Re: Re: New APP for satellite observing

From: Carlos Bella (carlos.apodman@gmail.com)
Date: Tue Sep 03 2013 - 12:25:40 UTC

  • Next message: alberto rango: "Pierre Neirinck."

    Instaled and testing, thanks by the initiative Coberllini
    
    Regards
    Carlos Bella
    **
    
    
    2013/9/3 satrack@libero.it <satrack@libero.it>
    
    > Hi George,
    >
    > many thanks for your test and suggestions. In the next release I will show
    > more
    > details on the correction factor. I will also improve its determination as
    > suggested.
    > (Initially, the program was programmed to use the top 1 synch, but it was
    > not
    > useful during tests when I wanted to see the result of each synch).
    >
    > The shown Tacc is equal to the round trip time (RTT) divided by 2. The time
    > error is computed as the difference between the time of the request +RTT/2
    > and
    > the server time. Therefore, in your example it would be indeed 1.8 s.
    >
    > The mean Tacc from my location is of about 80 ms. Unfortunately, one of the
    > main
    > problems with mobile phones is the network latency. I partially solved this
    > problem
    > engaging the network with a short data transfer during which I perform
    > the time synchronization. Without this trick the situation would be even
    > worse,
    > with RTTs even larger than 0.5 s.
    >
    > I introduced the item "exit" in the menu since I decided to capture the
    > "back"
    > key
    > as input for the stopwatch. This menu item should terminate the
    > application.
    >
    > It would be interesting if someone could test the time deviation with
    > respect
    > to
    > a reference clock.
    >
    > Regards,
    > Simone
    >
    > >
    > >Very Nice!
    > >
    > >1) I love the way I can press up volume, down volume, or back button and
    > get
    > >3 different time indicators so later I know which one was which.  One can
    > >use this to help remember which event is which - for example press the vol
    > >up button when the sat is closest to a known and planned-for bright star
    > and
    > >the vol down button when the sat is closest to an unknown fainter star.
    > >2) I love that I can jump into timing an event, then later sync up several
    > >times until I get a higher accuracy.  Each time I sync all the times
    > adjust
    > >slightly to the latest syncing.
    > >3) Unfortunately the highest accuracy I was able to get with about 30
    > >attempts was "Tacc < 90ms".  This is according to the program (not tested
    > >against something more accurate).
    > >4) It would be nice to display the correction factor you are using.  The
    > >correction factor for my phone was about 1 second.
    > >5) It would be nice to be able to take an average of the top 3 sync events
    > >or the top 1 sync event and not update the times displayed unless the
    > latest
    > >sync event had a "Tacc" better than any previous ones.
    > >6) I assume Tacc is the same as the round trip network time.  Do you use
    > >this information in the syncing?  In other words if the phone says it is
    > 1.0
    > >seconds after the hour and the NTP server says it is 3.0 seconds after the
    > >hour and the round trip delay was 0.4 seconds, do you use a correction
    > >factor of 2.0 seconds or a correction factor of 1.8 seconds? (this assumes
    > >the .4 sec delay was equal on both paths or .2 seconds each way).
    > >7) The "exit application" doesn't seem to work but I'm not sure what its
    > >purpose is anyway.  I would just get rid of it.
    > >
    > >- George Roberts
    > >http://gr5.org
    > >
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    > >
    >
    >
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