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

Ts4 249600
UHF 252.950 (tnx zguy)

 (FFT thanks to blh)

Ts4 252950
UHF 253.000

 (FFT thanks to blh)

Ts4 253000
UHF 254.125 - 40KHz b/w

 (FFT thanks to Phil)

Ts4 254125
UHF - MUOS
UHF - ODTML 401 +-
S-Band 2206.120 Ts4 sband 031011

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;

Ts4 sband 280911

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!

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