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| To: | LF Group <[email protected]> |
|---|---|
| Subject: | LF: NEO-M8T and H-mixer (SDR) |
| From: | Riccardo Zoli <[email protected]> |
| Date: | Thu, 24 Jan 2019 23:51:32 +0100 |
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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 |
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