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Help with interpreting PHD2 log on G11
¿ªÔÆÌåÓýHi! I've recently upgraded my C8 to a C11, and accordingly, things
started becoming problematic after that....? particularly my
guiding. I have an older G11, with OPW on the RA axis. I normally
have 0.6 - 0.8" RMS before, now I struggled a lot to come below
1". Most particularly, there has turned up some new "bumps" in the
RA and in general RA RMS is around 2x DEC RMS, which is not good
for my stars (elongated). So I have been doing polar alingment, adjusting the RA worm and
all. And finally got it all to play nicely, I get a rather smooth
curve when doing unguided gudiing assistant in PHD2 or acquiring
data in PEMPro. The PE is a bit to big (some +/- 7") but that is
not much cause for worries when it is smooth. Frequancy analysis
shows almost nothing execpt for the worm ger at 239 secs. Nice! So I capture a PEC curve and program my mount. And I see an RMS of about 0.5". I am a happy amateur... for a few minutes. Then there are some "bumps" coming on the curve. Now what is this? So, here is my question to you - what might it be that causes this? Attached is a PHD2 log from last night. There are a lot of
sessions because I do variable stars. But session 15 is the one I
am interested in now - the long one. There are a number of big
bumps, but since most are in RA and DEC at the same time, I assume
that is external things, like a wind gust or a bird landing on the
scope. But when I choose a section betwen those bumps and do a frequency analysis, I get a contribution from something that is around 60 secs. This is the one I worry about now. See the attached screenshot from PHD2logviewer frequency analysis window. Anyone got any idea what might cause this frequency? I know of the 76 secs and the 31.9 secs, but this one....?
Any help much appreciated.
Magnus |
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Magnus, One possible source of the problem may be that your eastward weight bias is insufficient and your RA gears may be "floating" in a wind breeze or gust. I personally have found that the best way to establish proper eastward weight bias is to do short live exposures and nudge the OTA with my hand to see if stars move in live view. I have found that arbitrary eastward weight bias (wherein balance just begins to tip eastward) is more often than not inadequate for real world wind conditions.I suggest that you try increasing eastward weight bias to a point where you estimate wind gusts will no longer make your gears float by applying force on the OTA with your hand that you estimate will be sufficient given the sail area of your setup. Pretend that the pressure from your hand is a gust of wind and from there determine how much balance offset actually works. Do this for both RA and DEC. For DEC my weight bias is tail heavy. The motors and gears will have to work a little harder but they can take it. I do not think it is a problem at all. Just make sure that your power source is sufficient. Note that the power source offered at the Losmandy site is 15v 4.3amps. I too have a C11 RASA on a G11 and get similar wild spikes. Increasing eastward wight bias eliminated it. Hope this works for you too. John
On Tuesday, March 2, 2021, 8:35:32 AM GMT+8, Alexander Varakin <avarakin@...> wrote:
Looks like you took this graph with PEC enabled and I don't think you will be seeing the expected frequencies in that case. Can you share the freq analysis without PEC and guiding? |