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

Y. Kono

Link system

H Maser Data Storage

VLBI Data DownlinkFrequency 37-38 GHzBit Rate 1 GbpsModulation QPSKTX-Power 20 W

Phase Transfer UplinkFrequency 40 GHzNon ModulationTX-Power 10 W

Phase Transfer DownlinkCarrier wave of data downlink

2way Phase Comparison

Ground Tracking Station

Commanding Station

TT&CFreq: 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-S

WIT

CH

(6 to 2 )

MOD

×

×

×

×

～

×

×Synthesizer

Synthesizer

LO(36/34GHz)

～LO(14.5GHz)

ADC

ADC

Observation FrequencyQ-band: 41 - 45 GHzK-band: 21.5- 23.5 GHzX-band: 8.0 - 8.8 GHz

VLBI DATARate: 512/256 MspsBit: 1/2 bitChannel: 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

DF

Intermediate Frequency6.6- 8.8 GHzBase Band Frequency1.3 GHz

ADC modesA/D bit

VSOP2

A/D bit

GRT

BW

(MHz)

Quantization efficiency factor (K)

Sensitivity of continuous spectrum obs (=K*√BW/128 )

No quantization

No quantization

128 1 1

2 ビット 2 ビット 128 0.88 0.88

1 ビット 1 ビット 256 0.63 0.90

1 ビット 2 ビット 256 0.75 1.06

2Gbps for Ground radio telescopecapability?- 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 satellite42-44GHzOutput power 30Wefficiency:42%1994

New TWTA for VSOP-2 will be developed

Ka Antenna

Diameter 80cm Efficiency 65 %

WaveGuide Rotary Joint

Link DesignData Downlink Fine Condition 0mm/ h（ ）Rain Condition 2mm/ h（ ）

Frequency Hz 3.8E+10 3.8E+10Transmitting Power dBm 41.0 41.0 W (- 2dB Back Off on Downlink) 20.0Feed Loss dB - 5.5 - 5.5Antenna Gain dBi 48.1 48.1 80cm*0.65EIRP dBm 83.6 83.6Pointing Loss dB - 0.4 - 0.4Space Loss dB - 213.6 - 213.6 Distance(km) 30000.0Rain Loss dB 0.0 - 8.0Atomospheric Loss dB - 1.9 - 2.2Polarization Coupling Loss dB - 0.2 - 0.2Antenna Gain dBi 70.0 70.0Pointing Loss dB - 0.4 - 0.4Feed Loss dB - 2.0 - 2.0Received Power dBm - 64.9 - 73.2System noise temperature dBK 21.5 24.7 Tsys=140KNoise power spectral densitydBm - 177.1 - 173.9C/ N0 (achieved) dB 112.2 100.7C/ N0 (Required) dB 98.5 98.5 1024MbpsLink Margin dB 13.7 2.2

note

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)

Rain Loss

0.005.00

10.0015.0020.0025.00

0 1 2 3 4 5

Rainfall (mm/ h)

Rai

n Lo

ss (

dB)

Reference Phase transfer

H Maser

Phase Transfer UplinkFrequency 40 GHzNon ModulationTX-Power 10 W

Phase Transfer DownlinkFrequency 37.5 GHzCarrier wave of data downlink

2way Phase Comparison

Ground Link Station Diameter >10mTRX <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

Hup(f) Hdown(f)

Transponder

To the Earth

VSOP-2 data transmissionWhy do we need 37-38 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