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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