Principle of Data Format Conversion

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Principle of Data Format Conversion The data is
recorded at natural speed (4Gsp/sec) in a RAM
and played back to 16 different correlators that
operate at 1/16th the speed (250 Msp/sec). The
16 correlations are performed on consecutive
signal segments and are added together
later. (Thanks to the signal for being
stationary) The RAM is circularly organized so
the segments are better called sectors.
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All Read pointers are synchronous. Delay is given
by Write pointers offset
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Basic sequence Every 4 nsec One block of 16
samples is written at the WP address. The WP
address is incremented by 1 One block of 16
samples is read at one of the 16 RP
addresses. The sector number is increased by
1. The downloaded block is pushed into the
corresponding correlator via a 16-sample
parallel-to-serial converter.
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A few assertions It takes the same time
(16x4nsec) for the correlators to load and
process 16 samples from the P/S converter as for
the Read Pointer to poll the 16 sectors. It
takes the same time for the Write Pointer to
cover the full RAM space as for one Read Pointer
to read one sector.
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The geometrical delay It is the time spent by
one sample in the RAM between its writing and
its processing. For convenience all the Sector 0
players (one per antenna) synchronously start at
RAM address 0 at the beginning of each 32pps
event. The write pointer of each antenna is
offset by the corresponding delay value. One
RAM location represents 16 samples, or 4 nsec of
signal. 12 microseconds (4 kilometres) use 3000
RAM locations.
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Blanking When one Read Pointer reaches the end
of one sector, it jumps back to the beginning.
The correlator shift register is still full
with old samples that would not be correlated
with the new ones. Integration must be blanked
while the correlator pipe gets purged. The
related loss of time is (correlator
length/sector length) e.g. 1k/128k
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Overwriting When the Write Pointer has
completed a full turn, it starts overwriting the
old data. It is important that the data on one
sector should not be overwritten before the full
sector has ended being read. This does not occur
as long as the geometrical delay does not
exceed 1/16th the reading time of one
sector. Next is a timing diagram where all this
can be seen
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Next comes an animation that may facilitate the
understanding. For this the RAM space has been
deployed linearly although its nature is rather
circular. One cursor hit represents 16 cycles
of 4 nanoseconds.
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Sector F
Antenna Y
Antenna X
Delay Y
Write pointer
Delay X
Write pointer
Sector 0
Sector 1
11
Sector F
Antenna Y
Antenna X
Write pointer is 16x faster
Sector 0
Sector 1
12
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
13
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
14
Sector F
Antenna Y
Antenna X
Sector 0
Delay Y
Delay X
Sector 1
15
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
16
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
17
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
18
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
19
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
20
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
21
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
22
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
23
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
24
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
25
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
26
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
27
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
28
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
29
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
30
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
31
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
32
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
33
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
35
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
36
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
37
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
39
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
50
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
52
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Delay Y
Write pointer
Delay X
Write pointer
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
59
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
60
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
61
Sector F
Antenna Y
Antenna X
Sector 0
Delay Y
Delay X
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
64
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
68
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
69
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
70
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
75
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
78
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
79
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
80
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
81
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
82
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
83
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
84
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
85
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
86
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
87
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
88
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
89
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
90
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
91
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
92
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
93
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
94
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
95
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
96
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
97
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
98
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
99
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
100
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
101
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
102
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
103
Sector F
Antenna Y
Antenna X
Sector 0
Sector 1
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That's all Folks !