At 23:48 08 April 2019, Martin Gregorie wrote:
On Mon, 08 Apr 2019 14:33:53 -0700, moshe.braner wrote:

Ah, wasn't saving a bit or two in the data packet worth all this
trouble? :-)

Newer GPS signal formats have lengthened the epoch to 8192 weeks, so the
next rollover for receivers using CNAV messages should be in 157 years
time, though older receivers should work as long as the Legacy messages
continue to be transmitted using 1024 week epochs and the receiver
remembers (or can be told) the epoch number).

I found this stuff he

https://en.wikipedia.org/wiki/GPS_signals

Its quite an interesting read.


Most flight recorders receive transmissions on the L1 frequency which does
not include the epoch. L2 and L5 frequencies do contain epoch information.

L1 GPS Engines (a bought-in compenent) have a Real-Time clock which is
maintained by a rechargable battery which is part of the GPS Engine (not to
be confused with any other battery in the recorder).

IF this battery becomes discharged the epoch number is lost.