[time-nuts] Loran - any good for timekeeping?

Poul-Henning Kamp phk at phk.freebsd.dk
Fri Apr 21 15:19:57 EDT 2006

In message <44491E9F.1060600 at pacific.net>, Brooke Clarke writes:

>Hi Poul:
>What is a "Frame rate cyclic averaging buffer"?  Is this where  you use 
>a GRI generator to trigger sampling the incoming signal?

It is a buffer which can hold one FRI worth of samples into which I
average the received signal.

In other words, for a 1Msps and 9660 GRI, it will be:

	9660 * 10 * 2 = 193200 samples long

>I've found that the quality of LORAN-C for timing depends on how close 
>you are to the transmitter.  When in the 100 mile range the quality is 
>equal to better than GPS, but when it's many hundreds of miles there's a 
>lot of variation. 

Yes, the skywave at night is the killer problem.

>I'm attaching a gif of the spectrum here from 0 to 200 kHz that goes 
>with the web page:

Looks very typical.

Try this:  set a pulse generator to the gri-rate of a nearby LORAN-C
chain.  Connect it to the external sync trigger of your spectrum analysator

Then set it for start=100khz, stop=100khz, bandwidth=10khz and video
averaging (or whatever it's called)

You should be able to see the loran-C pulses quite clearly.


Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

More information about the time-nuts mailing list