Hi all,
SatNOGS DB lists UHF transmitters for DMSP 5D-3 F17 (29522) and F18 (35951) at 400.328 and 400.822 MHz (“Mode U - RTD1/RTD2”), citing eoPortal. eoPortal only describes a capability to transmit UHF RDS on these frequencies, and emitters.space lists them as “RDS service only” (RDS = 177.5 kbps BPSK). I couldn’t find any published report of anyone actually receiving or decoding it.
I looked at the six most recent Network observations vetted “good” at these frequencies (observation IDs below), and none of them show a signal I’d call consistent with DMSP:
- 13455031 (YO2CIP, F18, 400.822): clear narrow carrier, but with a residual S-curve (about -8 to +9 kHz) after Doppler correction, so it looks like a different object. Waterfall:
- 14622391 (CubeSAT-Test, F18, 400.328): several faint traces, also curving relative to the DMSP Doppler.
- 15331313 (IU0JIW, F18, 400.822): short bursts and wideband horizontal streaks, which looks like local interference.
- 14316450 (Pelt-UHF-Fixed-Yagi, F18, 400.822): many faint slanted traces, inconclusive.
- 15144067 and 15391634 (PE0SAT-12, F17, 400.822): no clear signal.
One thing to keep in mind: a 177.5 kbps RDS signal would be wider than the 48 kHz waterfall, so it would show up as a rise in the noise floor during the pass, not as a line. The default observation setup may not be able to see it at all.
Questions:
- Has anyone actually received DMSP UHF RDS, or does anyone know whether it is enabled on F17/F18?
- Should these observations be re-vetted (or the transmitters marked as unconfirmed)?
- Would anyone with a 400 MHz-capable station be willing to make a wider (~250 kHz) IQ recording around 400.33 / 400.82 MHz on a high DMSP pass? Radiosondes and cubesats in 400-406 MHz would need ruling out with a Doppler check.
Thanks!