At 2:06 PM +0200 9/9/02, Peter Fuks wrote:
>...Why is it that the receiver needs a higher SNR when in a forest?
In a forest the signals from the satellites fade rapidly, so the
receiver must frequently re-acquire them; and, even before the
tracking loop declares a "loss of lock" and enters a re-acquisition
mode, some observations of the signal are failing validity tests.
One such test is of the integrity of the "navigation message," which
is sent in frames 30 seconds long. The reported SNR is a
time-average, and the average must be higher so that the minima
occurring during fading are not too low.
When the sky is clear there is no deep fading, except when the
satellite is very close to the horizon, in which case there is
multipath interference from the ground reflection.
>Especially if the forest contains spruce, it seems.
Yes. That's because spruce trees are denser than most other trees.
-Chuck
-- The NEC-List mailing list <nec-list_at_gweep.ca> http://www.gweep.ca/mailman/listinfo.cgi/nec-listReceived on Mon Sep 09 2002 - 13:21:01 EDT
This archive was generated by hypermail 2.2.0 : Sat Oct 02 2010 - 00:10:42 EDT