TacSat-4
TACSAT-4 is a technology demonstration satellite launched by the Naval Research Lab in the USA. The satellite, catalogue 37818 was launched on the 27th September 2011. From research and off air monitoring, the satellite carries 10X UHF transponders compatible with existing UHF satcom transceivers, 1X MUOS 5MHz wide transponder, 1X 401MHz transponder for ocean data collection (store / forward), one X-Band transponder operating in the standard military band and 1X S-Band TT&C downlink operating on 2206.120MHz. Data and FFT's on this page from blh, zguy, phil and pjm.
| Downlink | Frequency MHz | FFT |
|---|---|---|
| UHF | 249.600 (FFT thanks to blh) This TPX carries a relay of a spanish radio station |
 |
| UHF | 252.950 (tnx zguy)
(FFT thanks to blh) |
 |
| UHF | 253.000 (FFT thanks to blh) |
 |
| UHF | 254.125 - 40KHz b/w (FFT thanks to Phil) |
 |
| UHF - MUOS | ||
| UHF - ODTML | 401 +- | |
| S-Band | 2206.120 |  |
So far the only downlink that has been detected on a repeatable basis is the S-Band TT&C. UHF so far seems to be activated when over Blossom Point satellite ground station. The initial acquisition of the Telemetry was one day after launch, and as such it could not be 100% positively identified. The FFT of the initial signal is shown below;
Interesting documentation received at UHF-Satcom.com regarding TacSat-4 payloads - this paper looks to be from a conference on satcom. Click on the small images for the full resolution scan. The most interesting point to note is that TacSat-4 appears to have a precision ground based radio location system, and although some of the actual precision figures have been blacked out, one screenshot shows an 'uncertainty of <0.5 miles' - mention is also made of 'less than 500ft after several minutes' - if this really is the case, lets hope its the beginning of the end of pirate use of UHF satellites!
