AW: [time-nuts] 1pps signal presence with no GPS signal.
df6jb at ulrich-bangert.de
Thu Jul 7 11:03:02 EDT 2005
whether turning off the 1pps with no gps reception is a good idea or not
depends completely on the electronics that actually uses the 1pps for
steering. If (and only if) it is intelligent enough to identify this
condition as being a indication for no reception and falls to holdover,
then it is a good idea. Because Motorola could not know in advance what
tricky things you would put behind their receiver they cannot be blamed
for not making it a default!
If you want to play a save game, never (i.e. NEVER) use the 1pps alone.
Always check the serial TRAIM messages for validity of the 1pps. Once
you hooked up anything that can understand the receiver's serial
messages, you should seriusly question yourself if you do not want to
use the sawtooth correction value in the steering loop. Most GPDO
designs seem not to use the sawtooth correction value despite of its
> -----Ursprüngliche Nachricht-----
> Von: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von David Kirkby
> Gesendet: Donnerstag, 7. Juli 2005 15:07
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] 1pps signal presence with no GPS signal.
> Javier wrote:
> > Hello,
> > The 1pps signal on a M12+ is switchable. It can be selected
> to be on
> > all
> > time or on only when tracking at least one satellite.
> > Regards,
> > Javier, EA1CRB
> Is turning off the 1pps, the best thing to do if controlling
> a crystal
> or rubidium? It seems most logical to me, so I can't
> understand why the
> default is to not to.
> David Kirkby
> > David Kirkby wrote:
> >> I have a Synergy GPS unit, which is fitted with a Motorola M12+
> >> receiver. Even if there is no signal (even no antenna
> connected) the
> >> 1pps light flashes on the front and there is a 1pps signal at the
> >> output connector.
> >> It would seem to me that if you lock a crystal/rubidium or
> >> to
> >> a GPS system, the last thing you want to do is to steer
> your source
> >> from a 1pps signal that must be pretty inaccurate. I
> assume this gets
> >> derived from the uncompensated crystal oscillator on the Motorola
> >> board, and so is far less accurate than the source you are phase
> >> locking to it.
> >> I would have thought it more sensible to cease the 1pps signal as
> >> soon
> >> as a GPS is not locked to at least one satellite.
> >> Comments?
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> David Kirkby,
> Please check out http://www.g8wrb.org/
> of if you live in Essex http://www.southminster-branch-line.org.uk/
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