[time-nuts] Loran - any good for timekeeping?
phk at phk.freebsd.dk
Fri Apr 21 15:19:57 EDT 2006
In message <44491E9F.1060600 at pacific.net>, Brooke Clarke writes:
>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
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