Magnus Indeed the almanac seems to be the problem. I can see what it thinks should be in view. Its not been easy to backout if the satelliets are behind or in the future. My time mis-alignment even though the closks correct within 1 second and the same for my location accuracy. I can manually tell it to track a satellite and it does. Though even at that it seems to have issues I speculate as poor signal to noise. So may have to do some digging. Thanks Paul.
On Tue, Nov 10, 2015 at 9:06 PM, Magnus Danielson < [email protected]> wrote: > Paul, > > On 11/10/2015 08:58 PM, paul swed wrote: > >> There is a good discussion about old GPS receivers that have been running. >> Its the NAVSTAR proteus thread. >> Very good details in that thread about some issues. Such as the 1024 week >> rollover and that the receiver should still keep working. Though the date >> and time would be wrong. >> > > I was surprised that it resurfaced, as we have been beating that issue to > quite some depth multiple times here. > > Given that theory I fired up the 2201. This is the unit that had no down >> converter and I home brewed one using another GPS receiver. Put simply it >> all worked. >> >> But its always been a bit magical. Wait for a full moon, jump 3 times >> counter clockwise... >> Never made sense as to why it worked or really controlling it >> consistently. >> (Why even care for this pain in the ....? Because it has a really good >> frequency offset measuring system.) >> Over time its become more difficult to get it to work even though the down >> converter is having no problem acquiring and locking to satellites. >> >> I think and its a theory its because its looking for SVNs but with the >> wrong PRN. (these would be retired SVN/PRN sequences)The trigger was >> looking at the satellite it wanted and realizing the PRN was not accurate >> and the satellite wasn't even up. >> I need to do some more digging but perhaps over time there are fewer and >> fewer correct PRNs that align to the SVN. >> Does this make any sense at all? >> >> There seems to be no way to tell the system that SVN X = PRN Y >> > > Why should there be? In the GPS signal structure, the SVN number has _no_ > bearing on achieving lock. It's all PRN codes, and as SVN numbers increase > with launches, the PRN codes is reassigned. > > What is relevant is the almanac indicating the rough orbit of all 32 PRNs. > As you wake up from a long and deep slumber, any remains of almanac will be > mostly outdated. Once you have locked onto a single bird, it takes you 12.5 > min to recover the full almanac. If you have or don't have a hint of where > you are can lead you off track for some time if you have old data. > Depending on how good the recovery algorithms are, the time to lock can > vary a lot. > > It might be that it just needs to sit there until it locks a bird, and > then acquire channel after channel. > > Some receivers needs a proper reset to get going with good speed. > > The only other fake out approach as a test will be to find a PRN thats up >> and see if that aligns to a SVN. >> Then manually enter that SVN as a search. >> > > No need. > > 73 de Magnus SA0MAD > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
