Re: LF: NEO-M8T and H-mixer (SDR)

[Markus Vester <markusvester@aol.com>]

Hi Ric,

Good idea! You can check the effect on my grabber: I've injected an auxiliary carrier into the right channel of the topmost speclab instance, so the colour on your frequency indicates phase instead of azimuth. If you like you could temporarily interrupt the carrier and verify that it comes back with same phase.

Autodecoders are looking out for you and Joe, like last night.

Best 73,
Markus

 


-----Ursprüngliche Mitteilung-----
Von: Riccardo Zoli <riccardozoli80@gmail.com>
An: LF Group <rsgb_lf_group@blacksheep.org>
Verschickt: Do, 24. Jan. 2019 23:56
Betreff: LF: NEO-M8T and H-mixer (SDR)

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.

All the best

73 de Riccardo IW4DXW