Yo Steven! On Mon, 8 Jun 2020 18:48:02 -0500 Steven Sommars <stevesommars...@gmail.com> wrote:
> Sounds sort of plausible. However if the GPS doesn't have the
> almanac, how can it get a fix?
A GPS never uses the Almanac to compute a fix. A GPS uses the
Ephemeris to compute a fix. Each satellite sends its own
Ephemeris every 30 seconds. The Almanac is a reduced precision
ephemeris only used to decide what sats should be in use.
If you have a receiver that can receive many satellites at once then
the Almanc is not needed at atll. But there are other things int
subframe messages of use.
> If this is a known issue, shouldn't
> the GPS delay sending validity="A" or otherwise signal that the UTC
> offset may be incorrect?
Most do not.
> This should be reproducible, correct?
Yes, depending on the receiver model, very repeatable.
> What kind of reset will cause
> the GPS to lose the almanac information?
Depends on the receiver type, and if/where is stores the current GPS-UTC
offset. Some GPS have no power down storage, some have battery backed
ram (BBR) and some have FLASH.
> Many Rpi boards have
> batteries or supercaps for power backup.
Yup, but if the receiver is powered down long enough, the stored
GPS-UTC offset will become out of data.
RGDS
GARY
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