friendica (DFRN) - Link to source

Currently working on an ALS162 time receiver. Getting my paws on NF C 90-002 really helped to think of an easier strategy to acquire and sync with the signal.

Turns out this signal is a 40Bd 3-state TCM.

First step, however, is to write a stub that will generate a baseband clone of the signal. For now I'm able to generate a static frame. The scrambler is implemented, and I'm working on the CRC-13.

An oscilloscope trace of the PPS and ALS162 time signal that mimics a frame shown in Henning Maier's slides for his GRCon'23 presentation: "ALS162 Time Signal SDR Receiver for GNU Radio".
An oscilloscope trace of the PPS and ALS162 time signal for a 58th second with a 0-bit in the timecode part, the sync packet and ALS Identifier.
Zoom on the previous trace to show the rising edge of the PPS signal complies with ALS epoch specification in NF C 90-002.

Phil M0OFX reshared this.

in reply to isithran

friendica (DFRN) - Link to source

isithran

Honestly, the choices that were made are quite elegant, imho: out of 9 phase transitions, you can recover up to 4 bits in 4 cases, more than 1 bit for 4 others, and the last, which is the XOR of the 3 previous bits.
This means you can recover erasures in many cases ✨💜✨
Phase path truth table, associated to a phase transition diagram.

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