At 08:33 AM 5/30/2008, you wrote: >Early GPS receivers used a 10.23 MHz time base. >Probably related to 2^10-1.
yep.. the chip rate for the C/A code is 1.023 Megachips/second, the P code is 10.23 Megachips/second, and the L1 frequency (1575.42) is exactly 154 times the 10.23 MHz, the L2 is 120 times. So you can see that having a 10.23 MHz oscillator is a handy thing in a GPS receiver, especially if you can discipline it with the received signal. These days, one might choose a reference oscillator somewhat higher, so that when you do your 1bit A/D of the signal, you get many samples/chip, and so that the signal directly aliases to somewhere convenient. A lot of receivers use a sampling clock such that you get 1 bit I and Q samples at a convenient sample rate. 4*10.23 would work nicely, eh? 40.92 MHz >Some GPS manufacturers approached HP about making >a 10811 on 10.23 MHz. There is a circuit modification >for 10.23 MHz and some crystals were made (I >have some somewhere). However, I don't believe >any 10.23 MHz 10811's were sold. This unit was >probably intended to meet the need not filled by HP. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
