Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The S2 VLBI Correlator: A Correlator for Space VLBI and Geodetic Signal
  Processing   We describe the design of a correlator system for ground and space-based
VLBI. The correlator contains unique signal processing functions: flexible LO
frequency switching for bandwidth synthesis; 1 ms dump intervals, multi-rate
digital signal-processing techniques to allow correlation of signals at
different sample rates; and a digital filter for very high resolution
cross-power spectra. It also includes autocorrelation, tone extraction, pulsar
gating, signal-statistics accumulation.

2
The categories of this paper are: math
35
The categories of this paper are: mtrl-th
30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
21
The categories of this paper are: adap-org
4
The categories of this paper are: cond-mat
7
The categories of this paper are: hep-th
14
The categories of this paper are: math-ph
36
The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
5
The categories of this paper are: gr-qc
8
The categories of this paper are: hep-ex
10
The categories of this paper are: q-bio
13
The categories of this paper are: quant-ph