[ntp:questions] Sure gps looses all sattelite fixes

unruh unruh at invalid.ca
Fri Feb 24 20:23:00 UTC 2012


On 2012-02-24, Dave Hart <hart at ntp.org> wrote:
> On Fri, Feb 24, 2012 at 18:52, Chris Albertson
><albertson.chris at gmail.com> wrote:
>> On Fri, Feb 24, 2012 at 10:08 AM, unruh <unruh at invalid.ca> wrote:
>> ..
>>> Is it evidence of some outside noise source (jamming?) , microwave tower
>>> emission?
>>
>> You would need to have a second GPS receiver set up to know that.
>> It's a good idea to have two, hopefully different brand receivers.
>
> If the second GPS has a RS-232 connection you could monitor its $GPGSV
> output using ntpd and see how it compares to the Sure unit at a nearby
> location during the same events.
>
> Alternatively, if you use a navigation GPS borrowed from a car which
> has a satellite skyview diagram, the problem may become obvious much
> more quickly.  If you're getting unlucky with all the birds in view
> being blocked by obstructions during these events, the sky map of
> satellite positions should make it obvious.

There are no moveable obstructions up there on the roof. The only thing
I could think of is that there is a sattelite receiver on the roof, but
it is blocked by a row of offices on the roof between the puck and the
sattelite receiver. It could be broadcasting to the sattelite and
increasing the noise at the receiver.(That receiver communicates with the MOST
microsattelite-- a tiny 6" telescope to look at fluctuations in light
from stars to measure the internal structure of the stars). But I do not
believe that they would be broadcasting for 15 hours steadily. that
sattelite is in low earth orbit and would only be visible for minutes at
a time. 

>
> Good luck,
> Dave Hart



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