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This page describes other positioning systems that have been used by the oceanographic, hydrographic, and Dynamic Positioining (DP) industries up till now. It doesn't cover wide area systems like Decca, Loran/A and Loran/C, and Omega. If you know of a system I have omitted please send me the details and I will add it to the list.


This was an underwater positioning system made by Decca Survey where beacons were deployed to the seabed and then their positions were measured according to accepted survey techniques. The mobile unit(s) interrogated the fixed beacons in turn measuring the round time for getting an response back. The resulting range measurements were used to compute a surface position in X,Y,Z, and provide this to navigating packages. It was used in the 70s and into the 80s, it has since been supplanted by improved but similar equipments from Sonadyne, and from Simrad, to name two.


Also known as RSDN-20, Alpha is a Russian long range Radio Navigation System, which operates in the Very Low Frequency (VLF) band. It is thought to date from the 1950's and there are five known transmitters, located at Novosibirsk (master station), Krasnodar, Khabarovsk, Revda and Seyda. The transmission format is six time slots each 400mS wide and followed by a 200mS gap, making a total cycle duration of 3.6 seconds. Each site radiates a CW carrier in its appointed time slot, on one of the frequencies 11.905 kHz, 12.045, 12.091, 12.649 kHz and 14.881 kHz. Determination of position is by comparing the phase at some common base frequency, however it is obscure how this is derived. The system is still operational at the time of writing and can easily be heard late at night using a VLF receiver of the 'whistler receiver' type with a short whip antenna feeding a very high impedance amplifier. More in depth information about Alpha may be found here, and details of VLF receivers of the type mentioned above here.


Argo was a product of the Cubic Corporation of the USA. It was also known as DM54. It was a positioning system using phase comparison techniques and operating in the 1.6-2.0 MHz band. It offered accuracies of better than 20 metres at the maximum range of 400km. The way in which Argo operates is different to that of Hi-Fix or similar systems; it operates primarily in the range-range mode with up to seven mobile stations being able to use the same shore stations by means of time sharing. There was also a hyperbolic mode that allowed an unlimited number of users to share the system.

An Argo chain would consist of a master station and up to four slave stations. The transmission cycle is two seconds long, and is divided into seven 'sub-cycles', each of which is further divided into 44mS time slots in which a station may radiate a 36mS long RF pulse- except for the first time slot in a sub-cycle, in which the master station transmits a triggering pulse which is 120mS long.

The cycle commenced when the master station radiates a trigger pulse that, because of its length, is uniquely identifiable by all stations. On receipt of the trigger pulse, the first ship-borne (mobile) station would transmit an interrogation pulse in the next time slot. This pulse was received by all of the slave stations, which measured the phase difference between the interrogation pulse and their own synthesised master oscillator. Each of the slaves then replied in turn in one of the four following time slots, with an RF pulse whose phase was adjusted to replicate that of the received phase. The mobile receiver received all of these replies, and computed its postion by comparing the round-trip phase delay to each slave station. Following the next trigger pulse, the next mobile would transmit and so on until all seven will have obtained positions. There then followed a period of silence before the cycle repeated. Note, the position was still only determined to within one ‘lane’.

Lane identification could be used and required a second radio frequency approximately 10% higher than the main. This facility was not continuously active, the mobile operator having to initiate such a lane-check. Transmissions were then made alternately on the prime and on the lane identification frequencies until the control unit had computed the lane error, which was presented to the operator as a number of lanes. There is the possibility that this was made continuous in a late modification.

Argo stations comprised a Range Processing Unit (RPU) and an antenna coupling unit. The arrangement was the same for all stations, except that the mobile required an additional Control and Display Unit. The transmitter output was up to 100 watts. The units were pre-programmed with up to 16 frequency pairs, and no retuning was required over a 200kHz switching bandwidth. The transmitter incorporated SWR monitoring and would reduce the output power to safe levels when working into a poorly matched load. Antennas could be of between 8 and 30 metres length.

One special feature of an Argo transmitter installation was the phase measuring loop antenna attached to the transmitter antenna. This was used to check the phase of a transmitted signal so that it did have the required phase. This was probably the best solution to the problem of variations around the antenna site, e.g. different moisture levels in the soil of a shore site.

Another feature of the system was the ability to integrate with a variety of navigation or processing computer packages due to several flexible interfaces; GPIB/IEE488 parallel, and RS232 serial out, both being provided as standard.

Some Argo chains were deployed around the N. Sea in the mid 80’s.


Artemis is a short range positioning system developed by Christian Huygens Laboratorium (CHL) of the Netherlands and taken in by the Nederlands Survey Apparaturen BV (NeSA). Thus it came into the Racal-Decca sphere in stages. Operating at 9.7-9.8GHz, the system offered exceptional accuracy (0.5m range and 0.1degree azimuth) and a range of up to 30Km. At short ranges out to about 1.5km this related to +/- ? m beyond this the two elements tended to separate so that range accuracy meant one kept a good distance measurement from the FIXed unit but the angular measurement degraded relative to the distance. Its an easy mathematical relationship – the range in metres is multiplied by the sine of 0.1 deg to give an error value.

The Mobile and Fixed installations consisted each of two Units, an Antenna Unit and a Control Unit; MAU, MCDU, FAU, and FCDU respectively.

Readings were of transmission time from the MAU to the FAU and back again, recomputed to metre ranges; and of an angular measurement made at the FIX-ed station relative to a known (surveyed) point. These were then transferred to the Mobile for use there. The transmitters had an output power of 100mW in the high setting and 3mW at low power/short range. These were the CW ratings so as the transmissions were interrupted at the modulation rates effective power was less. Related to a torch bulb one would have barely seen the glimmer!

It was originally designed in Holland for use in the harbours and waterways there and later typically used with the fixed stations installed on oil production platforms and on other fixed sites, and used to provide positioning to either supply vessels and diving tenders for dynamic control of vessel position. Or as a survey package for a specific survey vessel working in the in the immediate area.

As it was a one-to-one package multiple users created problems for the technicians in avoiding mutual interference. These were to a large extent counteracted by extending the number of frequency pairs accessible and by the selective addressing facility.

There have been many well known versions used since the late 70’s, the Mk3 which has provided the basis for these comments, the Mk4, a development with microprocessors and slightly more user-friendly packaging, and the Mk 5 which is still in current production (2015)

The benefits, features, technical specifications and a downloadable pdf brochure are available from the web site of Guidance Marine Limited who currently own the Artemis brand.:


BRAS and RS-10 are similar hyperbolic position fixing systems which continue to be used in the countries of the former Soviet Union. Their transmissions, thought to originate from chains located around the Baltic coast, may be heard on frequencies around 1810 kHz. The BRAS system appears to comprise a master and two slave stations that transmit sequentially, with a cycle time of about 0.9 seconds. Unusually, instead of a continuous-wave (CW) transmission the chain stations are modulated by a series of pulses at 820 Hz repetition rate, so that the transmission sounds like a series of carriers 820Hz apart when tuned on a conventional receiver. RS-10 uses the same transmission format but allows for a master and up to five slave stations. Read my BRAS/RS-10 page by clicking here.

Chayka (ЧАЙКА)

Chayka is the name of a Russian Radio Navigation System (RNS) that is extremely similar to Loran-C, and you should see Loran sites for more information. There is a high degree of compatibility between the systems and the Chayka chains in the North of Russia are usable by Loran-C receivers. The system has been integrated into the Eurofix (QV) system.


Consol was a beacon system operating at around 300kHz that used an array of 3 phased antennas to produce a rotating pattern of dashes and dots. Following the callsign sent in CW, the listener heard a sequence of dashes that gradually merged into a continuous tones, followed by emerging dots. The whole sequence lasted about 40 seconds.

The British Consol system, and its very close German counterpart code named ,Elektra Sonne' were used extensively for marine navigation during WWII. There is an excellent description and historical perspective at Jerry Proc's web site, here. Be sure to check out the pics of the derelict Lugo station here. I have prepared an audio simulation of the last remaining Consol station LEC at Stavanger, Norway which continued in operation until around 1990.

The method of use was to count the dashes to the equisignal zone, then count the dots. A methematical formula gave the bearing off the station. The theoretical accuracy was 0.6 degrees of arc, or 3 miles at 1000 miles.


Datatrak is a medium-area LF automatic vehicle location (AVL) system operating in the UK, Benelux countries, Germany and Austria. It is operated by Securicor Information Systems in the UK and by Siemens-Datatrak in mainland Europe. It was originally developed to fulfil a need for the monitoring of Securicor's own parcel and security vehicles, however it is now marketed to a number of other customers. The system is a conventional hyperbolic positioning system where a number of stations making up a chain transmit in sequence on a common pair of frequencies in the band 130 to 170 kHz. The receiver calculates it's position and communicates this back to the control centre (Swindon in the UK) by means of a UHF radio system that provides similar coverage to the LF network. The system is enhanced by the provision of Event Activated Tracking (EAT) or 'Trak Bak' as Securicor call the product. This allows a stolen vehicle to be tracked and aprehended. Also, the UHF component may monitor various inputs from the vehicle, providing a telemetry function.

There are apparently 14 sites in the UK but their location is unknown. The sequential transmissions are clearly audible at around 145 kHz in the UK, the interesting thing about them is that they 'warble' as if FSK modulated at around 20bps. Using Manchester coding, the transmission would still be usable for positioning as long as the phase were averaged over many symbols.

The system was decommissioned in the UK in November 2011; it continued to operate in Europe until the following year. There are currently (2015) no known systems operating.


DeltaFix was a modification of Racal's Hyperfix positioning system, so that Differential GPS (DGPS) data could be transmitted using the Data time slot in the Hyperfix transmission sequence. See my DeltaFix page.. The system was decommissioned in 2010.

Electronic Position Indicator (EPI)

EPI was developed by the Coast and Geodetic Survey of the US (later to become NOAA) under Clarence Burmister. It was designed to have the best features of both LORAN and SHORAN, and had a typical range of 250 miles. Development started in 1944 and it was first used in 1947 in the gulf of Mexico. It was used on some significant surveys such as in the Bering Sea, and the US West Coast, and remained in use until 1955. A web page shows an EPI shore station mast, and from this it appears that it probably worked at MF frequencies. No further information available.


Eurofix is not a navigation system in its own right. Rather, it is a method whereby Differential GPS (DGPS) corrections are transmitted using existing Loran-C transmitters. See this link for more details. If it is successul in the market, it will extend the life of the North European Loran chains indefinitely.


GEE was a radio navigation system operating in the VHF band. It was developed during WW2 by a team working under R.J. Dippy at the Telecommunications Research Establishment of the British Government. It was put into service as the primary means of navigation over enemy territory by the RAF, and receivers were carried on most bombers. The system operated in hyperbolic mode, the ground transmitters radiating narrow pulses and the receiver measuring the difference in time-of-flight. The receiver presented received pulses on a CRT display, and the user measured the times by aligning 'strobe' pulses with the received pulses on the display and reading off numbers which were transferred to a map overprinted with a hyperbolic lattice. The system remained in use until 1970. More information can be found here.


Hydrotrac is a positioning system developed and manufactured by Odom Offshore Surveys Inc. of the USA. It operated in the MF band over a frequency range of 1.6 to 2 MHz. It was capable of providing an accuracy of down to 2 metres with a maximum range of 250 nautical miles during the day and somewhat less than half this at night.

Hydrotrac has some features in common with Hi-Fix, such as the use of sequential transmission on the same frequency from a master and up to three slaves, and a triggering signal 60Hz below the pattern frequency. The transmission cycle period is 1.0 seconds with two slaves, and 1.3 seconds with three. The system could be operated in either hyperbolic or range-range mode. Master station (and ship station if used in range-range mode) consisted of a master drive unit (MDU), power amplifier (PA) and an antenna coupler unit, while the slave station equipment consisted of a slave drive unit (SDU), power amplifier (PA), and antenna coupler unit. The RF frequencies were generated by a frequency synthesiser which could be set to any 10Hz step in the band 1600-2000 kHz, and the RF power output of the transmitter PA unit was continuously variable up to 150 watts. The antenna coupler unit permitted antennas of from 10m to 45 m height to be tuned, and the PA contained integral SWR metering. The nominal power supply was 24 volts, negative ground.

One significant difference from Hi-Fix was the way in which station timing was derived. In order to eliminate lane loss through loss of synchronisation, the units contained a timing system that was essentially accurate without external triggering; such that timing would remain in synchronisation over a period of several hours. The receiver was designed so that 256 consecutive valid triggers had to be received before the timing system was updated.

MARS-75 (MAPC-75)

A system still in use in Russia. Very little is currently known about this system.


MAXImum RANge was an experimental system tried out in the early 80’s. It worked in the UHF band (like SLYLEDIS) and promised improved ranges etc:

Tests found it to radiate too wide a spectrum for it to be licensed in Europe.


MicroFix was a Racal Survey product. It operated at C-Band microwave frequencies (5 GHz) and was innovative in using pulse stretching, and compression techniques in the TX and RX sections respectively. The pulse train for transmission was fed into a SAW filter and each pulse spread out into a chirrup. In the receiver the spread chirrup was fed though a corresponding circuit that compressed the chirrup back to a sharp pulse for processing in a more normal fashion. This reduced the measured radiated power and improved its resistance to interference.

The basic premise of operation was in measuring the transmission time (out and back) of pulses of radio energy.

The antennae were constructed to radiate a circularly polarised field so that reflected signals were far better suppressed than with linear polarising. Any reflected signal would have the opposite polarising and would be suppressed by up to 30dB. Various different antennae were produced, both omni-directional and sector types.

The stated accuracy of the system was 1 metre and the specified maximum range was 80km over a line-of-sight path. It could also be persuaded to continue working out to 100Km plus. If one lost lock one then had to return to within 79km range.

There was a mast-head unit with an antenna and containing the transmitter-receiver electronics (T/R), and a Control-Measuring Unit (CMU - model 90600). It was built in to the same casing as the 90515 HyperFix receiver but with different front and back panels.

Communication between the T/R and the CMU was by dual RS422 lines and there could be up to 350m (maybe more) of data cable between the two. Voltage drop in the power lines often meant one had to boost the supply to the T/R when such lengths were involved.

A special advantage with these CMUs was that the internal processors could compute a position provided that co-ordinates for the static beacons had been inserted and a working spheroid set up in them. Thus they could directly give out position data to a plotter, or even just a printer, so acting as a stand-alone package.

Several interface types were available, including GPIB parallel, and RS232 serial out.

The only real criticisms that could be made of the CMU was the limited contrast available in the LCD modules and the lack of back-lighting. These were addressed in later versions and as better components became available.


Miniranger is a product of the Motorola Corporation. It went through many development stages as Miniranger I/II/III; it is also known as 'Falcon' or 'Falcon IV'. It operated in the C-Band microwave region at around 5.5 GHz, although an X-band (9.5 GHz) otion was available and often preferred in Europe. The transmitter power is 400 watts. The system works by measuring the 'time of flight' of short (0.3 uS) pulses of radio energy. A fix was obtained by comparing the distance measurement (range) obtained in this way from 2 or more shore stations. Whilst the accuracy obtained is good, as with all microwave systems the disadvantage is that at these frequencies, the radio range obtainable is strictly line of sight. The range may be extended by mounting the shore stations on high ground and/or tall structures, and the ship-borne antenna at the top of the mast. The accuracy of the system is better than 3 metres and the maximum range 37 km.


Pulse/8 was a Decca Survey product, and another name for AccuFix, and it was in use during the 1970's through to the mid/late ‘90's. It operated in the low frequency band, and radiated a pulse transmission very similar to Loran-C. It was a hyperbolic system using time-of-flight techniques, with station identification by means of pulse pattern recognition and PRI timings.

The transmitting equipment was manufactured by Megapulse Inc. and used an unusual technique of magnetic compression. Large value capacitors were charged up and at set times their energy was released into L-C transformer networks in a set manner and through to the antenna matching coil. As far as I know this was the only tuned circuit in the TX. This is a very simple explanation.

The first receiver used in 1976 by the then Decca Survey was produced by Internav and called the S501. This could be set to receive three ranges and to display any two of them at one time.

A heavy beast full of TTL circuits and with an analogue receiving section. And it always came in a double unit.

The next receiver to be deployed was the Mk4, designed in-house in Decca Survey it was smaller and lighter and better, it could display 3 range measurements continuously. And give output data via several parallel ports..

The last widely used receiver was the Mk7, a tiny beast full of microprocessors and it was again a double unit. The unit could track up to 5? Ranges in each of two chains, display these and drive a track plotter. Didn’t make the tea though!

One could use Pulse/8 in a Range–Range mode providing one had an accurate frequency standard connected and associated hardware/software.

The techniques for this were developed for commercial use in the mid 80s and used where only two or three Pulse/8 ranges were available. These techniques also allowed one to bring Loran C ranges into the solution. Loran C wasn’t monitored to the same level of accuracy as Pulse/8 so the calibration procedures compensated for this different level.

Radio Acoustic Ranging

In the early years of the twentieth century, it had been discovered that sound waves propagated for large distances under water, and could be detected by a hydrophone (underwater microphone). This led to underwater bells being placed on wrecks or dangerous shoals to mark them, and the sound of the bell, which was audible for a range or 10 to 15 miles, would warn shipping. By the outbreak of WW1 networks of hundreds of bells existed. The development of directional hydrophones enabled bearings to be taken on the bells, and experiments into positioning by this means were carried out.

The RAR system, developed in 1923, marked the first time that radio was applied to positioning, and it was the first positioning system to be usable in conditions of zero visibility or at night. It required two or more additional vessels, each fitted with a hydrophone and a radio transmitter, to be located in known positions. The survey vessel had a radio receiver. To obtain a fix, the survey vessel detonated an explosive charge underwater. The acoustic waves from the explosion travelled outwards away from the vessel, at a known velocity. When they were detected by the hydrophone on board one of the vessels, a radio signal was transmitted back to the survey vessel. In this way, a position was obtained by measuring the time delay between the explosion and the receipt of the radio signals. This gave a 'range off' of each vessel.


The Raydist NR-S short range positioning system is a product of the Teledyne-Hastings corporation and was introduced in 1954. Operating in the MF and HF bands betwen 1.6 and 4.0 MHz, it can operate in either hyperbolic or range-range modes and has a maximum range of 250 miles by day and 150 miles at night. It has an accuracy of 10 feet in range-range mode. The equipment is portable and transistorised and operates from a 24V DC supply. The mobile unit ('Navigator') contains the reference oscillator for the system. The signal is relayed through the slave stations in the chain, and a positional fix is obtained by phase comparison.

Raydist had in the 80’s an interesting advertisement with a picture of a man in a white overall painting a white cross on the sea surface.


SeaFix was a Decca product that was a version of Hi-Fix with few (if any) apparent differences. There is a document at the National Oceanographic Society of America's web site that contains a reference to Seafix and a some pictures of a ship installation and a shore based chain transmitter here. It also describes some of the other systems mentioned in this page.

Or, you can just read all about it on my own SeaFix page.


SHORAN is a shortening of SHort RAnge Navigation system, after the style of LORAN- but the technical differences were many. SHORAN used frequencies in the VHF spectrum and had many similarities to Gee, a wartime development to help bombers navigate over enemy territory. Unlike Gee, which was a hyperbolic system, it was a range-range system using a transmitter on board the vessel to interrogate two shore stations. The round-trip time of the radio pulses was measured and this gave the distance off. SHORAN was first used in a hydrographical survey in 1945.


SPOT was another package developed for the N. American market perhaps with not quite enough consideration about compatibility with other services. It was a Range-Range system with a base in tight frequency control, using caesium clocks, and in a chirrup technique. The chirrup or transmitted spectrum was quite wide, from 500KHz to 3-5MHz (as far as is known) and was said to be inaudible on any normal AM RX or a narrow band receiver.

It was also said that the TX power was regulated to keep the received signal below the local noise level. Whether this was the noise level local to the TX station or at a distant RX installation was never explained.

This was tried out in European waters but rejected after a season or two after reports of interference to other (military) users.


Syledis (SYstem LEgere pour mesure le DIStance) was a positioning system manufactured by Sercel of France. It operated in the range 420-450 MHZ in the UHF band. And was primarily used in the range-range mode although a hyperbolic mode could be provided. During the 1980's the English Channel and the North Sea were covered by extensive Syledis chains. The system offered good accuracy at distances of up to 100km from the fixed stations on shore and on platforms. Syledis remained active and well utilised until the early/mid 1990's. It was then in use alongside GPS and DGPS based systems in their early days.

The technical basis was a pulsed transmission with a pseudo PRBS code which was processed to give a propagation time measuring method.

A Syledis beacon was installed at Flamborough lighthouse; the antenna was a four-stack dipole attached to the balcony. The system had a reputation for causing interference to radio amateurs using the 430 MHz band; the latter being allocated the band on a secondary basis to positioning systems.


Trisponder was a short-range position fixing system manufactured by Del Norte Technology Inc of USA. It operated at X-band microwave frequencies around 9.5 GHz. By the use of relatively high peak power pulsed transmitters (1000 watts) along with very narrow pulses it gave a range of up to 80 km and could achieve a range accuracy of 3 metres or better under good conditions. The TX included a magnetron with its associated magnetic field and could provide interesting effects when moved by or installed too close to a magnetic compass on a vessel. Far from all ships had gyro compasses in the 60s and 70s!

The system comprised a number of fixed/stationary transponder units and a vessel-mounted transponder (beacon) with a control-interrogator unit (yellow painted Display Measuring Unit –DMU) which interfaced to one or more display units. All units operated from 24 V DC and despite the high peak RF output power, the transmitter-receiver units only consumed an average 17 watts of power.

The principle of operation was that of time-of-flight range measurement, but by means of a time-sharing (CDMA) principle up to 4 mobiles could use the same fixed stations, three mobile users was a more realistic number. Each mobile could display ranges to 2 fixed stations. And four DMU users could operate on the same chain of remote stations.

Trisponder - DMU540

In the early ‘80s an updated control unit was released called the DMU540. A more versatile item it could range to up to 4 different beacons and the results were shown on an orange C.R.T. as a precursor to the LCD screens of MicroFix. It would work with both the older and the slightly updated type of beacons. Another major advance was that the DMU540 had an internal microprocessor and could perform the computations to convert the measured ranges to a geodetic position PROVIDING that correct co-ordinates for the remote stations and geodetic constants had been inserted.

Trisponder 450

In the late 70s-early 80s a UHF variant of Trisponder was tried out, it was possibly a variation on Shoran and Maxiran techniques. It did not come into general use in Europe.

Last Modified 30/11/2015