I did not see my correction for the missing URL posted on the list, so will
repost it now. Sorry if this results in a repeat message in your mailbox.

Go to this web site and download the original QST article for a GPS based
frequency standard (originally published in QST, July 1998). The software in the
PIC has filtering to stop glitches upsetting the VCO which is locked on to the
satellite. This sounds like the sort of filtering software you are after. You
may be able to get him to supply you with the source code, which you may well be
able to cut and paste into your application.

This time I will try putting the web address in
http://www.rt66.com/~shera/