Implementation of Open-Loop Radio Frequency Record Feature on the Johns Hopkins University Applied Physics Laboratory Frontier Radio

The Johns Hopkins Applied Physics Laboratory (JHU/APL) Frontier Radio (JHU/APL FR), as flown on the Van Allen Probes and Parker Solar Probe missions, is a deep space communications platform designed to minimize size, weight, and power (SWaP) while maximizing radiation tolerance. This platform has historically only been used to support Deep Space Network communications and modulation formats. The receive chain was designed to support subcarrier PCM/PM waveforms and only forward demodulated symbols and uplink packets over to avionics. For the Europa Clipper mission, there was a desire to be able to record arbitrary segments of spectrum for post-processing on the ground, due to the real-time processing limitations of the low-SWaP JHU/APL FR. Therefore, a open-loop recording feature was added to the JHU/APL FR. The feature requirements dictated minimal firmware development, no additional hardware, and a packet stream to avionics using the existing spacewire interface. The open-loop record feature has differing bandwidths, ranging from the highest supported by spacewire to an eighth of that rate in order to capture as much data as possible or to reduce data volumes. The user can steer the center frequency of the recording window in order to capture a certain slice of spectrum. A simple post-processing algorithm was developed to fix a slight temporal shift during the recording data signal chain. An overview of the firmware design, algorithms, post-processing procedure, and analysis of the results are described below.