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From: commgrp@silver.bacs.indiana.edu (BACS Data Communications Group)
Newsgroups: sci.electronics
Subject: Re: LORAN C
Message-ID: <1454@silver.bacs.indiana.edu>
Date: 12 Apr 88 15:36:42 GMT
Sender: commgrp@silver.bacs.indiana.edu
Lines: 50


>I recently purchased a used TI 9900 LORAN-C receiver.  I would like
>to procure the schematics for this beast.  Is anyone out there familiar
>with this receiver??  The thing is not tracking the Loran stations at
>all....even though the receiver output shows the GRI pulses.  A source
>for schematics or advice would be greatly appreciated.
>
>Charlie Thompson
>(512) 892-6161
>Austin, TX

There may be nothing wrong with the receiver.  LORAN-C works poorly or 
not at all in most of Texas because of unsuitable geometry relative to 
transmitting stations, even though signals are strong.  A baseline 
extension (area of ambiguity) of the Southeast Chain runs between 
Dallas and Austin; my car-mounted Micrologic ML-5000 was totally 
unusable (would not track) from just south of Dallas to San Antonio; 
it gave error indications west of Dallas because the repeatable 
accuracy was greater than 1000 feet (due to very obtuse crossing-
angles between lines of position).

No other LORAN chains have sufficient signal strength in Texas. I 
tried the Great Lakes Chain but couldn't get enough signal from 
Minnesota; it might be worthwhile to experiment with cycle-stepping (a 
weak-signal technique).

New  transmitters, due to be operational by 1990, will fill the "mid-
continent gap" and provide primary coverage in Texas.  Existing LORAN 
receivers will require ROM upgrades to use the new stations.  See 
_Aviation Week & Space Technology_ magazine, Sept. 28, 1987 p. 120.

All LORAN-C stations are on the same frequency, 100.000000 kHz, and 
transmit their pulses in a sequence precisely controlled by atomic 
clocks.  Stations are grouped into "chains" which are selected by 
their group repetition interval (GRI).  Three stations of a chain (a 
master and two secondaries) must be received to calculate a unique 
fix, however, only two stations can establish the receiver's position 
somewhere on a hyperbolic line of position.

LORAN-C transmitting stations are impressive!  Output power ranges 
from 400 kW to 1.2 MW.  Antennas are 600 or more feet tall, with many 
long top-hat radials.  Stations are manned by the U.S. Coast Guard, 
and have diesel generators for emergency power.

--

Frank
W9MKV @ WA8YVR
reid@gold.bacs.indiana.edu
BITnet: reid@iubacs