LORAN-C Friend or Foe? Mike Bedford

LORAN-CFriend or Foe?

Mike Bedford

British Cave Research AssociationCave Technology Symposium 2010

17th April 2010, Horton-in-Ribblesdale, North Yorkshire

British Cave Research Association - Cave Technology Symposium 201017th April 2010, Horton-in-Ribblesdale, North Yorkshire

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.


Hyperbolic Navigation (1)

• LORAN-C is a hyperbolicnavigation system.

• Operates by measuringtime distance of arrivalof signals from a pair ofsynchronised transmitters.

Transm itter 1

LO Ps

ExtendedBaseline

Transm itter 2


Hyperbolic Navigation (2)

• By using two pairsof transmitters afix can be obtained.

Tx 3

Tx 1 Tx 2

Am bigu ity


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 preventing

Loran-C interference


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)


LORAN-C Timing

M X Y Z M

~200 S1m S 2m S

G R I

ED (X)

ED (Y)

ED (Z)


LORAN-C Pulses

0

T i m i n g s f r o m 3 r d z e r o - c r o s s i n g ( 3 0 S )

50 100 150 200


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


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


Underground Accuracy

• Non-uniform geology• Sloping surface topology

• Therefore accuracy possibly degraded

FromM

FromM

FromZ

FromZ


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)


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)


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


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


Former NELS ChainsTransmitter Designation

Emission Delay (µS) Location Country

Coordinates Power (kW) Latitude Longitude

Lessay 6731 Chain

M Lessay France 49°08′55.224″N 01°30′17.029″W 250

X 13,000 Soustons France 43°44′23.099″N 01°22′49.584″W 250

Y 27,300 Anthorn UK 54°54′41.949″N 03°16′42.587″W 250

Z 42,100 Sylt Germany 54°48′29.975″N 08°17′36.856″E 250

Bø 7001 Chain

M Bø Norway 68°38′06.216″N 14°27′47.350″E 400

X 14,100 Jan Mayen Norway 70°54′51.478″N 08°43′56.525″W 250

Y 29,100 Berlevåg Norway 70°50′43.014″N 29°12′15.980″E 250

Eiði 9007 Chain

M Eiði Faroe 62°17′59.837″N 07°04′26.079″W 400

W 14,200 Jan Mayen Norway 70°54′51.478″N 08°43′56.525″W 250

X 28,000 Bø Norway 68°38′06.216″N 14°27′47.350″E 400

Y 41,100 Værlandet Norway 61°17′49.435″N 04°41′46.618″E 250

Sylt 7499 Chain

M Sylt Germany 54°48′29.975″N 08°17′36.856″E 250

X 14,100 Lessay France 49°08′55.224″N 01°30′17.029″W 250

Y 29,500 Værlandet Norway 68°38′06.216″N 14°27′47.350″E 250


Former NELS & Chayka Chains

Rugby

Jan Mayen

Lessay

Soustons

Berlevåg

Sim feropol

SlonimKarachev

Petrozavodsk

Bø

Væ rlandetEi ið

Sylt


Where Next?

• LORAN-C receivers are cheap• Former US users off-loading for a few dollars

• Time for some underground experiments?


Thank you for ListeningAny Questions?

LORAN-C Friend or Foe? Mike Bedford

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