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G0FTD > SWL 20.04.05 01:02l 173 Lines 9018 Bytes #999 (0) @ WW
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MYSTERY SOVIET OVER-THE-HORIZON TESTS
Wireless World - February 1977
It is now common knowledge that a large portion of the h.f. band of the
radio frequency spectrum has been suffering for over the past few months
from interference caused by a very powerful transmitter, or transmitters,
located somewhere in Russia or the Ukraine. The interference became so
bad that most of the communication services within the band have
complained, through their respective organisations, to the Home Office
and to the Frequency Registration Board of the International
Telecommunication Union (ITU). Other countries (including the USA) who
have been similarly affected by the transmissions, have also forwarded
complaints to the ITU and the Russian Authorities.
A Home office representitive recently informed "Wireless World" that
they have made a complaint direct to the Russian authorities and have
been told that they are conducting tests and are taking steps to reduce
the interference.
What we, the public still do not know, and are not likely to be told,
either by the Russians or our defence organisations and industries,
if they know, is what these tests are for. We can only speculate, and
perhaps the best way to do this is to study the information at hand and
then compare it with systems which we know are within the realms of our
present technology.
Reports indicate that the transmitter is located in the town of Gomel,
an industrial town in Byelo-Russia (See Pat Hawker's comments, November
issue), and this, according to a recent "Daily Mail" report, has now
been confirmed by NATO direction-finders. Monitoring station engineers
agree that the actual powers involved are in the tens of megawatts and
Mr Dafydd Williams, chief engineer of the BBC External Broadcasting is
reported to have estimated them as 20 or 40MW or more, and audible in
every part of the globe.
Some American publications have claimed that the interference was first
brought to the attention of the Federal Communications Commission (FCC)
in July, principally by radio amateurs. Mr S. A. Cook G5XB of Intruder
Watch (1) told "Wireless World" that the transmissions, which have a
pulse configuration with a basic pulse-repetition frequency (prf) of
ten per second, occur between about 5 and 22MHz, are widely scattered
and appear to depend on the maximum-usable-frequency (m.u.f.) for
propagation.
For example, at dawn they can be expected between 14 and 22MHz and by
3 p.m. they may be at 14MHz or lower. When the interference first started
it persisted for 10 to 12 hours at a time and, at one stage, completely
obliterated the 14MHz amateur band. Another report, said to have come
from the BBC, indicated that Cairo Radio had also been obliterated.
However, a spokesman for the BBC monitoring station said that while this
was an exaggeration the interference has been a considerable nuisance
and has occasionally made monitoring impossible. Their experience of the
interference was that it appeared at various times, on different
frequencies and for varying durations within the the range 6 to 15MHz.
A representative of the Home Office international monitoring station
completed the picture by saying that the signals have been affecting
frequencies from 4 to about 27MHz - almost all of the h.f. band.
Amateurs and broadcasters have not been the only ones to be affected by
the interference; almost every service has been troubled - except the
television services, which are on higher frequencies. Public services
such as Post Office radio communications have experienced interference
and so have h.f. maritime communications. It would be unrealistic to
suppose that these high power signals have not had some effect on the
h.f. military services too.
According to Mr Cook, the period of the 10p/s signal comprises a pulse
train of up to 20 different squarewave pulses, some less than 2ms in
length - an estimated pulse frequency of at least 800 pulses per second.
Although the signals are very difficult to observe, even on a high-speed
oscilloscope, he is convinced that there are as many as four sources
all transmitting the same, or very nearly the same information, perhaps
from different locations. What is equally interesting is that the signals
are no longer remaining for periods of hours in one frequency band but
are moving up and down the h.f. spectrum in about 100kHz steps, remaining
at the chosen frequency for 30s to 10min.
The use of pulse signals suggests either over-the-horizon (o.t.h.) radar
or communications. In either case a complicated system would be necessary
to compensate for propagation variations, and this may involve the use
of one or more source. The variations in carrier frequency could either
be an attempt at remaining at the most propagatable frequency or they
could be a security procedure. It is understandable that the Russians
should wish to keep h.f. communications in addition to satellite
communications using microwaves because, in the event of war, the
satellite is very vunerable. However, it is not clear why tens of
megawatts would be needed, even for communications to submarines.
Over-the-horizon radar seems to be far more probable. This is not new,
(2) the USAF and the Defence Advanced Research Projects Agency (DARPA)
have been actively interested in o.t.h. radar for about 15 years and
distances of at least 1850km are possible.
It is interesting to note that the frequencies chosen for o.t.h radar
are normally between three and 30MHz. The system would almost certainly
use o.t.h.-b. (backscatter) radar which depends upon energy reflected
from the target reaching a receiver antenna array via ionospheric
reflections.(2)
Radar of this kind is often ineffective within a certain skip distance
from transmitter.(2) This may explain why an American radio amateur
visiting a Soviet amateur organisation as a representative of the ARRL
was told that their amateurs were unaware of any high power transmissions
from their country.
Systems using more than one radar source are also in existence today.
These multiradar tracking systems (3) use some of the signals received to
update others so that the best estimate can be made of the target
position.
Although it is argued that 10p/s is too slow for tracking anything but
ships, the higher frequency components within the basic pulse train
could surely contain enough information for faster moving, smaller
aircraft - especially using multiradar.
If the Russians are really being adventurous they could be testing a
four-source system capable of detecting the actual shapes of their
targets. Recent results in the study of electro-magnetic impulse response
of objects (4) have indicated that the information required for the
determination of the approximate shape of the objects can be contained
in the low frequency range, where the wavelength is longer than the
overall dimensions of the object. This means that the h.f. band could
be used for targets from 120m down to 10m length or less and this would
include the majority of aircraft and rockets.
It is also interesteing to note that the most troubled frequency (14MHz)
corresponds to 20m, about the size of an aircraft.
The study (4) showed that "below four frequencies are sufficient in most
cases to provide reliable classification in the presence of substantial
amounts of noise". Using only four frequencies or less, the study showed
that four aircraft models (F-104, 18.24m long by 16.6m wingspan, F-4,
MiG 19 and MiG 21), scaled to approximately the same size, could be
reliably identified. In comparison the distinction between winged
rockets and other aircraft would be a simple matter.
Is it feasible that the Russians are testing a system which incorporates
both o.t.h. radar and shape recognition by radar returns? The most
likely targets for such a radar would be the US B-1 swing-wing bomber
and the Navy and US Airforce cruise missiles (only 4 to 6m long).
Positive identification of approaching B-1 bombers and cruise missiles
would be a valuable asset to the Russian forces and would probably be
worth any diplomatic embarrassment caused by interference with Western
radio services during preliminary trials.
REFERENCES
(1) Intruder Watch is an organisation which monitors the amateur frequency
bands and reports to the Home Office any persistent intruders within
those bands. In the UK there are currently 22 observers reporting an
average of 100 serious intruders per month in the amateur bands alone.
Throughout the world the figures are nearer 1200 per month.
(2) Janes Weapons Systems
(3) Tracking in a multiradar environment, H. W. Thomas, G. Maignan and
J. T. Story, "Proc. IEE" Vol. 123, No. 3, March 1976.
(4) Identification of complex geometrical shapes by means of low frequency
radar returns, Y. T. Lin and Professor A. A. Ksienski, "The Radio And
Electronic Engineer" Vol. 46 No. 10, October 1976.
Transcribed from the original article by Brian Rogers April 2000
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