[time-nuts] The Demise of LORAN (was Re: Reference oscillatoraccuracy)

Poul-Henning Kamp phk at phk.freebsd.dk
Sun Nov 15 23:52:33 UTC 2009


In message <4B00796D.6030300 at rubidium.dyndns.org>, Magnus Danielson writes:
>Robert Atkinson wrote:

>The directional antenna needs to have their directional lobes towards 
>each sat being tracked. If you try put the nulls towards the jammers 
>then you need to have a fair knowledge of where it is.

The phased array antennas does not operate in CW mode.

Once you have sat lock, you can operate the antennas in time-gate
mode, and only sampling each bird in a very narrow time window &
frequency band around the code-sign-change event and doppler
frequency.

That still does not reduce your antenna to a single beam, certainly
not if you only have 7 elements in 2D config, but for any moving
platform, that will make the 'sidelopes' swinging all over the
place, thus attenuating the jammer but not the intended bird.

And yes, this is not simple, but 97W ought to do it.

For a fixed location receiver, Pos-Hold mode is pretty efficient,
in particular if running of a known stable clock.

Poul-Henning

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Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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