THE
RUSSIAN VLF NAVAID SYSTEM,
ALPHA,
RSDN-20
By
Trond JACOBSEN, Halden (NORWAY)
I think nearly everyone interested
in the really low radio frequencies, at one time or another, has heard
the “ bee-boo” sound of the Russian radio navigation system Alpha.
Or more precisely RSDN-20, as the official Russian acronym for the system
is, meaning “ normal long-range navigation system “ where
D stands for long-range. Alpha / RSDN-20 is a hyperbolic navaid, the Russian
equivalent to the now closed western OMEGA VLF navaid system. Although
the former Soviet, now CIS, Alpha / RSDN-20 VLF navigation system has operated
in relative obscurity over the past tree decades, there is little information
to be found on the web, but it has been studied by several individuals,
and it's existence has been publicized at a number of conferences during
that period.
 |
The ALPHA / RSDN-20 radio navigation system is transmitting a 3.6 sec long repeating sequence consisting of six 400 ms long frequency combinations with a 200 ms spacing. The Alpha / RSDN-20 signal spectrogram above are made with GRAM 5.0 and received at my QTH at 59°8’12’’N 11°23’55’’E on the 14 Th. of May 2000 at 0656 UTC. |
Tree of the Alpha / RSDN-20
stations are received, Krasnodar, Revda and Novosibirsk. The far east station
at Khabarovsk and the station at Seyda in Turkmenistan are out of range
or QRT.
The original concept for Alpha
/ RSDN-20 was born in 1957. In 1962 was the start for the implementation
of the navigational system and already then was the signals received and
monitored at Harvard for a few days. “The quality of the signals was poor”
and “the exact frequencies varied like those from rather poor crystals
“, one of the monitoring crew recalls. In 1968 was the system operational
with 3 stations at Krasnodar, Novosibirsk and Komsomolsk-na-Amur. The RSDN-20
transmitter at Novosibirsk was ( and still is ) the master station.
These tree original transmitters are sometimes called Sigma in literature.
The same year was the stations listed in the International Frequency List
with six frequencies; 11.905 kHz, 12.500 kHz, 12.649 kHz, 13.281 kHz, 14.881
kHz and 15.625 kHz. The International Frequency List also reported 500
kW of power to the antenna at each location and at each frequency.
When representatives from Racal Marine Electronics
( formerly Decca Navigator Company ) was attending a fishing exhibition
in Leningrad 1968, they recall visiting a Russian fishing wessel were they
was shown a navaid receiver intended for us in the Arctic waters north
of the former Soviet Union. The receiver was designated by the acronym
PIRS-1R and the navaid system was at that time officially called RSVT-1.
With the tree original RSDN-20
transmitters located almost on a line from west to east across the Russian
continent, the system coverage was obviously not intended for Soviet domestic
use. One would assume it was originally intended for submarine as well
as aviation use in Polar and North American regions and possibly also for
the southern Asia and Indian Ocean regions.
With the prior tree station
configuration of RSDN-20, if one station were off air, the remaining two
would be virtually useless for navigation and the overall system availability
is very limited. In August 1991 a Soviet delegation at the IOA, ( International
Omega Association ), meeting in Vancouver headed by general Anatoliy G.
Funtikov announced that two new Alpha / RSDN-20 transmitter sites had been
constructed, one on the Kola peninsula near Murmansk in Russia and one
near Chardzhou in Turkmenistan. The Murmansk transmitter located near the
village of Revda was given an exclusive frequency F4, 12.090773 kHz. The
same was done in Turkmenistan with the new transmitter at the village of
Seyda ( Seidi in Russian ) near Chardzou. With two more transmitter sites
the navigational system would be more reliable and also more adapted for
civilian use within the former Soviet union. With this inclusion of two
new transmitters followed also a new transmitter sequence. At the same
IOA 16 meeting was there also given information of a new unique frequency,
F3p, from the master station at Novosibirsk. This new frequency was 1/7.2
Hz higher in frequency than the nominal F3. This has also been the observed
with the transmission from Revda and reported but not observed with the
segment 4 transmission from Seyda in Turkmenistan.
The RSDN-20 transmission sequence
The basic signal epoch consists
of six pulse periods in 3.6 sec. Compared to the longer sequence ( 10 sec
) that was used for the Omega navaid, Alpha / RSDN-20 are more suitable
for faster moving vehicles, i.e. airplanes.
The phase of each pulse does
not start at the same value each 3.6 sec epoch but rather repeats in an
overall period of 7 x 3.6 = 25.2 sec.
The pulse durations are 400
msec with 200 msec between pulses. The pulses contain no known modulated
or otherwise information. When the system is off air for maintenance or
other reasons there are sometimes periods with test transmissions with
other phase and sequence patters then the normal one.
OLD RSDN-20
transmission sequence by frequency:
|
Segment
nr. station
Frequency kHz |
1
|
2
|
3
|
4
|
5
|
6
|
| F3 14.880952 kHz |
Novosibirsk
|
Novosibirsk
|
|
|
Krasnodar
|
Komsomolsk-na-Amur
|
| F2 12.648809 kHz |
Komsomolsk-na-Amur
|
Krasnodar
|
|
|
|
Novosibirsk
|
| F1 11.904761 kHz |
Krasnodar
|
Komsomolsk-na-Amur
|
Novosibirsk
|
Novosibirsk
|
Novosibirsk
|
|
 |
A different Alpha / RSDN-20
transmitter sequence. This Alpha / RSDN-20 transmission from Krasnodar
was received at my QTH on the 9.th of May 200 at 0656 UTC. It consists
of a different pulse length sequence then the original one and also making
use of a pulsed signal at the 15.625 kHz alternative frequency. Transmitter
patters like this are not uncommon in periods when the system are off-air
for maintenance.
|
There has been some speculations
that the Alpha / RSDN-20 system use these sequences for special
navigational purposes, until that is confirmed, such speculations are most
likely based on misunderstanding of the basic principles of hyperbolic
navigation.
NEW RSDN-20
transmission sequence by frequency
|
Segment
nr. station
Frequency kHz |
1
|
2
|
3
|
4
|
5
|
6
|
|
F3p
14.881091
kHz
|
|
|
|
Novosibirsk,
Revda,
Seyda
|
|
|
|
F3
14.880952
kHz
|
Krasnodar
|
Khabarovsk
|
Novosibirsk
|
|
Seyda
|
Revda
|
|
F2
12.648809
kHz
|
Revda
|
Novosibirsk
|
Khabarovsk
|
Krasnodar
|
|
Seyda
|
|
F4
12.090773
kHz
|
|
Revda
|
|
|
|
|
|
F5
12.044270
kHz
|
|
|
Seyda
|
|
|
|
|
F1
11.904761
kHz
|
Novosibirsk
|
Seyda
|
Krasnodar
|
Khabarovsk
|
Revda
|
|
NEW
RSDN-20 sequence by transmitter site
|
|
1
|
2
|
3
|
4
|
5
|
6
|
|
Novosibirsk
|
F1
|
F2
|
F3
|
F3p
|
|
|
|
Krasnodar
|
F3
|
|
F1
|
F2
|
|
|
|
Khabarovsk
|
|
F3
|
F2
|
F1
|
|
|
|
Revda
|
F2
|
F4
|
|
F3p
|
F1
|
F3
|
|
Seyda
|
|
F1
|
F5
|
F3p
|
F3
|
F2
|
The RSDN-20 transmitter locations
The mysteries that is shrouding
the Alpha / RSDN-20 navaid system to most of the VLF amateur community
is also valid for the location of the different transmitters in the system.
The stations at Novosibirsk in the south-central Russia and Krasnodar at
the north shore of the Black Sea are close to the two respective towns.
The far east station are north of the town of Khabarovsk, close to the
village of
El’ban, and NOT at Komsomolsk-na-Amur.
El’ban, and NOT at Komsomolsk-na-Amur.
The station at the Kola peninsula
are near the village of Revda, quite a distance from the port of Murmansk.
And finally there is the only station outside the Russian border, outside
the town of Chardzou, near the village of Seyda ( the Russians spell it
Seidi ) in Turkmenistan. This Alpha / RSDN-20 transmitter is most likely
not active as the Russians have problems with it.
But there can be changes of
transmitter sites in the future and even today the best way to be certain
of the actual positions of the transmitter sites are by Radio Direction
Finding. This should be the rule for most of the interesting
transmitters on the VLF band. Take a look at the RDF PROJECT. Radio Direction
Finding is fun, interesting and not at all difficult, join in and see how
this really should be done.
A.) NOVOSIBIRSK
55:45:22.0
N 84:26:52.4 E
B.) KRASNODAR
45:24:17.9 N 38:09:29.0
E
C.) KHABAROVSK
50:04:23.9 N 136:36:24.1
E
D.) REVDA
68:02:07.8 N 34:41:00.0
E
I.) SEYDA
39:28:16.0 N 62:43:07.3
E
 |
 |
|
|
The
location of the Alpha / RSDN-20 transmitter at Revda on the Kola peninsula
in Russia.
|
The
location of the far east Alpha / RSDN-20 station at the village of El’ban
north of Khabarovsk.
|
The RSDN-20 frequencies
I shall not delve into the details
of hyperbolic navigation, but the reason for the mathematical relationship
between the transmitter frequencies are bound up in the navigational purpose.
The determination of the exact signal characteristics is an interesting
mathematical puzzle. For the mathematical minded of you this is as easy
as a piece of cake. There is another way to make out the exclusive Revda
F4 frequency with another base number ! Can you find it ? The base harmonics
that build up each signal are seen to be separated by 1 /( 3.6 sec ) or
0.27777….. Hz, but are not integer multiples of 0.27777…..Hz. Are there
exceptions to this rule ? The operational RSDN-20 system frequencies are
mathematical related to a base frequency of 744 1/21 Hz.
F0
744 1/21
Hz = 1MHz / 1344
F1
11904.76190
Hz = 16 x F0
F2
12648.80952
Hz = 17 x F0
F3
14880.95238
Hz = 20 x F0
F3p
14881.09127
Hz = F3 + (5/36)
F4
12090.77381
Hz = (260/16) x F0
F5
12044.27083
Hz = (259/16) x F0
There is also a set of very
rarely used alternate frequencies which are multiples of 781.25
Hz
F6 12500.00000
Hz = 16 x 781.25 Hz
F7 13281.25000
Hz = 17 x 781.25 Hz
F8 15625.00000
Hz = 20 x 781.25 Hz
 |
Alpha
secondary frequencies.
This is a very exclusive capture
of the Alpha / RSDN-20 secondary frequencies. The signal was received at
my QTH on the 2.nd of June 2000 at 0947 UTC. Seconds later Alpha went QRT
for unknown reasons. The station transmitting is Revda on the Kola peninsula
in north-western Russia.
|
The four different frequencies
are the tree known secondary frequencies, 12.500 kHz, 13.281 kHz and 15.625
kHz together with a new, previously unlisted, Fx on 12.700 kHz. Note the
weak continuous background signal at 15.625 kHz. This transmission is very
often received at my QTH. The transmission is unidentified and
most likely not a regular part of the Alpha / RSDN-20 system sequence.
Sudden phase shifts at
2100 UTC – 0000 Moscow time
Every day at 2100 UTC there
are sudden phase shifts, these occur simultaneously and with the same phase
shift on all stations. There is also another phase shift with the phase
of each individual pulse to time the shift relative to 2100 UTC. Since
there is not an integer number of cycles of each carrier in a 24 hour day,
these phase shifts appear to be there to reset to zero phase at the beginning
of each day.
These shifts are 360°/7=51.4°
for F2, 2x360°/7=102.9° for F3 and 3x360°/7=154.3° for
F1
Early Soviet RSVT-1 receiver
Not easy to find info on this
one, but the receiver PIRS-1R is discussed in detail in a 1974 textbook
intended for students in the Soviet maritime academy. The receiver weighed
226.5 kg and consumed 1.3 kW ! In the receiver a synchronized commutation
module detected the first pulse of the master station and drove five mechanical
drum commutators with positions for each pulse in the epoch. The frequency
of a quartz crystal was automatically tuned to the master station via a
servo-driven variable capacitor. The phase of the master at one of the
common navigation frequencies was measured and stored via a phase discriminator
and a motor-driven phase rotator during the appropriate segment. Similarly,
the master phase at the difference of the two navigation frequencies was
stored during another segment. Then during the other segments, the slave
phases at the common and difference frequencies were measured and stored
with identical hardware, which also drove indicator dials and counters.
Phase propagation corrections and fixes were accomplished manually.
The future for Alpha / RSDN-20
No one knows ! For the time
being ( 07072000 ) are the system only partially operating. But this is
not uncommon, there have been very long maintenance periods in the past.
The future for this kind of navigational system don’t look bright. Even
though the operational expenses are low ( for comparison : the eight Omega
station costed only a total of $ 12M / year ) some “evil tongues” in the
UK have been speculating in the closure of the Alpha / RSDN-20 system because
of unpaid electricity bills. ! There is also a lot more to be written on
Alpha, but that will be the issue of an update.
A large thank you to:
Benjamin
B. Peterson and Lori
A. Constantino at U.S. Coast Guard Academy
for valuable information.
Väinö
Lehtoranta in Finland, Manfred
Kerckhoff in Germany and Dave
Oxnard in Holland for valuable information
and great inspiration.
Renato
Romero for great inspiration and the idea
of the Open Lab, Radio Below 22 kHz.
The
former Soviet Union Military Community for constructing Alpha / RSDN-20.
The
WEB for being there.
If you
have information or questions regarding Alpha / RSDN-20 or related topics,
feel free to mail to: Trond Jacobsen trond.jacobsen@halden.net