[time-nuts] Ublox time/freq aiding was Re: Linear voltage regulator hints...

[Neil Schroeder]

The oscillator in he m8f is a vctcxo and can be steered with feedback or
controlled by the host.

Also the m8f can send compliant DAC words to a TLV8515 and and MCP part via
i2c for external
VCXOs. It accepts their return signal on what would normally  be its
feedback in ports.

On Sunday, December 14, 2014, Bob Camp <kb8tq at n1k.org> wrote:

> Hi
>
> There is also a little note down in the (many) notes section:
>
> Not all features are available with all firmware versions.
>
> It applies to all of the external inputs (like USB and SPI).
>
> Since the oscillator in the uBlox is a TCXO and not a VCTCXO, the aiding
> feature would not help in the case of biasing the unit with a hot air gun.
> It would still loose lock as the TCXO went nuts.
>
> The ideal outcome would be a system that reported against the external
> input rather than the internal TCXO. Since they digitize the external pin
> with the TCXO, the outcome is pretty coarse (10’s of ns). That’s not going
> to help us much.
>
> Bob
>
> > On Dec 14, 2014, at 4:26 AM, Simon Marsh <subscriptions at burble.com
> <javascript:;>> wrote:
> >
> >
> > On 14/12/2014 04:08, dan at irtelemetrics.com <javascript:;> wrote:
> >> > Note that most high-end GNSS timing receivers go one better and
> simply have an external input for the clock. That way you feed your own lab
> clock into the receiver. If you have Rb/Cs/maser you would use that as the
> reference. It's what the national timing labs do, along with dual-frequency
> and post-processing and all the other tricks of the trade.
> >
> >> I think it would be agreat idea also. It's a wonder that more of the
> 'timing' receivers don't have that external clock option! I wonder what
> these Ublox parts use for a clock? Is it something frequency compatible
> with a 10Mhz source??? (Hmm, can we pry one apart to figure it out! ;) )
> >
> > Ublox modules have a 48mhz internal clock.
> >
> > There is the following interesting paragraph in at least the 7 & 8 data
> sheets:
> >
> > ---
> >
> > 1.8.2 Aiding
> > The EXTINT pin can be used to supply time or frequency aiding data to
> the receiver.
> >
> > For time aiding, hardware time synchronization can be achieved by
> connecting an accurate time pulse to the EXTINT pin.
> >
> > Frequency aiding can be implemented by connecting a periodic rectangular
> signal with a frequency up to 500 kHz and arbitrary duty cycle (low/high
> phase duration must not be shorter than 50 ns) to the EXTINT pin. Provide
> the applied frequency value to the receiver using UBX messages.
> >
> > ---
> >
> > I haven't been able to find any information about what this actually
> does though. Anyone know ?
> >
> > Cheers
> >
> >
> > Simon
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