The NRO45 covers an observing frequency range of 20 – 116 GHz with multiple receivers. The VLBI backend system of the NRO45 is currently equipped at K-band and Q-band. Figure 4 illustrates a ﬂow diagram of the VLBI receiving system in the NRO45. The observable RF range and typical receiver noise temperature for the receivers at K- and Q-bands are also summarized in Table 4. The received RF signals are down-converted into an IF range of 5 – 7 GHz, and the IF signals are then mixed down to the base band of 512 – 1024 MHz, which is the input to the A/D sampler.
|Driving axis||Driving range||Max. driving speed||Max. driving acceleration|
|AZa||-60◦ ~ 510◦||0.3◦/sec||0.3◦/sec2|
|EL||12◦ ~ 80◦||0.3◦/sec||0.3◦/sec2|
|AZa||-60◦ ~ 425◦||0.5◦/sec||0.27◦/sec2|
|EL||8◦ ~ 88◦||0.3◦/sec||0.16◦/sec2|
|AZa||-90◦ ~ 450◦||2.1◦/sec||2.1◦/sec2|
|EL||5◦ ~ 85◦||2.1◦/sec||2.1◦/sec2|
|FRa||-270◦ ~ 270◦||3.1◦/sec||3.1◦/sec2|
|AZa||-90◦ ~ 450◦||3.0◦/sec||3.0◦/sec2|
|EL||5◦ ~ 85◦||3.0◦/sec||3.0◦/sec2|
aThe north is 0◦ and the east is 90◦.
bFR is 0◦ when Beam-1 is at the sky side and Beam-2 is at the ground side, and CW is positive when an antenna is seen from a target source.
Currently, one of the receivers can be selected by switching the mirrors in the optics in a few minutes manually. In the near future, K- and Q-band observations can be conducted simultaneously by inserting a perforated high-pass dichroic plate. When using the dichroic plate, the gain of the Q-band signals may be reduced by 0.3dB (in 2018 June), causing the rise of the system noise temperature by about 30 K.