Over-the-Horizon Radars Raising the Ire of European Monitoring Systems

[Lauri-CoyoteFrostbite]

Ah !, if life were only so easy, Smiles

.
With the limited information fed me, my conclusion- Jamming OTH radars is not a cottage industry.

My grandfather, a B24 bombardier with the 8th Air Force told me of their radar jamming techniques of WW2. They used 'chaff'- aluminium foil cut into thin strips that approximated the resonant wavelengths of the German radars.... And they dump'd cardboard boxes full of it nearing the flak zones- hopefully confusing the anti-aircraft gunners' radars.

Too bad today he's not around to see his grand daughter when she test'd platforms like DRFM--Digital Radio Frequency Memories, also know colloquially as "Spoofing."
Spoofing is a technique of confusing a radar by replaying their pulses back to them with a delay. This makes their target appear to be moving when in fact its may not be. It can also fool the other radar into thinking there are multiple targets. Neat stuff, No ?
The US Navy is into this with their electronic warfare programs.

My knowledge pretty much ends there. Out in the Nevada deserts we tested out the RF sections, using dummy algorithm's- but when the real test days came, and the "Brand X" boys showed up, I was politely asked to stand down. They disconnected our software and plugged in their own Black Box.
They let me watch the flashing lights, hear the bells and whistles- but I knew enuff not to ask them questions


If OTH systems are anything like my microwave platforms, they are far far advanced of being fool'd by my grandfather's box of aluminum foil.

Lauri

 

[dlwtrunked]

Interesting article with its list of frequencies.
...
I remember oh-so-well those high power Soviet era OTH radars

Lauri

Unfortunately a link to an article I wrote about the USSR system back in 1985 (seems not that long ago) has disappeared from the link (Link #1) to it at https://en.wikipedia.org/wiki/Duga_radarhttps://en.wikipedia.org/wiki/Duga_radar
But here is part of it (keep in mind that more precise locations were only later known):
It should be readily realized in the radio hobby that what is one man's interference is another man's interest. Such is the case with the USSR OTH-B (over-the-horizon backscatter) radar. Also known as the "woodpecker" or "pulsar," this device has drawn much interest by the interference that it generates. In fact, the WORLD RADIO TELEVISION HANDBOOK'S 1984 edition reviewed two products designed to counter this interference. On the other hand, with proper equipment, the woodpecker can be an object of study -- as it is to this author. The USSR OTH-B radar is believed to use two locations in the western USSR, Minsk amd Nicolayev, one location is used for transmitting and the other for receiving. This prevents the receiver site from being "overwhelmed" by the transmitted signal. (This is a common practice for many operations at HF frequencies.) An analysis of the woodpecker has been made using an externally triggered scope. The remainder of this article discusses the results of that analysis. The USSR woodpecker has been observed using three repetition rates: 10 Hz, 16 Hz and 20 Hz. By far the most common rate is 10 Hz. In fact, the 16 Hz and 20 Hz modes are so rare that an analysis of those modes has not been made; however, it is probable that their operations are the same as those of the 10 Hz mode. The woodpecker generally is found to operate in either of two modes which will here be called STATIC MODE and DYNAMIC MODE. In the STATIC MODE, four frequencies are used, each of which is associated with one of the time windows during which a pulse is transmitted. For example, the woodpecker was observed using 16450, 16490, 16570 and 16390kHz.
During time window 1, 16450 transmitted a pulse; during window 2, 16490 transmitted a pulse, during window 3, 16570 transmitted a pulse; during window 4, 16390 transmitted a pulse; then the 72 ms silent period; and then the pattern repeats. Before going any further, let us note an important fact. The pulses transmitted by the woodpecker have a wide bandwidth typically 40 kHz; thus, all listed frequencies are approximate. The shape and length of the pulse is not known. The pulse does not occupy all of the 7 ms transmission window; measurements indicate the pulse width to be between 3 and 6 ms; possibly it can be varied. It would not be surprising if the pulse actually consists of several "sub-pulses" due to reciever reaction time and multipath, it is very difficult to analyse the exact structure of the pulse.
In the DYNAMIC MODE each of the four frequencies uses all four transmitting windows, stepping through them in 6 ms intervals.
In the 10 Hz mode, a pulse is transmitted every 0.1 sec. (100 ms). Using the triggered oscilloscope, it is found that there are actually four adjacent 7 ms transmission windows in the 100 ms period. In time order, let us call these 7 ms transmission windows 1, 2, 3 and 4. In other words, we may view the 100 ms period as consisting of window 1 (7 ms), window 2 (7 ms), window 3 (7 ms), window 4 (7 ms), and the remaining 100-28=72 ms in that order. The stepping order on each frequency may be 1 - 2 - 3 - 4 or 4 - 3 - 2 - 1 so that each frequency occupies a different transmitting window during a typical six second period.
As an example, the dynamic mode was noted using 8070, 8230, 8310 and 8260 kHz.. In the first six seconds, the transmission-to- transmitting window assignment was 8070/1 8230/2 8310/3 8260/4; for the next six seconds it wa 8070/2 8230/3 8310/4 8260/1;
then for six seconds it was 8070/3 8230/4 8310/1 8260/2; finally, for six seconds it was 8070/4 8230/1 8310/2 8260/3.
The pattern then repeats after 24 seconds (4 steps x 6 seconds). The result is that the dynamic mode looks like the static mode for six second intervals. Only to a very trained ear can the difference between dynamic and static modes be detected.
It is suspected that the loss of synchronization that sometimes occurs with woodpecker blanking devices is caused by the transmitting window shifts in the dynamic mode, not by varying rate as stated in the WORLD RADIO TV HANDBOOK.
Why does the dynamic mode use both the 1 - 2 - 3 - 4 and 4 - 3 -2 - 1 transmitting window cyclings? The answer came one day when, 15960, 16370, 17480 and 16820 kHz were observed using the 1 - 2 - 3 - 4 cycling, while 16230, 15730, 16020 and 16130 kHz were using the 4 - 3 - 2 - 1 pattern. Keeping in mind the wide bandwidth of these signals, it is likely that the two different cyclings allow simultaneous use of two separate four-frequency, dynamic-mode systems in the same frequency band without mutual interference. However, usually only one set of four frequencies has been noted at a time.

COMPLICATIONS
In either the static or dynamic mode, one or all frequencies may suddenly change, often so rapidly as to frequently make it difficult to establish which four frequencies are in use at a given time. Sometimes the woodpecker returns to a frequency abandoned earlier.
No pattern has been found for these frequency changes; they appear to be random. At times the frequencies stay constant for long periods; at other times the frequencies change at such a rapid rate as to make analysis difficult.
While a listener may encounter difficulty trying to separate two overlapping woodpecker frequencies, a triggered scope will easily identify the two signals. On rare occasions the woodpecker has been noted with other 10 Hz modes, often consisting of more than one pulse. In one instance, the woodpecker was observed transmitting pulses in all four 7 ms transmitting windows on a single frequency. This could be described as static or dynamic mode with all four frequencies the same. In another case, the woodpecker was found to be transmitting a second pulse 23 ms after the first; in effect, this made eight transmitting windows. This operation was of the dynamic type. Whether these rarely seen modes are actual operating modes, test or tuning modes, or accidents, is unknown. Perhaps other modes or some of the questions that arise from the above analysis may be answered by further observations.

 

[poltergeisty]

So an over the horizon radar is suppose to track a B-2?

 

[Lauri-CoyoteFrostbite]

A B2 ?..... what's That ?!

 

[majoco]

The Northrop-Grumman B2 is supposed to be a "stealth bomber" as most of it's surfaces are designed to not reflect an incident radar wave back the way in came from - therefore perhaps being undetectable.

 

[k7ng]

"Crows"
As in "Association of Old Crows"?
I was one.
OTHR has some really fascinating technology.
As yet, I don't believe there is any other means, including space-based, that can observe a large volume of un- or under-inhabited surface of the earth 24/7/365.
OTHR can simultaneously provide data that allows inference of surface wind and sea state along with whatever else is being looked for waay out there in the ocean.
Fascinating true story, never satisfactorily solved (in accessible files, at least), look up "AN/FPS-95".

 

[Lauri-CoyoteFrostbite]

.
Smiles Martin---
.
I was being a wise azz-- though so often I have received very similar answers when asking sensitive questions- kind'a the jargon for "Don't ask again if you know what's good for you... "

( That's a great pixur of the bomber. )

Not long ago I got to see a B2 up close at Andrews AFB (Maryland.) At least they let me walk around it- with an armed escort- despite my security clearances.

I can say it is a very elegant aircraft- much smaller than many would think- sleek , with the beauty of a raptor.

......................They wouldn't let me sit in it...


Lauri

 

[ladn]

Not long ago I got to see a B2 up close at Andrews AFB (Maryland.) At least they let me walk around it- with an armed escort- despite my security clearances.

So much for getting up close and personal with the electronics bays.

 

[AK9R]

Meanwhile, back to OTH radar.

 

[Token]

I have had the privilege of attending, as a neophyte, some presentations on Over the Horizon radars.

The first radar I worked on professionally was an HF OTH-B. However, since 1979 most of my radar, and counter-radar, work has been at VHF and up frequencies.

"Microwave radar has a range of 180-200 mile range. Over the Horizon systems reach a much greater distance; from sea level upwards, and with a range of about 2000 miles. Its major drawback is its resolution-- it does not approach the detail of a microwave platform.

I think it would be more correct to say microwave radars, being generally line-of-sight, are limited in range by a combination of their design parameters and the distance of the radar horizon, this horizon determined primarily by the curvature of the Earth.

A microwave radar may be capable of detecting and tracking targets at hundreds or thousands of kilometers (assuming its PRI is sufficiently long or it has an ability to distinguish n'th time around targets, its receiver is sufficiently sensitive, and its ERP sufficiently high), but unless that target is high enough to have LOS it will be below the radar horizon.

A LOS limited microwave radar antenna 10 meters high would have to be looking at a target 10000 meters high to detect it as above the horizon at 425 kilometers. So even if the radar was technically capable of tracking such a distance most targets would be undetectable, below the horizon, at such ranges.

Of course, HF OTHRs get around this issue by either using sky wave and the ionosphere to see around this corner, or by using surface wave propagation.

And then there are also VHF and up OTHR radars, but that is a different subject, much more niche and specialized. Kind of a lost 50's and 60's thing, really.

what would be the effect of say a half dozen hams, each simultaneously transmitting about 5 KHz apart in the middle that "40 to 80 KHz wide over the horizon radar" band? It's been a few years since I wrestled with signal theory, but I think at some point enough notches would seriously degrade the OTH radar performance?

There is no simple yes or no answer, there are far too many variables.

These radars have beam steering, often both on transmit and independently receive, to direct the beam in desired directions. Used in conjunction with current propagation conditions and selection of operating frequency they can illuminate / monitor / optimize a specific target region of the Earths surface. Unless all of the offending signals are in the / a target region they will naturally be reduced / rejected as signals outside the beam.

Just because you can hear the radar, even hear it very loud, does not mean the radar is actually looking at your region, it may be looking someplace else totally, and you are only hearing sidelobe or scattered energy.

So the radar may be looking away from the jamming hams, reducing their effectiveness.

And then what kind of signal is being sent by the group of do-gooders? CW would be very ineffective, as would rapid CW dits or any narrow band digital modes. Broadband random noise would be more likely to get a result. The most effective would be intelligent techniques based on the transmitted radar waveform. For example, match the chirp rate of the radar and send back false targets that would fall within the Doppler and Range bins. With GPS timing this would not be horribly difficult.

However, in the US, such coordinated activity would be illegal and the more coordinated the more easily recognized. You cannot intentionally jam any signal, even if you have the right to use the frequency and the offending signal does not.

But yes, assuming you are actually in the target area being illuminated by the radar (or have sufficient power to impact his sidelobes), and assuming you picked a suitably wide noise source or intelegent signal, you could, indeed, make such a radar move or reduce its ability to use a specific frequency range. In general it is going to be difficult to meaningfully coordinate the signals involved, half a dozen folks setting on frequency yelling or whistling at the mic is probably not going to do it.

T!

 

[Token]

So an over the horizon radar is suppose to track a B-2?

One of the advantages to HF radar in general is its ability to reduce the advantage of low observables. This is a known fact, and is basic physics.

Periodically some smart writer will get ahold of the fact that stealth aircraft are generally less stealthy at lower frequencies. Then articles will appear claming Stealth has no value, since HF (or VHF, or UHF, or whatever that writer goes with) radars see right through it.

All of this was well understood before the first intentionally reduced radar cross section aircraft flew. Reading a few basics about RCS, RCS reduction, and how RCS calculations break down once you exit the optical region will show anyone at least the basics of why and how this is. Look at predictions for RCS in the Rayleigh region, Mie region, and optical region for further understanding.

At its most basic level, the modern implementation of stealth comes down largely to shape and surface.

Shapes (both gross shapes and fine shapes) are selected to reflect radar energy anywhere but back towards the radar. And this tends to work well across wider frequency ranges, down to the frequency range where pieces / parts of the target become resonant and up to a frequency were smaller features become resonant.

Surface is another problem all together. You can design surface coatings that absorb or conduct, rather than reflect, RF signals. But they tend to do so over very narrow specific frequency ranges. And at a gross level the thickness of this coating is related to its frequency response, so that such coatings tend to be more effective and robust as you go up in frequency.

All of this means that yes, a very good argument can be made that HF OTHRs can indeed see stealthy targets such as the B-2 bomber. This is one reason these radars have become so popular.

But, tracking a target, such as the B-2 or any other military target, is not the same as shooting it. And while you can build very low frequency detection radars, HF, VHF, UHF, etc, these radars are not well suited to actually engaging a target. Tracking and shooting radars, radars that can guide missiles, guns, or other aircraft onto a target, all tend to, for a variety of physics based reasons, be higher in frequency. Frequencies at which stealth techniques are very effective.

T!

 

[poltergeisty]

One of the advantages to HF radar in general is its ability to reduce the advantage of low observables. This is a known fact, and is basic physics.

Periodically some smart writer will get ahold of the fact that stealth aircraft are generally less stealthy at lower frequencies. Then articles will appear claming Stealth has no value, since HF (or VHF, or UHF, or whatever that writer goes with) radars see right through it.

All of this was well understood before the first intentionally reduced radar cross section aircraft flew. Reading a few basics about RCS, RCS reduction, and how RCS calculations break down once you exit the optical region will show anyone at least the basics of why and how this is. Look at predictions for RCS in the Rayleigh region, Mie region, and optical region for further understanding.

At its most basic level, the modern implementation of stealth comes down largely to shape and surface.

Shapes (both gross shapes and fine shapes) are selected to reflect radar energy anywhere but back towards the radar. And this tends to work well across wider frequency ranges, down to the frequency range where pieces / parts of the target become resonant and up to a frequency were smaller features become resonant.

Surface is another problem all together. You can design surface coatings that absorb or conduct, rather than reflect, RF signals. But they tend to do so over very narrow specific frequency ranges. And at a gross level the thickness of this coating is related to its frequency response, so that such coatings tend to be more effective and robust as you go up in frequency.

All of this means that yes, a very good argument can be made that HF OTHRs can indeed see stealthy targets such as the B-2 bomber. This is one reason these radars have become so popular.

But, tracking a target, such as the B-2 or any other military target, is not the same as shooting it. And while you can build very low frequency detection radars, HF, VHF, UHF, etc, these radars are not well suited to actually engaging a target. Tracking and shooting radars, radars that can guide missiles, guns, or other aircraft onto a target, all tend to, for a variety of physics based reasons, be higher in frequency. Frequencies at which stealth techniques are very effective.

T!

So I guess that's why when the B-2 has to drop a load they plan their route very carefully.

 

[AK_SAR]

Some fascinating photos of a Soviet "woodpecker" antenna are at:
https://www.cnn.com/travel/article/duga-radar-chernobyl-ukraine/index.html

 

[VK3RX]

Looks the same one I posted in the earlier link.

 

[poltergeisty]

Some fascinating photos of a Soviet "woodpecker" antenna are at:
https://www.cnn.com/travel/article/duga-radar-chernobyl-ukraine/index.html

I believe the first Call Of Duty Black Ops game featured this.