GRAPE 1 DRF (Doppler Radio Frequency Receiver for the Great Radio Amateur Propagation Experiment) is a citizen science instrument that receives HF time-standard signals (e.g., WWV, WWVH, CHU) to measure Doppler shifts caused by ionospheric dynamics. Data is collected by volunteers using software-defined radios and GPS-disciplined oscillators, recorded in Digital RF (DRF) format, and contributed to the HamSCI Personal Space Weather Station (PSWS) repository for space weather research.

The AB4EJ G1DRF station is located at 33.375ºN, 87.583ºW. Instrument type is Grape 1 DRF. There is one antennas at this station, which is Antenna 1: 80 m dipole. It records 10MHz Doppler Shift.