PECPrep

Cliquez ici pour la documentation française


PECPrep is a free, open source application for the analysis of your mount's Periodic Error (PE) and autoguidng performance. It can import data from variety of dfferent capture sources. PECPrep is able to filter wind, seeing effects, linear and non linear drift to isolate the periodic signal associated with a mounts worm drive.  PECPrep can also be used to generate a Periodic Error Correction (PEC) file for use by EQASCOM.
PECPrep can analyse data captured by a variety of popular capture and guiding applications:

Free applications
Commercially available applications
  • K3CCDTools
  • MaxImDl
  • AstroArt
  • CCDSoft
PECPrep also provides template based import that allows the user to specify custom file formats.

PECPRep is available in English, French, Spanish and Dutch and will automatically select the appropriate language based upon your Windows settings. Translation to  other languages is possible, please contact EQMOD@groups.io for details.



PECPrep uses Fast Fourrier Transforms to identify and filter frequency components from the original data. The filter controls can be combined to offer fine control over how the signal is processed and can be used to identify and isolate potential mechanical problems such as excessive play in transfer gears etc.  The PECPrep user interface has been carefully designed to provide the user with clear visual cues whilst data is processed in both the time and frequency domains.
  • Linear regression to remove linear drift
  • Non linear drift effects such as those induced by low frequency oscilations can be removed using a High Pass filter
  • High frequency noise (such as introduced by seeing fluctuations) can be removed using a Low Pass filter
  • Individual frequency components can be removed
  • Individual frequency components can be isolated to assess their contribution to Periodic Error.
  • Auto filter provides a quick inteligent filter selection.




PECPrep allows detailed anaysis of the Frequency Spectrum. Data can be compared against a previously saved reference, perhaps to evaluate the effectiveness of  mechanical adjustments such as bearing replacement/lubrication etc.
  • Different windowing options available for better extraction of frequency/magnitude.
  • Variable frequency resolution allows the tuning of analysis to a particular region of the spectrum.
  • User definable "significant periods" for quick analysis of common mount characteristics.


Once the periodic error signal has been filtered and smoothed the resulting cycles can be combined to build a Correction Curve.
  • Individual cycles can be removed
  • Weighting factors allows control over releative influence of each cycle
  • The residual error display allows the user to determine the best fit Correction Curve.

PEC curves can be further or manipulated via the PEC Curve Arithmetic  tab:
  • Curves can be refined by subtracting error data from a second recording.
  • Automatic synchronisation of data with respect to stepper motor position.
  • Phase to compensate for sytem delays.
  • Resynchronisaton of correction phase via manual alignment.


For further information about PECPrep and VS-PEC see the following:
PECPrep User guide (pdf)
VS-PEC Overview and Workflow (pdf)
PEC & Guiding (pdf)

Download PECPrep

Lastest execuatble, source and documentation available via EQMOD@groups.io.

PECPrep is free. It is not tied to any specific commercial products and there is no hidden agenda behind its development.    We would urge anyone interested in PECPrep to try it out for themselves without prejudice.