VSOP-2 Ground Link Station - Tracking Station Requirements - National Astronomical Observatory of Japan Y. Kono

Link system H Maser Data Storage VLBI Data Downlink Frequency GHz Bit Rate 1 Gbps Modulation QPSK TX-Power 20 W Phase Transfer Uplink Frequency 40 GHz Non Modulation TX-Power 10 W Phase Transfer Downlink Carrier wave of data downlink 2way Phase Comparison Ground Tracking Station Commanding Station TT&C Freq: 2GHz

VSOP-2 Link Function Data Transmission  Current design of observation system  Current design of downlink system Reference Phase transfer TT&C

Observation System IF-SWITCH (6 to 2 ) MOD × × × × ～ × × Synthesizer LO (36/34GHz) ～ LO (14.5GHz) ADC Observation Frequency Q-band: GHz K-band: GHz X-band: GHz VLBI DATA Rate: 512/256Msps Bit: 1/2bit Channel:2 ch Ka-TX Q-band (L) LNA Q-band (R) LNA K-band (L) LNA K-band (R) LNA X-band (L) LNA X-band (R) LNA 1024Mbps DF Intermediate Frequency GHz Base Band Frequency 1.3 GHz

ADC modes A/D bit VSOP2 A/D bit GRT BW (MHz) Quantization efficiency factor (K) Sensitivity of continuous spectrum obs (=K*√BW/128 ) No quantization ビット ビット ビット 2 ビット Gbps for Ground radio telescope capability? - GRT (2Gbps), - Correlator (mixture correlation of 1bit and 2bit )

Observation System (MOD) VLBI DATA  1024 Mbps  Telemetry data merged Modulator  Single Carrier QPSK Modulation  SiGe device  Carrier 3.4GHz & Up Conversion to 37.5 GHz

TX Amplifier Output Power 20W TWTA  Boeing, Thales, Tesat, NT-Space,,,, NT-space TWTA for a satellite 42-44GHz Output power 30W efficiency:42% 1994 New TWTA for VSOP-2 will be developed

Ka Antenna Diameter 80cm Efficiency 65 %  WaveGuide  Rotary Joint

Link Design Bit Error Rate 0.01 Ground Link Station 10m (44%)

month Rain Loss 8dB Rain loss (2 mm/hour, Height 2km)  23 dB ( Halca condition, 5 mm/hour, Height 2km)

Reference Phase transfer H Maser Phase Transfer Uplink Frequency 40 GHz Non Modulation TX-Power 10 W Phase Transfer Downlink Frequency 37.5 GHz Carrier wave of data downlink 2way Phase Comparison Ground Link Station Diameter >10m T RX <60K

Reference Phase transfer Sufficient link margin available

Summary VSOP-2 Observation System summarized Link is severe in rain condition

VSOP-2 X-band

VSOP-2 K-band

VSOP-2 Q-band

Phase characteristics of instruments H up (f) H down (f) Transponder To the Earth

VSOP-2 data transmission Why do we need GHz? Allocation of more than 1 GHz bandwidth VLBI requires wide band width for the observing sensitivity. Candidate 25.5 – 27 GHz, 37 – 38 GHz 25.5 – 27 GHz is not good because: - Closest uplink allocations are 15.3 (Secondary) or 40 GHz. - A large frequency offset between uplink and downlink leads to a problem in the compensation of the 2 way timing link in VLBI. - We cannot use same scale waveguide circuit for both up and down link signal. - It is close to the 22 GHz observing band.

Compensation error of 2 way link due to Ionosphere