On Mon, 16 Jun 2008 23:08:22 +0300, Theseus
wrote:

Hello to the group,

1. I am wondering whether the new gps signals will replace the oldies.
e.x. when the l2c will be operational ready will the classic l2 signal
stop transmitting? In 2015 when the l5 will be active
what's the reason of having the new satellites transmitting old weak
signals? (except of backward compatibility with old receivers)

2. what's the critical number of l2c transmiting satellites for seeing
the first results in high accuracy applications? i think now 6 are
operational.

Theseus

L2C will be a civil signal modulated onto the existing L2 frequency.
P-code will continue on L2. Unless you have a survey-grade receiver
or a military navigation receiver, you are not using L2 currently
anyway.

L5 will provide a third frequency with a code that is less susceptible
to attenuation by foliage (but still very susceptible). It will not
replace L1 or L2. The more signals in space, the better for
navigation and for surveying.

By "high accuracy applications", I presume you mean slightly enhanced
low accuracy (i.e. consumer grade, metre-level). You will need 5-6
L2C satellites broadcasting in your area, which effectively means most
SVs broadcasting on L2C. The increase in accuracy will be marginal
for most users, from 10m to 1 or 2 (because of iono-free options).

Enhancements such as WAAS may allow consumer-grade receivers to get
reliable metre-level accuracy once two or three frequencies become
available. Currently dual-frequency receivers can get
centimetre-level accuracy using Precise Point Positioning methods and
several hours of data.

steve