[Milsurplus] Re: Loran C

[Brooke Clarke]

Hi John:

The radio time transfer systems, in chronological & quality order are:
WWV - H.F. radio, suffers from large path length changes
WWVB - 60 kHz - much better than WWV, but still has a dinural change
LORAN-C - 100 kHz pulse system , much more stable than WWVB
GEOS Satellite - has variable path length that needs corrections, still 
in service
GPS - by knowing the receiver position, the time can be very accurate.  
All the prior systems required user input to determine the propagation 
delay, but with GPS  you get an absolute time referenced signal (need to 
correct for antenna to receiver time delay).  Less than 30 ns from the 
UTC edge.

Have Fun,

Brooke Clarke, N6GCE

-- 
http://www.PRC68.com
http://www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com



J. Forster wrote:

>I agree. I prefer my Austron 2100F to a GPS receiver. My local standard is
>always within a few parts in 10E-12. BTW, I don't like the disciplined
>oscillators by Austron. The jump changes are annoying, IMO. Loran does not seem
>to have the diurnal shifting problems common with the 60 KHz from NIST, but that
>may be a path length / propagation issue.
>
>-John
>
>
>
>Bob Camp wrote:
>
>  
>
>>Hi
>>
>>A lot depends on where you are relative to the Loran transmitter(s) in
>>question. If you have an over the water shot and it's a reasonable
>>distance to the station then you can get some pretty amazing time
>>domain stabilities out of good old Loran-C.
>>
>>The nice thing about Loran-C continuing on is that all sorts of gear is
>>still out there. Most of it is in good enough shape to be quite useful.
>>
>>        Take Care!
>>
>>                Bob Camp
>>                KB8TQ
>>
>>On Sep 4, 2004, at 4:18 PM, Brooke Clarke wrote:
>>
>>    
>>
>>>Hi John:
>>>
>>>The LORAN-C system is a totally redundant system when compared to GPS
>>>and this is part of the requirement needed for WAAS, which is an FAA
>>>program for aircraft blind landing.  It's my understanding this is the
>>>reason that LORAN-C is not being shut down.  Note that classical
>>>LORAN-C receivers (pre DSP chip) only tracked the stations in one
>>>chain (3 or 4 stations), but there is a new LORAN-C receiver that's
>>>DSP based and tracks "all in view" stations.  This is similar to a 12
>>>channel GPS receiver, except that there are about 40 LORAN-C stations
>>>in the US.
>>>
>>>As to the question about which receiver type to get for precision
>>>frequency & time applications, the answer is GPS.  You can get on the
>>>order of +/- 30 ns from a GPS receiver designed for time transfer,
>>>like the Motorola units.  Prior time transfer systems were:  LORAN-C,
>>>WWVB, WWV.  There are a number of disciplined frequency sources on the
>>>market that take in the 1 Pulse Per Second output of a GPS receiver
>>>and use that to remove the drift from a 10.0 MHz oscillator.  Kind of
>>>like automatically adjusting the fine frequency knob on an HP 105
>>>oscillator on a continuous basis.
>>>
>>>73,
>>>
>>>Brooke Clarke, N6GCE
>>>
>>>--
>>>http://www.PRC68.com
>>>http://www.pacificsites.com/~brooke/PRC68COM.shtml
>>>http://www.precisionclock.com
>>>
>>>      
>>>
>>>>Date: Sat, 04 Sep 2004 13:10:45 -0400
>>>>From: "J. Forster" <jfor at quik.com>
>>>>Subject: [Milsurplus] Loran C
>>>>To: Test Equipment List <test-equipment at mailman.qth.net>
>>>>Cc: Milsurplus <milsurplus at mailman.qth.net>
>>>>Message-ID: <4139F714.3BC77E45 at quik.com>
>>>>Content-Type: text/plain; charset=us-ascii
>>>>
>>>>A week or two, someone was asking about the anticipated life of the
>>>>Loran system
>>>>in the context of whether to buy a Loran or a GPS receiver as a
>>>>standard of
>>>>frequency (time interval). While not scholarly, here are a couple of
>>>>articles I
>>>>just came across:
>>>>
>>>>http://www.nutsvolts.com/toc_Pages/aug04toc.htm
>>>>http://www.nutsvolts.com/toc_Pages/sep04toc.htm
>>>>
>>>>Of course, spending $100 million does not mean the system will not be
>>>>shut down
>>>>on October 2nd, but it seems unlikely.  FWIW,
>>>>-John
>>>>
>>>>        
>>>>
>>>m
>>>
>>>
>>>
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>>>
>>>      
>>>