Hi, I've been working on a SMPTE/LTC project on and off for around a year. But I recently started looking into equipping myself with a more accurate time reference to help me evaluate/calibrate my LTC units. It looks like a GPSDO might be the way to go, and after some forum discussions I 'fell into' another project based around the same tech as my SMPTE one.... introducing "pico-irig", as entertainment really. I am (ab)using the GPIO, rather than using external DAC. Keeping implementation as cheap/simple as possible. I have some demo code running and (to my eye) the output looks workable... I am, however, not an IRIG decoder. https://github.com/mungewell/pico-irig/blob/main/docs/pics/sample_with_lpf.png (the audio samples are also up on GitHub) So the questions: 1). I understand the 1:3 to 1:6 ratio on the ASK levels, but is there a spec on the spectral 'cleanness'? 2). Pico is producing 3V pk-pk with DC offset. In the recorded sample I am AC coupling, is this needed? In general can equipment handle a small DC offset? At present the output circuit is fly-wired mess, I'll probably spin a small PCB with some decent ground/supply. If 'clean' is needed, I can add some filtering on-board, but I'm concerned that this might add some phase shifting to the wanted signal. Cheers, Simon.