[time-nuts] LORAN-C demise
magnus at rubidium.dyndns.org
Sun Nov 29 23:14:24 UTC 2009
bg at lysator.liu.se wrote:
> Well, most of this discussion is about GPS backup. The GLONASS system has
> received global coverage (again) for navigation. Timing is less demanding
> if we consider the static and known position case. In some years we will
> have Galileo (Euro) and Compass (China). Perhaps also regional Japanese
> and Indian (global?) systems. These are systemwise independant of GPS.
> Looking at spectral redundancy - we have L2C available on some GPS SVs, L5
> will come. The other coming systems are also multi carrier frequency. One
> could argue that a jammer on the whole of the 1GHz to 2GHz will take all
> services. But such a wide band jammer is very much less efficient than a
> narrowband L1 carrier version.
L1, L2, L3, L4 and L5 jammers is off the shelf. Not particular
efficient, not to speak of L3 and L4 being of no significant use.
Spectral diversity of the signal, system diversity and coding diversity
helps for some of the failure modes, but you have common aspects such as
receivers, antennas and distance to the sats.
> How about using SBAS (WAAS, EGNOS, MSAS) for single satellite timing use?
> That should be possible? The SBAS do provide a ranging signal if running
> in the right mode, and that should be usable for a timing receiver. Having
> a GEO signal, there should be no problem in using a high gain (parabol)
> pointing directly to the GEO. This will steal many dB from the jammer
> power budget.
The GEO orbit is given and the time of the systems is fairly well kept,
at least so that it would suit many, but not all, needs. Parabol or
hexical antennas could be used. Linear array is another possibility,
althought a simplified approach could be used since it could be oriented
towards the target just as a parabol. For fixed locations elaborate
antennas is possible regardless.
> Perhaps the way to redundancy is getting GNSS receivers using multiple
> carrier frequencies and multiple constellations. Even though it is sad
> Loran-C seems to go away soon.
I still wait for L2C receivers to become commonplace enought.
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