[ntp:questions] Sure gps looses all sattelite fixes

unruh unruh at invalid.ca
Sat Feb 25 18:24:38 UTC 2012

On 2012-02-25, David J Taylor <david-taylor at blueyonder.co.uk.invalid> wrote:
> "unruh" <unruh at invalid.ca> wrote in message 
> news:qfS1r.13334$Pc2.3258 at newsfe13.iad...
>> On 2012-02-24, David J Taylor <david-taylor at blueyonder.co.uk.invalid> 
>> wrote:
>>> "unruh" <unruh at invalid.ca> wrote in message
>>> news:cmQ1r.3572$py5.2962 at newsfe09.iad...
>>> []
>>>> The graphs of the signal strengths at the edges of these dropouts is 
>>>> in
>>>> ftp://theory.physics.ubc.ca/outgoing/drop{out,in}.pdf
>>> Could not access this page in Firefox.
>> These pages.
>> dropout.pdf and dropin.pdf sorry if my use of the  bash syntax confused
>> you.
> Thanks.
> []
>> It has. I plotted the location of the satellites in the sky using S/N
>> bands. I can see the whole sky (ie sattelites are tracked across the
>> whole sky-- except for a hole in the northern sky where I guess the
>> satellites never go as viewed from Vancouver.) There are some trees to
>> the east, and they seem to reduce the S/N by about 10dB but they are
>> still visible and tracked even through the trees. (Cedars)
> []
>> Mine are stuck to the iron flashing around the top of the building--
>> about 1/2 a meter wide. But that flashing is not attached to any
>> microwave noisy source AFAIK.
> The correct URLs are:
>   ftp://theory.physics.ubc.ca/outgoing/dropout.pdf
>   ftp://theory.physics.ubc.ca/outgoing/dropin.pdf

Yes, that was what I hoped I was saying. Obviously I was wrong. Sorry.

> You should not be seeing a gap like that.  You could get down to a small 

Agreed. I have now managed to get the GPGSV from a Garmin 18 located
about 5 m away on that same rooftop, and this morning I got a dropout
from the Sure again for about 5 min. while I was also recording the
messages from the Garmin. The garmin shows that during this time, the
weakest sattelites (35-40dB S/N) did show more dropouts, but for brief
times ( a few to about 10 sec) but the stronger (>40dB) showed no change
in their S/N during those times. (When working, The Gamin's minimum useable S/M seems
to be about 35dB, while the Sure goes down to below 20dB and still
tracking Of course when not working the Sure sees nothing)). 

The Sure again completely died over a time span of 3 sec, with all signals (including the 50dB
prior level signals) completely dropping out. It is still dropped out 6
hours later. 

> number of satellites, but not none.  What was the duration of the outage?

The scale is in seconds. The outages have run from about a minute to 17

> I did mean to ask whether the receiver board itself was in a well-screened 

No the receiver board is still just the bare board, located inside the
building. The antenna line goes out the window and up to the roof. The
antenna puck itself is in a  plastic bag magnetically fastened to
the flashing along the top edge of the roof. 

> box, and the whole assembly properly sealed for outdoor operation.  I take 
> it that you have not extended the lead from the antenna puck to the 
> receiver board?

No, I have not extended the lead. I would like to to get more options as to where to
locate the antenna puck, but am not sure what the specs would have to be
for an extention cable. 

I am becoming convinced that either the antenna or the receiver is
defective-- leaning toward the antenna.

> My gut reaction is that if the antenna puck is outdoors you should be OK 

Yes, it is outdoors, on the edge of the roof. of a three story old
building ( Ie, at about 12-14m above ground.) There are two tall cyprus
trees to the east, but looking at the signal strengths, these cost
less than 10dB in the strength of the sattelite signals if the
sattelites are behind the trees for the antenna. 

The Gamin is located about 5 m further onto the top of the roof mounted
on an air fan unit-- I could lead the line from the Garmin through the
roof vents for that fan. And no, I have never seen any evidence of
interference from that fan on the Garmin signals. 
> (unless you were at ground level and blocked by skyscrapers).  I hope you 
> can locate the source of the problem.
> Cheers,
> David 

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