Re: Cloud Cover and GPS reception

mike wrote:
Sam Wormley wrote:
mike wrote:
Sam Wormley wrote:
berniejconnors wrote:
I can't believe that I keep reading the same mis-information about
consumer grade, hand held, GPS receivers. The following is a portion
of the description on the new Magellan Triton 2000 receiver:

================
Triton is designed for precision navigation, offering the fastest GPS
positioning acquisition in the industry with the SiRFstarIIIâ„¢ chipset.
An integrated high-sensitivity antenna provides reliable signal
reception even in heavy ***CLOUD COVER ***, canyons or deep woods.
Built-in signal augmentation reception (WAAS/EGNOS) provides 3-meter
accuracy.
==============

Am I mistaken? I thought *** CLOUD COVER *** had little or no effect
on GPS reception.

Bernie.


As millions of GPS receiver users know... GPS work just find
in rain and snow storms! With a signal wavelength longer than
20 cm, droplets of moisture making up clouds, rain, snowflakes
and hail have little effect on the L-band GPS signals from
space.

The signal loss due to any and all conditions in the troposphere
is no more than 2 dB making it insignificant generally.


L1 and L2 Navigation satellite Signal Power Budget

Parameter L1 P-Code L1 C/A-Code L2 P-Code
-----------------------------------------------------------------------
User minimum received power -163.0 dBw -160.0 dBw -166.0 dBw
Users linear antenna gain 3.0 dB 3.0 dB 3.0 dB
Free-space propagation loss 184.4 dB 184.4 dB 182.3 dB
Total atmospheric loss 2.0 dB 2.0 dB 2.0 dB
Polarization mismatch loss 3.4 dB 3.4 dB 4.4 dB
Required satellite EIRP +23.8 dBw +26.8 dBw +19.7 dBw
Satellite Antenna gain at 14.3° 13.5 dB 13.4 dB 11.5 dB
worst case Block II off-axis angle
Required minimum satellite antenna +10.3 dBw +13.4 dBw +8.2 dBw
input power 10.72W 21.88W 6.61W


I believe the numbers, but do have one bit of experience. Last week, when it was raining cats and dogs with a lot of wind, my gps had adequate signal strength from all the visible satellites, but could not achieve a fix.
Certainly not enough data points to draw
a conclusion, but interesting...maybe dB is not the only parameter of interest??
mike


Trying to come to first fix?
Definition of first?
Problem was it wouldn't fix...period.
Unusable.
Water on any surface between the antenna and signal's from space?
Like I said, heavy downpour, high wind.
Wet foliage?
Like I said, heavy downpour, high wind.
Roof is still wet, but it works fine now.

Also like I said, the measured signal strength for the satellites
was within normal range. Don't think it was a dB problem.
Maybe more like a reflection (phase) problem.
Like I said, maybe dB is not the only parameter of interest.
mike







All it takes is a quarter inch of rain on a roof to kill the signals.
It goes without saying that GPS receivers are not designed to operate
inside building or vehicle without external antennae.
.

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