I see from looking at the (still woefully incomplete) data sheet for the MediaTek MT3339 or MT3337 GPS chip used in the QLG1's YIC5 GPS modules that the duty cycle of the PPS pulse is programmable (doesn't say within what limits) - I wonder if the latest batch from YIC are different from the earlier ones?? The negative-going 1PPS pulse is not uncommon in GPS receivers, as I understand it (though I am far from knowledgeable on this subject).
73,
Steve VE3SMA
