The Russian Woodpecker Revisited

UPDATED 14 April 2024

A signal I couldn’t avoid hearing with my trusty BC-348, S-120 or HA-350 receivers was the Russian дуга Over The Horizon Radar (OTHR) that they had built and operated near Chernobyl in Ukraine.

It is still a popular topic all over the Interwebs. Here’s my take, plus some fun with satellite photos and a Slide Rule to explore some facts and myths about these systems:

Two other OTHR installations had been fielded by the Russians as they developed this system. The first, experimental one was located near the port of Mykolaiv on the Black Sea, the other in the Russian Far East near Komsomolsk. We probably heard all 3 at times.

The DUGA-1* system near Chernobyl was also known by many as “the Russian Woodpecker” for what its 10 pulses per second sounded like. From Wikipedia; here in 1984 interfering with the WWVH Time/Frequency broadcast from Hawaii. File courtesy Rolypolyman:

To me, it sounded exactly like a helicopter, the UH-1 Huey to be exact. Why? 10 pulses per second made by the blades of the 2-bladed helo rotor = 5 Rev/Sec. Times 60 seconds/Min = 300 RPM. That’s exactly the rotor speed of a Huey in normal flight. But I digress….

These radar pulses produced a massive level of worldwide radio interference to high frequency communications all over the mid-HF bands in the mid 1970’s to the late 1980’s. Those services included shortwave broadcasting, maritime, aviation, utility, military, commercial, navigation and scientific services. Also included were many frequency bands used by Ham radio operators such as myself. It also interfered with Radio Moscow itself.

It was also reportedly heard on wired telephone systems, stereos and car radios, especially in Europe.

дуга “DUGA” (Arc in Russian). Arc probably indicating its over-the-horizon mission. To achieve “long range” it used the ionosphere to bend its transmitted pulses back down, well beyond the curvature (horizon) of the earth. Something a conventional microwave “line of sight” radar cannot do.

Its signal was plenty loud in the U.S. at the time with its massive peak radiated power estimated at 10+ megawatts EIRP to 40 megawatts ERP (estimates vary). I’d like to see the azimuthal gain versus frequency plots. Has anyone modeled this complex array with EZNEC?

Note that the US/Canadian NORAD Command operated the DEW (Distant Early Warning) Line across the Alaskan/Canadian/Greenland arctic. It used line-of-sight microwave radars and was not intended for nor capable of “over the horizon” detection of Russian bombers and missiles. It was replaced by satellite-borne detection systems.

The gigantic DUGA-1 receiving antenna is 500′ tall and nearly a half-mile wide with its broadband cage dipoles fed by open wire transmission lines and linear wire reflector screens . There are actually 2 arrays here, one “small” and the other much larger. Likely for receiving high and low frequency return pulses respectively. I’d have to visit with a tape measure.

There are many You Tube videos of this antenna array and probably hundreds of online photos. Sadly, NONE of them were taken by an Electronics Engineer!

(I wonder if there is an SO-239 Connector on it somewhere. Just saying…)

The antenna array installation near Chernobyl. The individual towers seen at each end of each array support the hundreds of reflector wires which make the system uni-directional off to the northwest.

These reflector wires also reduce the effect of signal pulses arriving from behind it 134+ milliseconds later (after these powerful pulses circled the Earth at times). “Front-to-Back ratio”.

The Ignoraty and Conspiracy Whacko’s described its purpose as mind control, weather control, Russian HAARP, a death ray, an earthquake trigger, etc. (Actually, it does control their minds.)

Dude! Like it totally caused Chernobyl to freakin’ EXPLODE! and THEN Explain Hurricane Katrina to me. Huh! Huh!

CNN opined in a March 4th 2019 article that it has “a far more sinister and mysterious reputation.”   CNN continues: “its true purpose and the important details of its functioning are covered in mystery.”  (Umm no CNN, it’s purpose and function was EXACTLY understood – 40 years ago.) 

That CNN Travel article included a map with the locations of both the radar site and the Chernobyl nuclear power plant (reversed – ahem…).   “CNN: News you can trust”…

The radar sounded like that recording, a staccato pulse train of about 10 pulses per second, however spread over a very large bandwidth due to the fast pulse risetime. Where Bandwidth = 0.35/Pulse Risetime.

Individual pulses were observed having bandwidths of between 40 KHz and up to 800 KHz. This varied as the individual pulses contained variable BPSK modulation data.

It jumped around in frequency as they adjusted it to deal with HF propagation realities, appearing randomly at between 5 and 28 MHz (sources quote different limits at different times) with higher harmonics in the HF spectrum. Transmissions sometimes lasted several minutes on each frequency before they moved it to another.

Some obvious clues: The above 2 main DUGA-1 broadside antenna arrays (NATO variously Code named Steel Yard or Steel Work/s) were built along a carefully surveyed axis line of 053/233° True

Below: See Google Earth 51° 18.30N 30° 4.00E. (I used the “Line” Ruler tool to measure the azimuth with the yellow line that I inserted in this satellite photo along the array axis. Try it. It runs 053°/233° True) That orientation was no accident.

This is the receiver site; its abandoned/dismantled transmitter site is 57 km away to the northeast, built on that same 053/233° axis.

Which Way? The T/R system emits and then receives the reflected return signal at right angles to the dipoles/reflector wire arrays off to the northwest on an azimuth of 233+90=323° True. If you plot that Great Circle azimuth from the transmitter site, it goes over eastern Europe, Scandinavia, Greenland, Hudson Bay, Ontario then directly over the ICBM missile fields in north-central U.S. Check.

Nothing “sinister and mysterious” about it. It’s a Radar. The “target” was the US ground-based missile deterrent force they wanted to monitor.  “Important details”. How about range capability?

Timing is Everything With its 10 pulses-per second, the interpulse period is 100 milliseconds.  As every radar operator knows, radar pulses (radio/light) travel 328 yards per microsecond.  That works out to a one-way distance of about 18,000 miles before the next pulse is transmitted.  Since radar is a round-trip system, the max detection range is half that, about 9,000 miles before the next pulse is transmitted, deafening the receiver to any return echoes.

However, that 9000 mile distance (time available between pulses) has to include extended “side” trips up to the ionosphere and back, at least twice, likely 3-4 times. This depending upon the operating frequency, ionosphere height and density at the moment.  Also, the Transmit/Receive “T-R” switch that protects the receiver from the massive transmitted pulse needs some recovery time, as does the receiver itself.

So the effective detection range to a target would be still less; more like the 5,000 ground miles (8000 km) to the center of the ICBM missile fields from DUGA-1. Hence the 100 millisecond interpulse period. Check.

There CNN, solved if for ya.  “Important details covered in mystery” revealed by a kid with a 4-tube Hallicrafters S-120 shortwave radio, an old Heathkit oscilloscope and a simple slide rule. Of course the USG also had CORONA satellite or SR-71 imagery to confirm the structures.

Why there? They located the radar in the southwest part of the then USSR (in Ukraine) to try to minimize HF radio propagation disturbances over or near the north polar areas. These are caused by charged particles in the solar wind interacting with the Earth’s magnetic field which is concentrated at the poles. Think “Northern Lights” etc. Check.

I’ve chatted with dozens of Russian Hams over many years from locations throughout the US; HF radio propagation over the north pole is certainly problematic. HF morse code (pulses) arriving from Russia via the ionosphere have a very characteristic and well known polar/auroral instability known as “flutter”. This is caused by multipath through the chaotic ionospheric medium above the north magnetic pole. All day every day.

Below is a QSL (contact confirmation) post card I received in 1977 from Vlad, at club station UAØCDS from a morse code contact I had with him “over the pole”. Note that his classic Soviet era (Government-Approved) QSL card illustrates the shimmering green Northern Lights curtain above the Reindeer sleigh.

Probably common sights in his local area. Vlad was in the Siberian city of Sovetskaya Gavan, in the Russian Far East, (coincidentally about 150 miles from DUGA-2). My signal would also have had that characteristic “flutter” as he received me. When you hear it, you immediately know the station is over the pole in Russia or even India or Southwest Asia.

(The DUGA-2 installation at Komsomolsk operated along an azimuth of 40.0° True, also aimed directly at the same ICBM sites in the north-central part of the U.S. The Russians also selected the Far-East site as it mostly avoided unstable ionospheric propagation conditions over the north polar regions.)

High Frequency Direction Finders (HFDF) systems (and eventually even Hams) had accurately located the transmitters at the time.

Powering the OTHR System: Ohm’s Law would suggest that DUGA-1 was not built immediately adjacent to (15 km from) the Chernobyl nuclear power plant (NPP) to provide it with limitless electrical power as many have asserted. (Mind-controlling Death Rays and Earthquake Triggers DO require enormous power however.)

This is the receiver site which would consume relatively little power as compared to the requirements of the massive transmitter located much further away. Even then, the estimated 10 MW pulse transmitter with its roughly 3% Duty Cycle (3 millisecond pulses spaced 100 milliseconds apart) = 300 KW average. That, plus assumed inefficiencies would barely be noticed by the 3500 megawatt capacity of Chernobyl with all 4 reactors operating.

It is more likely that particular receiver site was selected in Ukraine to be in proximity to suitable housing and civil infrastructure (Occam’s Razor applies). The nearby (doomed) town of Pripyat had been build to support the nuclear power plant construction and operations. Both installations would require large staffs. Kyiv was also relatively close by.

Today there are remains of a single 3 phase power pole line heading directly from the Chernobyl NPP transformer/switch yard to the south towards Kyiv. There is a visible tap 4.8 miles down this line which then heads southwest over to the DUGA receiver site. Recognizing that this site was built several years after the power plant and its national power grid connections, that tap makes sense.

The transmitter site looks to be powered by the local grid in nearby Chernihiv rather than by the Chernobyl NPP directly. It is easy to follow the (only) twin, 3 phase power pole lines and associated service roads leading WNW from that city over to the transmitter site 40 km away. No power lines are seen heading from Chernobyl to the transmitter site or any other power lines leading to the transmitter..

Propagation studies: Today there are the remains of a what appears to be a small Wullenweber-type or related CDAA direction finding receiver antenna nearby. The site is 1.6 km SW of the receiver array along nearly that same 233° array axis. Thus also putting it in the DUGA transmitter antenna system pattern side-null to protect it from the transmitter pulse energy.

That HFDF (NATO – FIX 24?) site is generically known as a круг “Krug” (circle in Russian) and has been reported to possibly include an ionospheric chirp sounder. Makes sense – queuing DUGA to the optimum frequencies for operation. The word азимут (azimuth) is not surprisingly seen on an interior control panel photo. Indicating to me that this detects favorable propagation paths both in frequency AND direction, 323° true being the most interesting to them at this DUGA installation.

It would be used to measure the variable ionospheric height as that is essential to knowing where your signal is going to/coming from.

(DUGA-2 in the Far East also has a CDAA antenna array 3 km away from that receiver site, similarly in the transmitter antenna side-null to protect it. There are remains of a similar CDAA antenna installation at the receiver site in Mykolaiv. These are also presumably ionospheric sounders used to queue the operators to the optimum frequency/azimuth of operation.)

OSINT doesn’t seem to report if the Duga receiver antenna system or its associated transmitter antenna was actually designed to be a steerable phased array or more simply a fixed directional system. That would cost them complexity and Gain. Also, their intended radar targets didn’t move much in azimuth. No need.

Without seeing photos (taken by an EE or RF Engineer) of how all those open wire transmission lines are terminated I cannot determine. Pulse analysis indicated it might have a range resolution of perhaps 10 miles but did they need good bearing resolution? The ionosphere is big, squishy and always moving. “Komrade! Is that a missile or Montana?”

FUN FACT: I noticed when DUGA often shifted into the internationally allocated Amateur Radio ham bands (in violation of international law which the Russians signed: nothing to see here, move along). When it showed up with impunity that 10 PPS signal obliterated all communications on those frequencies.

When THAT happened I found myself needing to test my transmitter and electronic CW keyer on frequencies allocated for ham radio use. Testing my keyer at 10 dots per second, or thereabouts, on the DUGA frequency, or thereabouts, I could often get them to move off frequency (coincidence?). My puny 40 watt Hallicrafters transmitter CW signal was significantly stronger than any reflection they could detect off a missile, exhaust plume, disturbed patch of ionosphere, aircraft or maybe even the North Dakota ground clutter.

Doing my part in the Cold War…LOTS of other Hams tested their equipment in a similar manner. “Woodpecker Hunting”…

Must have driven their operators crazy as it was apparently fairly easily “discouraged”, accidentally of course. I don’t know what kinds of pulse-forming networks** or signal processing in the receivers they used at the time but it was probably adequate given the technology available. Receiver transversal matched-filter gymnastics notwithstanding.

** Russian engineers were/are particularly good at designing pulse forming networks and pulse power machines. Apparently not so good at operating nuclear power plants.

My chirpy Novice transmitter pulses probably looked like up-doppler shifted INCOMING! “Komrade Kononel! They launched!” “Nyet, that’s just Tim again”.

Enterprising Hams designed filter circuits and even sold the “Moscow Muffler” Woodpecker filter and others for Ham/shortwave receivers. It was only partially effective because the Russians (and especially the ionosphere) caused random changes in the received signals. Hard to keep up.

The DUGA-1 site was abandoned in 1989 due in part to significant radiation contamination from the explosion and melt down of the Chernobyl nuclear power plant (and the implosion and melt down of the “Union of Soviet Socialist Republics” and the Communist Party).

There is wide speculation that the Russians abandoned the system because “it didn’t work” (“work” being undefined). Not so fast. This technology does “work” within the limits of physics, the state of the art and Operational constraints. OTHR signals can still be heard in parts of the HF spectrum, including in Ham bands.

The US and several other countries are operating OTHR systems today. That includes Russia with its relatively new “Kontayner” OTHR systems and its significantly different antenna arrays. What’s old is new again. But that one is another story. Individual Russians are capable of some good science and engineering.

(UPDATE 4/12/24: During Ukraine’s counter attack against the Russian invasion, Ukraine launched a 650 km drone strike that hit the Russian Kontayner OTH radar receiver site at Parapino, Mordovia. BDA pending.)

Today, all 3 DUGA transmitter and associated receiver sites have been abandoned, collapsed and then looted for scrap. However the Chernobyl system receive antenna still stands and is now a local tourist attraction. The other sites and infrastructure are gone, being reclaimed by the forests.

The above-mentioned 2019 CNN article closed with this: “The Soviet Union may have gone forever but its ghosts still haunt Ukraine.”

Indeed.

For some really excellent analysis and background on “DUGA” be sure to take a look at Ringway Manchester’s series on Youtube about this and other communications topics.

* I’m going with DUGA-1 for the Chernobyl installation. “Open sources” widely disagree on the number suffixes of these 3 DUGA systems, seemingly randomly assigning them by location. Not helped by Russian political warfare “Active Measures” programs including military deception (maskirovka) and disinformation (dezinformatsiya) campaigns. At the time they identified this site on Russian maps as a “Childrens Camp”. Of course they did. There was such a camp nearby, close enough.