Thank you for looking at the log, really appreciate it.
PDA is "Polar Drift Align" in PHD2. I have been meaning to get into Sharpcap, just haven't done it yet.
Yes, I use pulse guiding.
Any idea what the RA swings were due to?
And I made no conscious decision to disable backlash comp. I think I left most of the settings "as is" when setting up EQMod. Should I switch it on? To be honest, I still don't quite understand the backlash issue.
P.S. - it's quite possible the guide scope moved slightly in the journey here. But I can confirm what the guide scope was looking at was the same as what the main scope was capturing.
Calibration is needed in order to make sure that when PhD2 sees the star move, say, at a 30 degree angle, it knows how much of a pulse to send in DEC or in RA to return it back. To do that, it must calibrate--move the mount in RA, see how the star moves, then move it in DEC and see how the star moves *now*.
It also computes backlash *in DEC only*--when, upon reversing direction, initially a push results in no motion. In a mount with no backlash, a forward pulse of 50ms followed by a back pulse of 50ms would return to the initial spot--but in mounts with backlash it doesn't, requiring extra pushes (say 50ms forward, and 150ms back to end up in the original spot). Once the backlash has been absorbed, motion in the new direction is normal. This happens because the gears are not perfectly meshed.
The reason backlash is computed in DEC only is that in RA adjustments/corrections are made by stopping and resuming motion, *not* by reversing motion. In DEC (where, ideally, with a perfect PA no motion would be needed) you need to move to make corrections.
PhD2's guiding assistant will also compute backlash for you (and advise, if it's excessive, to guide in one direction only--North or South vs Auto). This has nothing to do with EQMod. The one thing to check with EQMod and PhD2 is the guiding *rate*. The guiding rate in EQASCOM must match the guiding rate in PhD2. See this if you haven't already.
The RA swings may simply be due to the wrong calibration--the mount, in effect, was told to make the wrong corrections. Make sure that you have a good calibration and reasonably good polar alignment, also that the guide rates match, and try again. If the RA (as expected) calms down, and you still have DEC issues, enable backlash compensation *or* guide in one direction.