[ntp:questions] Re: NMEA driver clk_fault - OK. Thanks

David L. Mills mills at udel.edu
Tue Sep 16 15:42:49 UTC 2003


I take it you are in the NCAR building surrounded by Crayons. You should
know products are available that rebroadcast GPS signals inside a
building from an antenna located outside the building. At least one of
these does GPS and another converts to CDMA for the same purpose.
Frankly, the only thing these products save is the downlead from the
roof, that can be an awkward installation.

In general, folks have found in a rented building the owners have
discovered a revenue stream in rooftop real estate and charge outrageous
rental fees for rooftop antenna farm. I would then sugest the owner
establish and run a NTP service for building occupants.


Frank Hage wrote:
> RE: NMEA driver clk_fault.  Please Help.
> Sorry folks about the shrill tone of my message. I was able to find your kind
> replies today.
> Thanks to Steven, Allen and others, I'm now on the right track.
> The problems started when someone in the control tower moved the antenna
> closer to the window sill.  The Garmin GPS 16 is a magnetic mount 'pod,'
> with an internal antenna. I have them sitting on the window sills, with
> a clear view of the sky through huge windows. I'm testing a duplicate in
> my office, which has a much smaller view of the sky through a window.
> 1. Idiot me thought V = "Valid"  in the GPRMC output.  A=Valid, V=Invalid
> 2. There's a 30-60 sec delay in change of receiver status after moving.
> 3. Clamping it to the side of my filing cabinets that faces the window
>    really helps reception over sitting directly on the aluminum window
>    sill, even though it has a smaller view of the sky.
> In summary, I've learned to:
> 1. Use Kermit (etc) to setup the unit and pick a good antenna spot.
>         # Turn off all output:
>         $PGRMO,,2<cr><lf>
>         # Turn on GPRMC
>         $PGRMO,GPRMC,1<cr><lf>
>         # Turn on PPS
>         $PGRMC,,,,,,,,,,,,2<cr><lf>
>         Watch the output:
>         # GOOD:
>         $GPRMC,171021,A,4002.2677,N,10514.5021,W,000.0,279.8,110903,010.2,E*68
>         # BAD: - Don't be fooled that the time fields are still available.
>         $GPRMC,171102,V,4002.2706,N,10514.4973,W,,,110903,010.2,E*73
> 2. Running 'ntpd -d -d -d' Shows enough output to see if the messages
>    are valid when the daemon requires valid output.
> 3. Use 'ntpq -p'  And look in the 'reach' column to see if the driver
>    is consistently getting a good signal.
> 4. Thank the good folk who produce and support the NTP Software.
> Thanks again.
> --
> Frank Hage  fhage at ucar.edu
> National Center for Atmospheric Research

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