PHD DEC graph - is this screaming polar mis-alignment?

[g__day (Matthew)]

Folk,

Looking at the sawtooth pattern of the DEC guiding (see attached) does the red line mean I have a gradually DEC drift (I estimate I'm within an arc minute of the SCP on a permanently mounted rig).

The pixel scale was about 1.5 arc seconds per horizontal line in the graph - with each of the data points being about 5 seconds apart - the graph shows 500 data points, and there's 18 teeth to the saw - with a pitch of about 3 lines - 4.5 arc seconds.

So if I interpret this correctly (a big IF) I see on the downside about 50 arc seconds of drift in about 40 minutes. Can anyone tell me am I reading this graph correctly?

Basically drift RA looks random +/- 1.5 arc seconds, but DEC drift looks sawtooth - meaning improving my polar alignment just a tad will likely improve my tracking even further.

Thanks all,

Matthew


Matthew

[seeker372011 (Narayan)]

in my experience a sawtooth dec like this could be caused by serious imbalance in dec
happens even when polar alignment is good

[Bassnut (Fred)]

Looks to me like misalignment. It appears to be a drift fast and then over compensate cycle.

Or...... its esquisitely balanced, and lots of backlash.

[g__day (Matthew)]

I think I'll check polar alignment - spend a few hours on it this week whilst the full moon is about. If I'm even an arc minute out - that is discernible and correctable!

Then I'll check balance - I think its a bit off - so tuning certainly can't hurt.

Thanks guys!

Matt

[multiweb (Marc)]

Yep - too much backlash and major inbalance in DEC. That looks like my graph when I have a couple before setting up. Or was it the other way round?