LF,

I'm testing a useful trick to allow a quadrature generator to mantain a stable and nominal phase using a GPS module NEO/LEA-M8T.

Normally, an IC 74HC74 is used to generate the quadrature LO signals for a H-mixer (typically in a SDR "Softrock style").

Clocking the IC with TP2 signal (f * 4, so 544 kHz to obtain a 136 kHz frequency conversion), there is a 90 deg. step phase ambiguity. Furthermore, with an undesiderate glitch on the reference clock signal, the phase could wrongly rotate.

So: resetting (clear) the two D flip-flops of the 74HC74 on rising edge of the 1PPS pulse, already reference for PC audio-card, we can keep nominal phasing which is restored every second.