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Why GPS Satellite Visibility?



I want to thank those who answered me on this subject, I had figured I would
get more observations on this one. I will explain a bit more for you. First
just
in case that some of you are wondering why I brought this here, I called the
commercial side and got NO or worse yet, a really bad reply, so I figured I
would bring it to the amateur community where I believe I will get a good
reply.

The problem is this; a customer I work with is putting in a switch for a
iDEN
system, (the same hardware Nextel uses, which is of course produced by
Motorola) one of the requirements is that the distance be no more than 100
feet from the antenna to where the timing data goes into the switch, it is a
TIMING limitation not a cable loss issue (I have run GPS sigs well over 100
ft down good old Belding 9913 with no problems using a amplified antenna
of course) I had originally recommended that the antenna be placed on the
roof of the building, but this would place the switch too far from the
antenna,
so a possible solution is to place the antenna on a parapet which is about
100 ft down the side of the building and would put the antenna about 20 ft
from the side of the building. This would be no problem were it not that the
building is located in Manhattan, and there are tall buildings all around
it.
The actual sky view is much reduced due to the buildings. Prior to going
forward with this location we need to make sure that the GPS can see at
least 1 satellite all of the time. Remember this not for position
determination
it is only for timing and as per Motorola the GPS time base receiver only
needs to see one satellite in order to provide proper timing, but it must
always
see a satellite. What I need to know is how long do I need to capture the
visible satellite count (I have the software to do that) before the orbits
start
to repeat? from experience I know that 24 hours is too short a time because
of prior work with GPS, but I do not really know HOW long I need to capture
before I start getting a repeat of previously captured data. This is all I
need to
know, how long do I captured the VISIBLE satellite count before it starts to
repeat? This is NOT the above the horizon count this is the actual number of
satellites (along with the signal level)  that the receiver can see. What I
will
do with the data is graph it and we should be able to see if we have a
period
when no birds are visible as a 0 count. (I can also search for a 0 count in
the
data but a graph is prettier than a 0 count search.... B-] )

Tnx again folks, I did get good replies but I think my question was not as
clear as it should of been, and as I expected I did get much better replies
than
those obtained by making a phone call to the manufacturers.



Chuck Hast
Telecomms Consultant, Utility Partners.
WEB			www.utilpart.com
Office number:		813.282.8828 x 1175
C-phone number:		813.765.6743
E-mail:			wchast@utilpart.com
SMS  < 150 characters:	8137656743@mobile.att.net

ARS			KP4DJT

To paraphrase my flight instructor;
"the only dumb question is the one you DID NOT ask resulting in my going out
and
having to identify your bits and pieces in the midst of torn and twisted
metal."



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