Differences

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--- datatrak:signal [2020/05/31 13:04] – [Overall signal structure] philpem
+++ datatrak:signal [2020/05/31 17:31] – [Nav slots] philpem
@@ Line 29: / Line 29: @@
 ==== Sync and timing ====
-:!: TODO
+:!: This is incomplete.
 The //SYNC// data is transmitted by the chain master and used to allow receivers to synchronise themselves to the transmitted signal.
@@ Line 43: / Line 43: @@
     * It encodes one bit of the 64-bit synchronisation sequence using either two cycles of a 50Hz sinusoid (a '0') or 1.5 cycles of 37.5Hz (a '1').
     * This is the origin of the "Datatrak Minute" in the clock shown by the Mk.II Locator.
+  * **Gaps** --
+    * 10ms unmodulated period to allow frequency switching, or for the trigger and clock to be accurately synchronised against.
   * **Clock** --
-    * This is a phase-modulated signal with a modulation depth of :?:
+    * This is a phase-modulated signal with a modulation depth of :?: (unknown) :?:
-    * Two bits (one //dibit//) are encoded in each clock block, giving a total of 128 bits per cycle.
+    * It is one cycle of a 50Hz sinusoid, with a starting phase of 0, 90, 180 or 270 degrees. This encodes two binary bits per clock cycle.
+    * The clock signal encodes a coarse time reference
-:!: TODO
+    * :?: Encoding of the 128 bits per loop is unknown.
-  * 10ms settling period
-  * 20ms "clock" signal
-    * This is one cycle of 50Hz sinsuoid, starting at a phase of 0, 90, 180, or 270 degrees. This encodes two bits of the "clock" signal.
-    * The exact encoding of the 64*2 = 128 data bits is unknown.
-    * The clock provides a coarse time reference which seems to repeat after 65536*64*1.68 seconds, or around 78.843 days (4054784 seconds).
-    * The time format used by Mk.II is:  AAAAA:BB:CCCC
-      * AAAAA is the clock (0 to 65535).
-      * BB is the Gold Code (0 to 63) -- the bit position in the sync sequence.
-      * CCCC is the "Gold Code offset". This is possibly a value from 0 to 1680 indicating the time within the current cycle slot in milliseconds.
-  * 10ms settling period
   * 65ms transmitter-to-transmitter data
     * This is possibly used to send almanac data, or to send commands between transmitters.
-  * 115ms transmitter-to-AVL-receiver data
+    * Modulation format is unknown.
-    * This is used to send commands to the receivers.
+  * 115ms transmitter-to-Locator data
+    * This is used to send commands to the Locator receivers.
+==== Clock format (as displayed in Mk.II software) ====
+The time format used by Mk.II is:  ''AAAAA:BB:CCCC''
+  * ''AAAAA'' is the clock (0 to 65535). This repeats every $65536 \times 64 \times 1.68 \mathrm{seconds}$ -- or around 79 days.
+  * ''BB'' is the Gold Code (0 to 63). This refers to the current cycle number; the bit position in the Gold Code sync sequence.
+  * ''CCCC'' is the cycle offset or "Gold Code offset". This is a value from 0 to 1679 which indicates the number of milliseconds since the start of the cycle.
 ==== Nav slots ====
-:!: TODO
+:!: This is incomplete
 During the navigation "slots" two signals are transmitted: first one 40Hz higher than the centre frequency, then one 40Hz below it. These frequencies are known as the "+" (higher frequency) and "-" (lower frequency) signals.