LORAN-C Friend or Foe? Mike Bedford British Cave Research Association Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire

British Cave Research Association - Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire Overview of Presentation LORAN-C is a radio navigation system intended for marine use. It interferes with cave radios e.g. HeyPhone. Despite it making communication difficult, there are some potential benefits for cavers. Here I provide background on LORAN-C and discuss possible caving applications.

British Cave Research Association - Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire Hyperbolic Navigation (1) LORAN-C is a hyperbolic navigation system. Operates by measuring time distance of arrival of signals from a pair of synchronised transmitters.

British Cave Research Association - Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire Hyperbolic Navigation (2) By using two pairs of transmitters a fix can be obtained.

British Cave Research Association - Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire LORAN-C Frequency 100kHz centre frequency 99% of power within kHz… … but high power transmitters … therefore significant signal at 87kHz … hence interference for cave radios Later presentation on a method of preventing Loran-C interference

British Cave Research Association - Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire LORAN-C Chains LORAN-C is organised in “chains” A chain covers a geographical area Chain comprises master station (M)… … plus 2 – 4 slaves (W, X, Y, Z) More than one chain might be detectable So chains are differentiated by their Group Repetition Interval (GRI)

British Cave Research Association - Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire LORAN-C Timing

British Cave Research Association - Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire LORAN-C Pulses

British Cave Research Association - Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire Accuracy Unlike GPS, LORAN-C accuracy depends on receiver location with respect to transmitters Best on baseline between master and slave because LOPs are closer here Absolute accuracy 185 – 463m Repeatable accuracy 18 – 91m eLORAN improves this to 8 – 20m

British Cave Research Association - Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire Underground Performance Accuracy inferior to GPS… … but LORAN-C is available underground But will signal strength by adequate? Actually s/n is the most important factor and less noise underground Patent Application WO claims improved s/n underground

British Cave Research Association - Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire Underground Accuracy Non-uniform geology Sloping surface topology Therefore accuracy possibly degraded

British Cave Research Association - Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire Caving Applications Accuracy not nearly good enough for normal surveying but… … “differential accuracy” may be good enough for “rough and ready” surveying (e.g. new cave on expedition) Repeatable accuracy might be good enough to permit its use for underground route finding (a contentious application)

British Cave Research Association - Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire Future of LORAN-C (1) For years we’ve been expecting LORAN-C to be phased out – good news for cave radio LORAN-C was turned off in North America earlier this year LORAN-C chains in Europe were transferred from US Navy to host nations in 1995 Some have closed (e.g. Mediterranean Sea)

British Cave Research Association - Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire Future of LORAN-C (2) North East Europe chains were managed by NELS NELS agreement terminated in 2005 However, ad hoc arrangement still exists between host nations and most are committed to continuation in the mid term Stations being upgraded to eLORAN

British Cave Research Association - Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire Chayka Chayka was developed by USSR Similar to LORAN-C Same frequency but different pulse shape Russian Chayka chains also remain operational West Russia chain available in Eastern Europe Some Loran-C receivers also use Chayka signals

British Cave Research Association - Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire Former NELS Chains

British Cave Research Association - Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire Former NELS & Chayka Chains

British Cave Research Association - Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire Where Next? LORAN-C receivers are cheap Former US users off-loading for a few dollars Time for some underground experiments?

British Cave Research Association - Cave Technology Symposium th April 2010, Horton-in-Ribblesdale, North Yorkshire Thank you for Listening Any Questions?