Doppler-Attributed Wideband Emission Near GPS L1 from HJS-7C (2025-209C)

This IQ recording captures a strong wideband emission in the GPS L1 region associated with HJS-7C / NORAD 65619 / COSPAR 2025-209C, a Chinese LEO payload launched on 2025-09-16 from Jiuquan. Public catalogue sources list HJS-7C as an active Chinese payload in a near-circular orbit of roughly 1100 km altitude, 50° inclination, and 107.3 minute period. The recording was made as part of a physical-layer audit of the GPS L1 channel using a 1.5 m dish, a tuned ~1575 MHz feed, LNA, and front-end filtering and a Rb reference with GPS disipline. The Doppler fit was performed using a strong spectral component near the GPS L1 channel centre as the tracking feature. This component is associated with the broader wideband emission observed during the pass of HJS-7C and provides a clear Doppler curve suitable for attribution. The fitted feature is near 1575.393020 MHz, about 26.98 kHz below nominal GPS L1 at 1575.420000 MHz. The timing, Doppler behaviour, and beam-crossing profile are consistent with HJS-7C as the emitting source, and the recording demonstrates that LEO/high-LEO objects can produce detectable wideband activity in the GPS L1 neighbourhood. The recording is provided as GQRX raw complex baseband IQ data: 32-bit floating point, interleaved I/Q, little-endian, sampled at 6.000 MS/s with a nominal centre frequency of 1,575,419,998 Hz.