is sufficient network bandwidth (>10Mbs/s). If a separate SDR program is chosen, such as Linrad, there is an option for a 4 channel sound card output. Full details of the output modes available are included in the RSPduoEME User Manual along with the installation and operating instructions.
The RSPduoEME application main window is shown above which allows setting of the operating parameters and displays status messages and phase lock indication for dual channel modes. For more information and obtaining a copy of the application, please use the links above.