Russian Woodpecker: antenna complex

Very cool. I love the detail of the birdcage elements, and their SIZE! I'd love to climb them too. Well, I could have thirty years ago. Okay, I'd have been shot, but still.

The waveform sounds like a helicopter, but I'd like to see a FFT of the envelope over a day or so. I'm seeing several superimposed sinusoids there.

Uh...

Ah, a high-risk type then. Also cool.

Mark L. Fergerson

At least some observers at that time reported simple PRN (Pseudo Random Noise) sequences.

Do we know what the ERP and related figures were for this thing?

Over the horizon radar. At the time there were quite a few complaints about transmissions. I doubt there was any pseudo-random aspect. Just whatever was needed for early detection of ICBMs.

Start here: "The Duga systems were extremely powerful, over 10 MW ..." That's EIRP. Lots of photos online: but I couldn't find any detailed specifications beyond these:

This one is even bigger:

A simple countermeasure is to record the radar pulse, then play it back with a delay. If a ballistic missile does this, it shows up as a small nearby missile, and a large farther-away missile). That can be counter-countered by targeting the nearby blip, so a better countermeasure is to predict the next radar pulse, and spoof a nearer location.

So, some kind of unpredictable modulation is beneficial, if there is any antimissile defense.

That might work, if there were only one receiving station, fooling two or more receivers at different locations is much more complex.

Not much antimissiles in those days. When approaching missiles are detected, fire all missiles you have against enemy cities for MAD (Mutually Assured Destruction :-).

The Nulka system is still used to defend ships by confusing the radar of incoming missiles. Bit different job to fooling ground stations however.

I recall an article describing each pulse as carrying a few-bits code. This because the pulse period was faster than the max time-of- flight delay. Pulses reflected from objects with different ranges would be received simultaneously, then sorted out via the "id tag" on each pulse. Or, long-delayed pulses caused by odd ducting or ionosphere reflection would have a "stale" id tag, and could be ignored.

There is not much need for OTH radars to detect ICMBs, which fly high above earth. In order to detect cruise missiles and low flying bombers OTH is more useful.

During that era, quite a lot of NATO medium distance missiles was stationed in Europe.

IIRC, in those days there was a Letter to the Editor to Wireless World magazine showing close resemblance between recorded signals and PRN generators, with shift register stage numbers given.

Of course, you do not want to reveal all your radar coding sequences to the enemy, just due to the risk of being recorded and countermeasures applied to it.

While not in full alert, just use some primitive sequences like PRN and save the secret codes for full alert situation.

During my conscript service, we were told not to use certain radars just for training purposes at certain times. Later on, I found out that some spy satellites were overflowing these high latitudes at those times.

For detecting ICMBs flying over the pole, conventional (but large) radars were required, e.g. the big radar in Greenland, but not really OTH.

Another reason for the PRN is to have a transmission long enough to contain enough energy to be able to detect it, but have precise timing marking, indeed for detecting different reflections as well. I think the length of the pulse was 31 bits or so.

That would also make it harder for an attacker to create false signals.

Yup. Sequences with good autocorrelation properties have been important in radar for a long time. The Artech House "Handbook of Radar" edited by Merrill Skolnik is a good read. To find out about the optics of the future, a good resource is the RF of the past. ;)

Cheers

Phil Hobbs

AIUI Soviet OTH back in the day was intended to spot ICBM's in boost phase just after launch from Kansas etc. because MAD.

Ours (sadly way behind the Woodpecker tech at the time) was looking for launches from Siberia. The DEW line in Canada was more or less backup for that.

For that, big binoculars and a landline would be adequate. Hardly sufficient warning though. Even the missiles we had in Turkey were too close to try to shoot down but no doubt they had spotters watching them as best they could anyway.

Again, AIUI, part of the fuss over the "Cuber missile crisis" was that we had no reliable way to detect launches from there (short of continuous, expensive U2/SR-71 overflights), and certainly no way to defend against them.

Gods, yes, every HAM I knew bitched about them.

I remember that too. Maybe not WW.

(Google...) Yes, it was:

(more articles referenced too)

I wondered at he time if, and how much, that had been redacted to hide just how they were giving away.

Sometimes I wish I'd kept in touch with some of the radar-specializing students I knew in USAF Tech School. They'd drop hints about stuff like that, then stop, look at each other, and change the subject.

At least I'd have been able to pretend I knew what was going on when I, as an AGE mechanic, got picked to guard a runway access gate during an alert in 1971.

I did get to offer to shoot some officers who wanted to use my gate though. That was fun.

Yabbut at least some of "Early Warning" was looking for launches, not "here they come, tuck your head...".

Mark L. Fergerson

bionerd also did some interesting videos there:

Any of these super high power radars have to contend with reflections from really distant objects. The US's DEW system picked up the moon on several occasions and nearly started war preparations, until they understood the phenomenon. Presumably the Russians saw the same effect. So, a scheme to jitter the timing between pulses in some simple pattern allows you to detect range beyond the repetition rate, by detecting that jitter in arrival time of the returns.

Jon

There you go! I would guess that the moon-return situation happened with a vintage radar which couldn't normally "see" beyond rep rate, unless you aimed it at the moon on a clear night ;-) ...Jim Thompson

There were some cases during W.W> II where shipboard RADAR picked up enemy ships that were detected by ducting. It was confusing, at first. They would send planes up, but couldn't find the enemy. They finally figured out that the display was from a previous pulse, instead of the last one sent.