Giga-bit VLBI, Progress on Giga-bit Sampler

Junichi Nakajima(nakaji(AT)

Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-0012, Japan

1. Status

Giga-bit samplers (see Figure 1) were tested at the Nobeyama radio observatory (see the previous issue of TDC news for details of the VLBI giga-bit sampler). Both CRL-VLBI and NRO-spectrometer group carried out the test. The DSO (Digital Sampling Oscilloscope) sampler consists of a modified DSO part and an interface for successive processor. The interface unit is working as a de-multiplexer of the data stream for each purpose. Nobeyama 25-multi-beam receiver for 45m radio telescope will use the DSO sampler with 1 Gsps (sampling per second) 2-bit 4-channel. Although there is a difference in the interface unit channel configuration, we agreed to unify the DSO sampling part. This will simplify the maintenance procedure at the manufacture. Radio astronomical society will be able to accommodate each other with sampler on site. In September whole astronomical giga-bit sampler had been gathered at Nobeyama. We measured all DSO sampler at the same bench. Several static and dynamic parameters to evaluate AD performance had been measured. Table 1 shows the unified astronomical sampler major specification.

Figure 1. TDS784A Gigabit samplers under test.

Table 1. TDS-spec Comparison between the VLBI & Spectrometer.
.VLBI Spectrometer
(TDS784 modified)
Sample rate(M) 1024/512/256 1024/512/256
Channel Input 4/4/4 (*1) 4/4/4
AD Quantaization 2 2
Output Datarate 128MHz x64 128MHz x6
Total Datarate 8Gbps 8Gbps
Input Datarate 128MHz x64 128MHz x64
Handle rate(M) 1024/512/256 1024/512/256
Select channels 1/2/4 4/4/4
Quantaization 1 or 2(*2) 2
Output connector D-Sub SCSI-halfpitch
Total datarate 2Gbps 8Gbps
Instrument Recorder Auto-correlator
Datarate 1Gbps (x2) (*2) 2Gbps (x4)
Notes: 1:unified version. 2:single recorder use MSB bit only.

2. Measurement

Each channel of the sampler works 1024 Msps 2-bit for scientific data sampling. We have checked AD performance. Although the TDS784 is completed as the time-domain measurement instrument, longterm frequency-domain AD characteristics should be examined for astronomical purposes. We have measured following parameters for the first step .

Updated on November 20, 1997. Return to CONTENTS