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

[David I. Emery]

On Sun, Nov 15, 2009 at 08:22:50PM -0600, Didier Juges wrote:
> I think the problem with the Monterey Bay jammer was that he was jamming the
> DGPS correction signal, not the GPS signal itself. The DGPS correction
> signal is sent over the UHF band. Most marine GPS are DGPS because they need
> the better resolution it provides, particularly to find buoys and channel
> markers in the fog. The DGPS correction signal does not benefit from the
> spread-spectrum modulation and associated jamming resistance of the GPS
> signal itself.

	That is the first I've heard of a UHF DGPS correction transmission
can you provide a frequency and modulation mode ?    Most I know of are
re purposed LF NDBs or similar transmitters in the 200 to 400 KHz or
so range that transmit a PSK'd carrier with the DGPS data at fairly low
speed on it.

	I have heard of cases of wide area GPS outages noted by many
folks with NON DGPS receivers (DGPS receivers  mostly will just indicate
no DGPS available and still show a pretty good position) that were
caused by UHF signals on the L2 frequency... though I am sure there are
incidents of accidental interference to LF or other distribution of
DGPS.


-- 
  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."