[Milsurplus] Re: Loran C

Sun Sep 5 11:26:54 EDT 2004

Hi

Good point about the GEOS stuff. I wonder if any of the early gear is 
showing up in the surplus world yet.

A lot depends on what you are trying to do. If frequency is your 
interest and you already have a good local standard then a lot of 
things seem to work pretty well. This is especially true if a more or 
less equal amount of processing is applied. If UTC time is the interest 
then things are a bit different.

Basically I'm a frequency guy ....

	Take Care!

		Bob Camp
		KB8TQ

On Sep 4, 2004, at 11:34 PM, Brooke Clarke wrote:

> 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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>>>>
>
>
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