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LORAN-C Friend or Foe? Mike Bedford

LORAN-C Friend or Foe? Mike Bedford. British Cave Research Association Cave Technology Symposium 2010 17 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.

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LORAN-C Friend or Foe? Mike Bedford

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  1. LORAN-CFriend or Foe?Mike Bedford British Cave Research AssociationCave Technology Symposium 201017th April 2010, Horton-in-Ribblesdale, North Yorkshire

  2. Overview of Presentation • LORAN-C is a radio navigation systemintended 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.

  3. Hyperbolic Navigation (1) • LORAN-C is a hyperbolicnavigation system. • Operates by measuringtime distance of arrivalof signals from a pair ofsynchronised transmitters.

  4. Hyperbolic Navigation (2) • By using two pairsof transmitters afix can be obtained.

  5. LORAN-C Frequency • 100kHz centre frequency • 99% of power within 90-110kHz… • … but high power transmitters • … therefore significant signal at 87kHz • … hence interference for cave radios • Later presentation on a method of preventingLoran-C interference

  6. 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)

  7. LORAN-C Timing

  8. LORAN-C Pulses

  9. 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

  10. 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 20061130223 claims improved s/n underground

  11. Underground Accuracy • Non-uniform geology • Sloping surface topology • Therefore accuracy possibly degraded

  12. 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)

  13. 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)

  14. Future of LORAN-C (2) • North East Europe chainswere 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

  15. 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 useChayka signals

  16. Former NELS Chains

  17. Former NELS & Chayka Chains

  18. Where Next? • LORAN-C receivers are cheap • Former US users off-loading for a few dollars • Time for some underground experiments?

  19. Thank you for ListeningAny Questions?

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