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 ------------------------ Sent from my BlackBerry Wireless thingy while I do other things... -----Original Message----- From: Mark Spencer <[email protected]> Sender: [email protected] Date: Thu, 9 Sep 2010 17:36:39 To: Discussion of precise time and frequency measurement<[email protected]> Reply-To: Discussion of precise time and frequency measurement <[email protected]> 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 <[email protected]> To: Discussion of precise time and frequency measurement <[email protected]> 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. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
