KVN and VERA Array (KaVA)

Digital Signal Process

In VERA system, A/D (analog-digital) samplers convert the analog base band outputs of 0-512 MHz x 2 beams to digital form. The A/D converters carry out the digitization of 2-bit sampling with the bandwidth of 512 MHz and the data rate is 2048 Mbps for each beam.

In KVN system, A/D samplers digitize signals into 2-bit data streams with four quantization levels. The base band output is 512-1024 MHz. The sampling rate is 1024 Mega sample per second (Msps) with 2-bit sampling resulting a 2048 Mbps=2 Gbps data rate at 512 MHz frequency bandwidth. Four streams of 512 MHz band width (2 Gbps data rate) can be obtained in the KVN multi-frequency receiving system simultaneously, which means that the total rate is 8 Gbps.

Since the total data recording rate is limited to 1024 Mbps (see the next section), only part of the sampled data can be recorded onto magnetic media. The data rate reduction is done by digital filter system, with which one can flexibly choose number and width of recording frequency bands. Observers can select modes of the digital filter listed in the Table 6 For the 2016A KaVA observing season, four digital lter modes are available. From the 2016A season, a new digital filter mode called VERA4S is also available (Table 7). In VERA7SIOS mode in the Table 6, two transitions (v = 1 & 2) of SiO maser in the Q band can be simultaneously recorded.

Table 7:New Digital filter mode for KaVA.
Mode Rate Num. BW/CHb Freq. ranged Side
Name (Mbps) CHa (MHz) CHc (MHz) Bande Notef
VERA4S* 1024 8 32 1 128-160 U
2 160-192 L
3 192 - 224 U
4 224 - 256 L
5 256 - 288 U
6 288 - 320 L
7 320 - 352 U
8 352 - 384 L
* All channels are for A-Beam (VERA) and LCP (VERA/KVN). Mode names are tentative.
a Total number of channels
b Bandwidth per channel in MHz
c Channel number
d Filtered frequency range in the base band (MHz)
e Side Band (LSB/USB)

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KaVA ( KVN and VERA Array )