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windytan / redsea

Command-line FM-RDS decoder with JSON output.
MIT License
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Clock recovery #14

Closed windytan closed 8 years ago

windytan commented 8 years ago

Redsea should recover the clock signal and integrate over the DPSK bit-time to ensure best SNR. Currently there is no locking whatsoever and the signal will fade in and out at the difference frequency between TX and RX clocks.

Suggested fix: PLL

This locking could be implemented as a PLL. There is a PLL readily available in liquid-dsp.

Caveat

How to present an estimate of the phase error to the PLL in the presence of gradual 180-degree phase shifts?

Suggested fix: symsync

There's also a symbol synchronizer in liquid that probably does everything needed for carrier & clock recovery

Caveat

How to use it in binary DPSK? The example for QPSK does not work for RDS.

windytan commented 8 years ago

Fixed the issue using liquid's DPSK receiver at twice the RDS symbol rate.