what is a 66 channel gps receiver for and why do we need 66 channels while there are only 24 satellites?

Question

what is a 66 channel gps receiver for and why do we need 66 channels while there are only 24 satellites?

Answer 1

There are 66 possible GPS channels. The new receivers can monitor all 66 simultaneously, so when a sat comes into view, the receiver can lock on almost instantly. Older receivers had to scan through the channels, so they could be slower to lock on.

Answer 2

Mainly marketing, bigger numbers sell better.



There are actually 30+ satellites up right now, in theory at certain times 12 of them could be in sight at the same time. Plus depending on exactly where you are there may be up to 3 WAAS satellites in view.



So you could maybe use 15 channels for a few minutes a day if you were in just the right location.



There are two legitimate reasons why you could use more than 15 channels:

1) Better time to first fix. Unless you know where you are and what's overhead you need to search for the satellites, for a number of reasons that search is very complex and the more channels you can throw at it the faster you will be able to find some satellites, get a location and narrow down the search.

2) Multiple bands/systems. Some high end GPS systems (typically a thousand dollars or more) can also use the L2 and L5 signals from GPS or the russian GLONASS system. More things to track means more channels.





So for consumer systems, 66 channels means a few seconds faster to give you that first position fix and a nice big number for the marketing people to put on the box.



Assuming you don't need a position the instant you switch the thing on and you're only using the basic GPS signals then in the real world there is very little point in more than about 12 channels.

Answer 3

Satellites trasmit digital spread spectrum.



66 channels means it can listen to 66 channels at once, and figure things in software. There is also the WAAS transmissions.