[time-nuts] Timing Distribution in Mountainous Terrain

Didier Juges didier at cox.net
Fri Sep 10 02:07:31 UTC 2010


We should start seeing used Loran transmitters on ebay pretty soon (!), and it should not be too hard to build a timing receiver using this signal. If you just want timing, one transmitter may be enough to cover the area of interest.

The low frequency Loran signals do go relatively well over hills, but mountains, I am not sure.
 
Now, I do not know if this would provide the needed precision directly, but it might be enough to servo high quality references through a PLL.

Didier

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-----Original Message-----
From: Mark Spencer <mspencer12345 at yahoo.ca>
Sender: time-nuts-bounces at febo.com
Date: Thu, 9 Sep 2010 17:36:39 
To: Discussion of precise time and frequency measurement<time-nuts at febo.com>
Reply-To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain

Some form of low frequency broadcast system might work as a GPS backup.

This paper provides a comparison of Loran C vs GPS for time transfers.   While 
Loran C is history in the US, this might give some indication of what could be 
expected from a low frequency broadcast system.

http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA427851

I suspect buying cesium oscilators is likely to be cheaper than setting up a low 
frequency broadcast system,designing receivers etc.   But there might be a more 
or less off the shelf way to do this ?

Just a random thought.



----- Original Message ----
From: Hal Murray <hmurray at megapathdsl.net>
To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
Sent: Thu, September 9, 2010 2:57:50 PM
Subject: Re: [time-nuts] Timing Distribution in Mountainous Terrain

Neat problem.  Please let us know what you finally do.

> 1e-11 only buys you 3000 seconds of drift before blowing the 30 ns budget.
> Without going to cesium we will most likely need some form of mutually
> visible synchronization. 

How many Cesiums do you need?  What do they cost these days?  (at that volume 
and govt rates)
What's the long term maintenance cost?

Can you afford to design, debug, and qualify something else at that total 
price?


My straw man for an alternative would be to use the transmitter on the 
airplanes as the signal source.  I think that works if you have extra ground 
stations covering at least some regions which will have enough airplanes in 
them to keep the system calibrated.  But maybe you need those extra ground 
stations anyway so that the whole system doesn't fall apart when 
fire/earthquake/tornado/whatever takes out one ground station.  (If so, you 
have to think about what happens if one station does go out.)



-- 
These are my opinions, not necessarily my employer's.  I hate spam.




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