[time-nuts] Ublox time/freq aiding was Re: Linear voltage regulator hints...
kb8tq at n1k.org
Sun Dec 14 10:10:40 EST 2014
> On Dec 14, 2014, at 9:46 AM, Neil Schroeder <gigneil at gmail.com> wrote:
> 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.
The oscillator in the LEA-6T is not a VCTCXO and it’s got the same notes on it.
> On Sunday, December 14, 2014, Bob Camp <kb8tq at n1k.org> wrote:
>> 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.
>>> On Dec 14, 2014, at 4:26 AM, Simon Marsh <subscriptions at burble.com
>>>>> 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
>>> 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 ?
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