[ntp:questions] Stick to PPS, even if the prefer server fails

David Mills mills at udel.edu
Sat Mar 28 02:42:08 UTC 2009


John,

I built two of the radios several years ago with a rather expensive hot 
rock timebase good to pars in 10^10. Unlike all of the commmercial 
radios I knmow about that use a hardlimited approach, mine used a 
linear, matched-filter design that was comforatble at well below -10dB 
SNR.  I gave one of the radios and a rock to P-H, but he has a better 
rock and computer interface. The problem is/was that the radio used the 
ISA interface, which of course exists only in museums. Modern designers 
would use a fast ADC and FPGA and own the world.

Dave

John Ackermann N8UR wrote:

> Poul-Henning is doing some really neat stuff with a software defined 
> LORAN receiver, but he's not actually using that one for timekeeping 
> (that I know of).  I didn't know he also had your design running as well.
>
> John
> ----
>
> David Mills said the following on 03/27/2009 08:24 PM:
>
>> Johm,
>>
>> Don't get me going on the Austron 21--. I had one and a 2200, too, 
>> and they cost me more in repeated repari bills than new Spectracom GP 
>> receivers, so I junked them. As for the Coasties, they have 
>> threatened to turn LORSTAs off every few years since 1990. As for 
>> your suspicion that you are the only NTP server synchronized to 
>> LORAN-C, be advised Poul-Henning Kamp has a clone of my receiver 
>> running in Denmark with a Rubidium timebase. Apparently, LORAN-C has 
>> new life in Europe.
>>
>> Dave
>>
>> DaveJohn Ackermann N8UR wrote:
>>
>>> David Mills said the following on 03/27/2009 05:44 PM:
>>>
>>>> To John: I suspect you know that all LORSTA stations run by the 
>>>> Coast Guard include in the weekly announcement series a 
>>>> time-of-coincidence (TOC) second at which the epoch of the second 
>>>> is equal to the epoch of the GRI. My Astron LORAN-C receiver, which 
>>>> was modified by the Coast Guard, flashes a light at the TOC. The 
>>>> TOCs and the intervals between them vary up to several minutes 
>>>> depending on the GRI of the chain. I made provisions for the TOC in 
>>>> the LORAN-C receiver I built some years ago, but never completed 
>>>> the code to exploit them.
>>>
>>>
>>> Hi Dave --
>>>
>>> Yes, the TOC can be used to generate an on-time PPS.  The Austron 
>>> 2100 (sometimes referred to as the "T" model) receiver has that 
>>> capability (the more common 2100F version does not; it is useful 
>>> only for frequency comparisons).
>>>
>>> I drive one of my NTP servers (a modified Soekris SBC running 
>>> nanoBSD) tied to the Austron 2100, and its crystal oscillator is 
>>> locked to an Austron 2010B disciplined oscillator that is driven 
>>> from the LORAN receiver.  I suspect that this may be the only 
>>> LORAN-based NTP system running anywhere today.  It keeps very good 
>>> time; in fact, its noise is comparable to a similar Soekris box that 
>>> gets its PPS and oscillator from a Z3801A GPSDO.
>>>
>>> Of course, the Coast Guard just announced that they plan to turn the 
>>> US LORSTAs off in 2010 as part of budget cuts.  I don't know if that 
>>> is political maneuvering to get a bigger piece of the pie, or a done 
>>> deal.
>>>
>>> John
>>
>>
>>
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