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1 INTRODUCTION

In the second half of the twentieth century, both in

maritime and air navigation, ground-based

radionavigation systems were widely used, most

often based on the measurement of the phase

difference of signals received simultaneously from

different transmitters, and thus classified as

hyperbolic systems. The popularity of the phase

difference technique, especially in the first half of the

20th century, can be explained by the imperfections of

the time patterns, which could not ensure sufficiently

accurate synchronization of independent radio wave

sources at broadcasting stations, sometimes even

hundreds of kilometres away. Therefore, the solution

was to adopt the principle that one of the system

transmitting stations is the master station, controlling

the emission of signals from subordinate (slave)

stations. In simple terms, it can be assumed that in fact

the transmitters of the subordinate stations

retransmitted the signal of the main station.

This variant of the radionavigation system has

been reproduced in different variants differing in the

frequencies used, the power of the transmitters and,

certainly, some details with respect to the method of

forming the signals. Therefore, in different areas there

were different systems with a larger or smaller

operating range, differing in accuracy and, above all,

requiring different receiving devices from the user.

The Loran C and DECCA systems were the most

widely used, but there were many systems of local

interest and scope. It is significant that these systems

occurred mainly in the northern hemisphere, in the

southern hemisphere only elements of the DECCA

system were distributed in small numbers (on the

southern tip of Africa and in a few places in

Australia).

The Russian ALFA System in the Context of the

Development of Radionavigation in the 21st Century

A. Felski

Polish Naval Academy, Gdynia, Poland

ABSTRACT. For nearly the entire post-World War II period, naval and air navigation relied primarily on

ground-based radionavigation systems. However, the spontaneous development of satellite systems gradually

led to their disappearance. They are currently used partly in air operations and marginally in maritime

navigation in some areas around Asia, in Russia and in the Middle East.

However, at the beginning of the 21st century, the threat of effective interference with satellite systems began to

be raised, which led to an increased interest in restoring or upgrading ground-based systems as backup systems

in the Western world. In this context, the approach of Russia is interesting, as it is associated with the vast

majority of deliberate GPS interference. There are reports in the world literature that various ground-based

radionavigation systems operating in Russia are still observed. The article analyses, on the basis of the few

available sources, information on the ALFA system, about which the least is known, and there are many

indications that it is ready for use.

http://www.transnav.eu

the International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 15

Number 4

December 2021

DOI: 10.12716/1001.15.04.01

724

Against this background, a special place is

occupied by the Omega system which, with a small

number of transmitters, thanks to the use of very long

waves (30000m, i.e. about 10kHz) ensured global

coverage. Work on the system was started by the US

Navy in the late 1950s [8], but it was not until 1971

that the system became operational. In the meantime,

the US Navy lost interest in the system, because the

first TRANSIT satellite system, which was also created

at that time, turned out to be much more perfect, so

the Coast Guard was made responsible for OMEGA

[5]. However, the turbulently developing satellite

systems of the time gave it too much competition,

especially in terms of accuracy. TRANSIT provided an

accuracy of 150m while OMEGA position accuracy

ranged from 2 to 4 Mm, obviously due to the

difficulty of taking into account the phase variation of

very long waves on the propagation route. This

eventually led to the abandonment of OMEGA and

the shutdown at the end of September 1997.

The development of satellite systems also led to a

gradual reduction in the use of other systems using

ground-based transmitters in favour of satellite

techniques, and in fact by the end of the 20th century

almost all these systems had been withdrawn from

use. Only a few elements of the Loran C system

remained on the Asian coast of the Pacific Ocean and

in Saudi Arabia and its Russian counterpart (copy) -

Chaika [2], [7].

However, the monopoly of satellite navigation

systems came into question at the beginning of the

21st century in the face of abundant evidence of

effective jamming and spoofing of GPS receivers.

Similar risks for other GNSS systems are currently not

reported, but this may be due to the incomparably

smaller number of users of these systems compared to

GPS. In this situation, discussions have resumed on

the need to ensure the availability of other sources of

navigational information so as to ensure that

navigation is also possible when GNSS is not

available. The solution may be a radionavigation

system based on radio signals with completely

different characteristics. However, conditions in space

limit the use of other radio wave bands, so there has

been a resurgence of interest in ground-based

systems.

Therefore, there was a growing interest in

proposals to upgrade the existing infrastructure,

especially the legacy of the Loran C system. In this

respect, at the end of the 1990s, the idea of Eurofix

emerged, which was implemented in Saudi Arabia at

the beginning of the 21th century by upgrading the

pre-existing Loran C infrastructure. A competing

proposal has also emerged, known as e-Loran. The

prevailing opinion was that the modernization of the

remaining Loran C stations (especially the use of

existing, huge antenna installations) gives the

opportunity to create a system with completely

different signal characteristics, of which the following

are particularly valuable: low frequency of 100kHz in

comparison to about 1.5 GHz of satellite systems, and

large transmitter powers, measured in tens and

sometimes hundreds of kW. It was assumed that these

features greatly reduce the possibility of interference,

although the limited range of such a system remains a

disadvantage. However, the ranges of such a system

can be estimated at 1,000 nautical miles, making it

reasonable to assume that, apart from the open

oceans, where deliberate GNSS interference seems

unlikely, other areas can be protected from hostile

activities. This issue is beyond the scope of this article,

so we will limit ourselves to stating that this research

is currently being tested in the USA, Great Britain and

South Korea [6], [14]. Research is also underway,

initiated by IALA, to modify DGPS and AIS systems

so that additional signals synchronised to the world

time scale (R-Mode variant) can be transmitted

through them, providing the basis for their use for

positioning purposes [15]. In this situation, the

question arises about Russia's attitude in this context

2 RUSSIAN GROUND-BASED

RADIONAVIGATION SYSTEMS

Russia, back in the days of the USSR, but also

afterwards, was going in the same direction as the

world, especially the USA. Shortly after the first

satellite system (Transit) was launched in the USA, the

Cicada system, a very similar satellite Doppler-type

system. Only a few years behind GPS, the USSR

started to implement the Glonass system, which is a

very similar solution. It was similar before with

regard to radionavigation systems deployed on Earth.

The best known example of this is the Chaika system,

which is so similar to the Loran C system that in the

1990s there was even an agreement to cooperate,

resulting in the establishment of joint chains in

northern Europe and the Far East [6]. This cooperation

was abandoned after a few years with the decision to

exclude the first American stations. However, while

all USA-administered stations have not been

operating since spring 2010, the Czajka system is still

working.

Against this background, the Russian counterpart

to the OMEGA system, which was abandoned in the

US as recently as the 1990s, is intriguing, while there

is evidence that its Russian counterpart, according to

official documents, underwent an upgrade in 2000

and was operational at least as late as 2017 [9]. An

explanation for this may be related to the fact that

Russia is identified as one of the countries that is

linked to a large proportion of cases of various GPS

jamming [13]. A party which willingly and effectively

uses methods to jam satellite navigation systems

should expect similar capabilities from others, so it is

worth protecting itself and maintaining backup

systems.

Already in the fifties in the USSR, as well as in the

USA, work began on a very long-range

radionavigation system, which, according to many

authors, was caused by the need to ensure navigation

of nuclear submarines. However, there are also views

expressed, for example [5], that it was more important

on the American side to provide navigation for long-

range bomber aircraft (B52). Information on such

topics has always been scarcely available. Although in

the 1990s the Russian side changed their approach

and started to provide some information, especially

on the Glonass system, and the closer cooperation

then established in the context of Loran and Chayka

also resulted in many details being provided on this

725

system. However information on the Russian

equivalent of OMEGA has always been extremely

scarce.

Nevertheless, the website of the Russian Institute

of Radionavigation and Time (RIRT) in Saint

Petersburg was available on the Internet (recently

archived), which provided some information that may

be considered official [9], since they show, inter alia,

that this institution was responsible for building this

system. The system is also of interest to enthusiasts,

among whom Trond Jacobsen has published

particularly accurate information via the Internet [3].

Less detailed, but a valuable supplement to this

information is provided by Alan Cordwell [7] and

Jerry Proc [5]. Out of the book publications, the works

[2] and [1] can be useful, in which basic technical

information about the system is published.

Information on the existence of the ALFA system was

also confirmed by representatives of Russia at several

international conferences.

This system is known in Western literature as

ALFA (an early version of it also functions in

literature as SIGMA), and in Russian publications it is

code-named RSDN-20 (the abbreviation comes from

the name Radionavigacionnaya Sistema Dalniej

Navigacji, which can be translated as a long-range

radio navigation system). It is clearly modelled on the

OMEGA system, especially the frequencies emitted by

the system are similar (very long waves of the 10-15

KHz range) and the sequential principle of signal

emission. However, there are also significant

differences from the American counterpart.

According to the information available on the web

portal (RIRT) [9], the system had been under

development since the mid-1950s but was only put

into operation in 1972 (an astonishing coincidence

with the available knowledge of the American

counterpart) although some Western sources cite 1968

as the year the system went into operation with a set

of three stations: Novosibirsk, Khabarovsk and

Krasnodar (SIGMA version). According to [2], in 1991

the configuration was supplemented with two

additional stations: Seydi and Revda. In the same year

(in August), such information was also presented by

the chairman of the Soviet delegation at the meeting

of the International Omega Association in Vancouver,

General Anatoly Funtikov, who also informed that the

new transmitters operate on a new, previously not

used in the system, frequency 12.090773 kHz. Official

statements justified this by making the system

available to civilian users.

Table 1. Transmitters of ALFA system and theirs

localisation.

_______________________________________________

Simbol Name Latitude Longitude

_______________________________________________

NS Nowosybirsk 55

45’22”N 084

26’52”E

KD Krasnodar 45

24’18”N 038

09’29”E

CH Chabarowsk 50

04’24”N 136

36’24”E

MR Revda 68

02’08”N 034

41’00”E

SE Seydi 39

28’16”N 062

43’07”E

_______________________________________________

Source: [3], [9].

The institute considered to be the creator of the

system states that the accuracy of determining the

position was then estimated at 2 to 7 km. There it is

stated that the range of the system is 10,000 km from

the main station, which is located near Novosibirsk.

This value should be treated with scepticism, because

in 2000 the aforementioned Jacobsen recorded the

system signals [3] in Halden (approx. 90 km from the

SE from Oslo) and clearly states that the signals from

Seydi and Khabarovsk stations have not been

registered. This second station in particular is relevant

in this context, as several sources, including the

manufacturer of the RIRT system state that this station

was operating at the time, and is closer than 10 000km

(approx. 7 000km) from Halden. Moreover, the same

materials contain information that in 2000 the

modernization of all five stations of the system was

completed, providing a positioning accuracy of 1.2 to

1.5 km over more than 70% of the Earth surface! This

seems unlikely, if only because the system's

transmitters were deployed exclusively on the

territory of the former USSR. At the same time,

however, it is worth noting that the creators of the

system declared the power of transmitters as high as

500kW (compared to 10kW in the OMEGA system).

At the turn of the 20th and 21st centuries, the

system consisted of five stations, one of which served

as the main station, and the others - as subordinate

stations. This is an important difference to the

OMEGA system, where all stations functioned

independently and the user could freely compose

pairs of stations to determine the distance difference.

It is worth noting that the names used in the table are

not unique. None of the stations are located in any of

the above-mentioned towns, and the Khabarovsk

station is also referred to in some sources as

Komsomolsk-on-Amur. The point is that the emission

of such strong signals at such low frequencies requires

a large antenna field placed outside human

settlements. In fact, Khabarovsk station is located 28

km from the village of Elban, which in turn is 60 km

from Komsomolsk-on-Amur and 200 km from

Khabarovsk. The city of Novosibirsk is located

approximately 150 km from the antenna field

associated with the station under this name, the Revda

station is approximately 120 km from Murmansk, and

the Krasnodar station is located 26 km from

Poltavskaya and 70 km from Krasnodar. In turn, the

Seydi station is about 140 km from Bukhara, so it is

located outside of Russia, currently in Turkmenistan.

They all have a distinctive shape that can be

identified in the images available on Google Earth

because they are a set of seven masts arranged in a

regular hexagon, at the tops of which stand the

aforementioned masts, with the seventh placed in the

centre of the area.

Figure 1. The antenna field of Novosibirsk. Source: Google

Earth.

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The very low frequencies used in the system

would suggest that the transmitting antennas should

be very high, but there is no official data on this. On

the Internet, however, there is a photo of the antenna

system near Novosibirsk, which shows 7 partially

overlapping masts, giving an idea of their size. The

area in the picture is partly covered with forest and

gives an idea of the size of the antennas. Furthermore,

since all the antenna fields are similar in shape and

the antennas are about 600m apart, it can be inferred

from the photograph that the antennas are at least

300m high. This is consistent with information on the

OMEGA antenna system, which operated at similar

frequencies [5] and had antenna masts over 300m

high.

Figure 2. Novosibirsk antennas (foto: Dmitry Afonin ©

28.06.2009) accessible at: [12]).

The above-mentioned RIRT website [9] also states

that the system was upgraded in 2000, but also states

that the Seydi station was shut down in January 2010

without giving reasons. This may be justified by the

fact that it is currently located on the territory of

Turkmenistan, so unlike the others - outside the

territory of Russia. Oddly enough, the same source

also reports that the Revda (Murmansk) station has

been switched off, which is more difficult to explain.

This state of affairs is confirmed by Cordwell stating

that in 2017 only Novosibirsk, Krasnodar and

Khabarovsk stations were operational. The fact that

the system was operational in October 2016 is also

evidenced by the information available on the

YouTube channel

(https://www.youtube.com/watch?v=GnLLC0G_3Mo),

video recording of the spectrum analyser with audio

evidence of the reception of the three stations. If the

system were to operate as a hyperbolic system in the

configuration of Novosibirsk and two subordinate

stations, one would expect a zone of operation similar

in shape to the version shown in the Fig. 3.

Figure 3. The probable operating-zone of the system in the

configuration KD-NS-CH. Source:author.

It is likely that the reason for the abandonment of

the Murmansk station was due to financial or

geopolitical aspects (need for navigational services in

other areas?). However, it is not impossible that in

view of the development of atomic time standards

(RIRT is the producer of time standards for the

Glonass system), similar stable standards were

implemented on the three transmitters of the old

system and it was upgraded to the rang variant (R-

mode). It is also possible that Revda station is treated

as a backup for special situations, because its activity

is still periodically monitored.

Analysis of the probable zones of the system

operation suggests that originally the developers were

interested in Arctic waters, there are suggestions that

the zone of operation even includes Alaska. It can be

seen, moreover, that this largely refers to the Pacific

Ocean, including the seas surrounding the coasts of

China, Korea and Japan (including their territories)

and the Baltic Sea, which seems natural for Russia's

armed forces. However, it may be surprising that the

Black Sea was not within the operating zone of the

system. Perhaps it was recognised that poor positional

accuracy did not make the system attractive in this

area . The analysis of the older version of the system

also suggests that the station in Turkmenistan was

probably set up in an earlier configuration to ensure

the availability of the system in the eastern part of

the Mediterranean Sea. In turn, the configuration

noticed in 2016 and 2017 seems to suggest the

intention to provide signals in the waters of the Indian

Ocean and the Red Sea (which was probably not

sufficiently guaranteed before), regardless of the

range still maintained in the waters of the Far North

and the seas surrounding the coasts of China, Korea

and Japan.

3 SYSTEM ORGANIZATION

Jacobsen reports that the system started working in

1962, which was confirmed by Harvard researchers

who registered such signals and reached operational

status in 1968 in a constellation of three stations

(SIGMA version). This configuration was finally

returned in the 21st century, despite the

modernization declared in 2000. In the same year 1968

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these stations were reported to the International

Frequency List declaring the following frequencies:

− F1 = 11,905 kHz;

− F2 = 12,500 kHz;

− F3 = 12.649 kHz;

− F4 = 13.281 kHz;

− F5 = 14.881 kHz;

− F6 = 15.625 kHz.

Originally, the system worked on the F1, F3 and F5

frequencies. Later, after launching two additional

stations, the frequencies F2, F4 also became active, but

additionally a previously undeclared frequency of

12.700kHz appeared. In this combination, the

frequency F6 (15.625 kHz) seems to be of particular

importance and is noticed extremely often by system

observers, but it is not impossible that it is not part of

the system but a transmission coming from the same

source for other purposes. It is possible that these low

frequencies are also used for communication,

especially with submarines.

The organization of the system operation is very

similar to that used in the OMEGA system

(previously, a similar solution was proposed by

DECCA in the DELRAC system, which was not finally

implemented). Individual transmitters emit a

sequence of signals consisting of six identical elements

(slots) lasting 400ms each with 200ms intervals in a

3.6s cycle. It is a combination of signals from different

stations on different frequencies. It is worth noting

here that OMEGA worked with segments of various

lengths, and the entire cycle lasted 10 seconds.

Recordings of these signals are available, inter alia,

via the Internet [10] and [11]. Spectrogram of system

signals received on May 14, 2000 in position 59o

08'12”N and 011o 23'55”E, at 0656UTC is shown in

Fig. 4 [3].

Figure 4. Spectrogram of system signals received in Norway

on May 14, 2000. Source: [3].

On the above spectrogram, signals from the

Novosibirsk, Krasnodar and Revda stations can be

identified. There are also presented in Tab. 3. No

signals are received from Khabarovsk, possibly

because of the distance, but also no signals are

received from Seydi, a station which is at a similar

distance from southern Norway as Novosibirsk.

There have undoubtedly been changes in the

organisation of the system and it is difficult to state

clearly what the current state of affairs is. The

registrations made by Jacobsen show that in 2000 the

system operated on frequencies (in kHz) 11.905,

12.649 and 14.881 and these registrations show the

activity of stations in Novosibirsk, Krasnoyarsk and

Revda. Cordwell lists additional frequencies 12.045,

12.091. The latter referred to the shutdown stations

Revda and Seydi.

The issue of organizing emissions into cycles is

also not very clear. While in the Omega system the

transmit cycle was 10 s the basic cycle in Alpha was

assumed to be 3.6 s. However, it is known that in the

OMEGA system the phase of the radio wave

generated in each slot was constant and consistent

with the start of the slot. It was observed in the

Russian system that the phase of the individual pulses

is not the same in each of the 3.6 second cycles and is

repeated every 7 cycles (7 x 3.6 = 25.2 s). Moreover, the

signals emitted by the transmitters are not ordinary

continuous wave (CW), but the pulses also contain

unknown modulation, which may mean conveying

additional information, regardless of the likely use of

the phase for navigation measurements. Information

on signal modulation suggests that this is the effect of

modernizations made at the turn of the century, and

therefore would suggest some newer solutions. It is

possible that these solutions are similar to what is

implemented as part of the modernization of the

Loran system to the e-Loran version. Modulation

could, for example, be used to communicate

corrections to users similar to that used in DGPS

systems and thus guarantee better accuracy.

The OMEGA system used perfect atomic time

standards at each of the eight stations, which did not

require mutual synchronisation. In the ALFA system,

regular phase jumps are observed at all stations. This

takes place at 0000 Moscow time (2100UTC) with the

same value and can be interpreted as a

synchronization of all transmitters. This is also due to

the fact that the individual emission cycles on the

individual frequencies do not change by a full phase

within 24 hours, so these jumps are also intended to

reset the phase at the beginning of each day. These are

360o divided by 7 which meant jump of 51.4o for the

frequency 11.905kHz, 2x360o/7 = 102.9o for 12.649

kHz and 3x360o/7 = 154.3o for the frequency of

14.881kHz. Jacobsen also points out that all the

frequencies in the system are the result of duplicating

the common base frequency Fo = 744.047619047619 Hz

(744 and 1/21Hz). The exception is the frequency he

calls F3p which differs from F3 = 14881.09127 by 5/36

Hz and is only transmitted from the main station.

Table 2. The cycle of the transmission by stations of ALPHA system after the modernization in 2000.

__________________________________________________________________________________________________

1 2 3 4 5 6

__________________________________________________________________________________________________

Nowosybirsk 11,904761 12,648809 14,880952 14,881091

Krasnodar 14,880952 11,904761 12,648809

Chabarowsk 14,880952 12,648809 11,904761

Revda 12,648809 12,090773 14,881091 11,904761 14,880952

Seydi 11,904761 12,044270 14,881091 14,880952 12,648809

__________________________________________________________________________________________________

Source: on basis of [3].

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Table 3. The interpretation of recordings from the spectrogram (Fig. 4).

__________________________________________________________________________________________________

1 2 3 4 5 6

__________________________________________________________________________________________________

14,881091 Novosibirsk

14,880952 Krasnodar Nowosibirsk Revda

12,648809 Revda Nowosibirsk Krasnodar

12,090773 Revda

11,904761 Novosibirsk Krasnodar Revda

__________________________________________________________________________________________________

Source: author.

The frequencies of the oldest stations in the system:

− F1 11904.76190 Hz = 16 x Fo

− F2 12648.80952 Hz = 17 x Fo

− F3 14880.95238 Hz = 20 x Fo

The frequencies of the additional (Revda i Seydi):

− F4 12090.77381 Hz = (260/16) x Fo

− F5 12044.27083 Hz = (259/16) x Fo

In addition, extremely rarely emitted signals are

observed at other frequencies. This may mean that in

the system, due to its military purpose, there is a

backup variant of operation, sometimes activated to

check its efficiency.

4 CONCLUSIONS

While the development of satellite navigation systems

in the Western world has led to an almost complete

abandonment of land-based systems, and only in the

last decade have there been tendencies to restore the

possibility of using ground-based systems as a

backup, such solutions have never been completely

abandoned in Russia. The incidental reports available

from unclassified sources show that at least some of

these systems are in a usable state, as evidenced by

reports of receiving signals from these systems.

It is worth recalling that Russia inherited from the

USSR the very long-range ALFA system, the long-

range Chaika (Loran C) system and the closer range

systems: BRAS and MARS. A few years ago, a

message appeared on the Internet that the Mars

system was observed in the Black Sea, the Chaika

system is still functioning, while the ALFA system

remains the most mysterious. According to the

information discussed in this article, which is

available through non-confidential written sources,

both on paper and electronically, it can be concluded

that even if this system is not used on a daily basis, it

has undergone an upgrade in the 21st century and is

most likely in a state of fitness for use as a backup

navigation system, in case satellite systems, primarily

the Glonass system, are blocked.

REFERENCES

[1] Forssell B. Radionavigation Systems. Artech House.

Norwood 2008.

[2] Groves P.D. Principles of GNSS, Inertial, and

Multisensor Integrated Navigation Systems. Artech

House, Norwood 2008.

[3] Jacobsen T. The Russian VLF NAVAID System, ALPHA,

RSDN-20. Dostępne na: trond.jacobsen@halden.net

(02.11.2020)

[4] Loran-C User Handbook. Commandant Publication

P16562.5. United States Coast Guard ran-C User

Handbook 1980.

[5] Proc J. Omega. Dostępne na

http://www.jproc.ca/hyperbolic/omega.html

(10.11.2020).

[6] https://www.ndgps.go.kr/html/en/gnsys/gnsys_040101.h

tml (11.11.2020).

[7] http://www.radionavigation.alancordwell.co.uk/systems.

html (22.05.2020).

[8] https://www.skybrary.aero/index.php/Omega

(11.11.2020).

[9] https://web.archive.org/web/20080613063718/http://ww

w.rirt.ru/onas/rirt-e.htm (12.06.2020).

[10] https://www.youtube.com/watch?v=g0VbDIkX6gU

(14.11.2020).

[11] https://www.youtube.com/watch?v=Ys9Qmm4-ws4

(14.11.2020).

[12] http://www.panoramio.com/photo/23892185

(08.11.2020).

[13] https://navcen.uscg.gov/?Do=GPSReportStatus# 26-07-

2020

[14] Ward N., Hargreaves C., Williams P., Bransby M. Can

eLoran Deliver Resilient PNT? Proceedings of The

Institute of Navigation 2015 Pacific PNT Meeting,

Honolulu, Hawaii, April 20–23, 2015, pp. 1051–1054

[15] Wirsing M., Dammann A., Raulefs R. Investigating R-

Mode Signals for the VDE System. Oceans 2019

MTS/IEEE Seattle Conference doi:

10.23919/OCEANS40490.2019.8962635.