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majoco

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Well, it's about 60miles east of Bangor, Maine where my partner's neice lives, according to your co-ordinates. Probably some old OTHR or something to do with the obsolete Dew Line system seeing as its about as far to the North East as you can get on mainland USA.
 

ecps92

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Originally thought it could be Cutler but then double checked on the map. :(

Google Earth has a placemark for OTHR [Over the Horizon Radar] with two photos.

Also see http://en.wikipedia.org/wiki/Columbia_Falls_Air_Force_Station



Well, it's about 60miles east of Bangor, Maine where my partner's neice lives, according to your co-ordinates. Probably some old OTHR or something to do with the obsolete Dew Line system seeing as its about as far to the North East as you can get on mainland USA.
 
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Token

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Yes, this is the AN/FPS-118 OTH-B. The FPS-118 was a bistatic system, and these images are of the receive site. The transmitter site was located at a seperate base, about 100 miles away to the east.

Although I never worked on this system myself one of my jobs in the 70's (working at the Verona Test site at the time) was with several engineers who were involved in this effort at the RADC.

T!
 
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k9rzz

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So, with all the hullabaloo over the Soviet's Woodpecker during the cold war, why no complaints about this megawatt monster in our own backyard?

Token?
 

zl2taw

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So, with all the hullabaloo over the Soviet's Woodpecker during the cold war, why no complaints about this megawatt monster in our own backyard?

Token?
It was easier to blame the Soviets, even in NZ we blamed the russian woodpecker for everything
 

lep

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The US version didn't put crud all over the ham bands, the Russians did that.
 

Rick1959

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Some information I found on the web, for more detailed information I provided a link.

"The prototype was built in Maine, with the transmitter at Moscow Air Force Station [45°08'14"N 69°48'07W] and the receiver at Columbia Air Force Station [44°47'42"N 67°48'41"W]. Experimental transmissions from the Maine site covered an arc from 16.5° to 76.5° and from 900 to 3,300 km in range. Initial testing was conducted from June 1980 to June 1981. GE Aerospace (now Lockheed Martin Ocean, Radar and Sensor Systems) in received a contract in mid-1982 for full-scale development of the program."

"The Air Force maintains the six East Coast and West Coast OTH-B radars in a state called "warm storage," which preserves the physical and electrical integrity of the system and permits recall, should a need arise. It would require at least 24 months to bring these first generation OTH-B radars out of caretaker status and into an operational status-if such a decision to do so were made. Major upgrades costing millions of dollars would be necessary to bring the outdated technologies up to modern standards. The incremental cost of operating the East Coast OTH-B system for environmental research and services is about $1.0M to $1.5M per year. The environmental monitoring aspects of the system are unclassified. Similar coverage in the eastern Pacific could be obtained at about the same cost."

AN/FPS-118 Over-The-Horizon-Backscatter (OTH-B) Radar - United States Nuclear Forces
 

E-Man

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Thanks for the additional info Rick, very interesting.
 

Token

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As far as complaints about the Russian Woodpecker vs US/other nations OTHRS, I have got to agree with lep for the most part. Opinion only here, I have no hard documentation, mostly my memory and some assumptions based on known aspects of the technology and operations.

The Russian Woodpecker did its thing pretty much anyplace and everyplace it wanted, including ham and broadcast bands. Also, it was a simple pulse type transmission (sharp rise and fall times and relatively narrow pulse widths mean wide band noise) that ran for sometimes hours at a time on a frequency. The US versions most often stayed away from ham and broadcast bands. Systems like the FPS-118 were/are mostly LFMCW and so they are actually often more narrow banded from a noise aspect. They also tend to shift frequency more often to get some enhancement, so they set on a given frequency for less annoying time. One other aspect that might have contributed, at least as far as US observations were concerned, was the fact that the Woodpecker (at least one of them) was pointed in the general direction of the US, while US OTHRs were most often pointed out and away.

T!
 
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Token

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So, with all the hullabaloo over the Soviet's Woodpecker during the cold war, why no complaints about this megawatt monster in our own backyard?

Token?

Revisit. I’ll tell you right now, this might be a little long winded. Why was the Russian Woodpecker so hated, vilified, abased, and general known to be a no-goodnik when other similar power level OTHRs existed at the same time and were hardly noticed?

I gave my guess earlier, the Woodpecker used a different transmission waveform from the majority of others (HF radars) in use then and especially today, a waveform that was much more noticed or intrusive, and the Woodpecker made no real attempt that I could tell to stay away from ham and SW BC bands.

Why the revisit? Thursday at work I was running a new, fresh out of school, engineer through some basics of one of our radar systems. Making sure he understood the specifics of the dynamic range, MDS, filter bandwidths, integration gain, Doppler bin size and affects on performance, etc, etc of that system and at the same time getting him some hands on the hardware. As we wrapped up I realized I already had the test equipment out and set up to build a basic simulation of the Woodpecker OTH waveform….and I had one of my SDRs on my desk.

The simulation is not perfect. The real Woodpecker had multiple modes of operation, but apparently the most common was a 3.1 msec pulse and a 90 msec pulse repetition interval. This was easy to set up. But apparently the real Woodpecker also used a pulse compression technique that divided the 3.1 msec into a series of 31 sub pulses, each 100 microsec long. Unfortunately I could find no details on the specifics of this, so I just left it out of the simulation instead of guessing wrong. The affect will be that my Woodpecker simulation is LESS intrusive, and more narrow banded, than the original.

For comparison I also did a simulation of an LFMCW (Linear Frequency Modulated Continuous Wave) type waveform, as might be seen from the FPS-118 or similar radars and on many sounders. The simulation is NOT of any specific radar or sounder, just a generic 20 kHz wide, 20 Hz rate, LFMCW signal. Some systems are wider than this, some more narrow, some with a faster rate, some slower.

A few pictures.

This first image is of the pulse used in the simulation, 3100 microsec. I did not embed the image as it is not very important but here is the link if you want to see it.
http://www.pbase.com/token/image/140207461/original.jpg

The second and third images are fine detail of the spectrum of the pulse. The symmetry and deep nulls indicate the pulse is fairly clean, with good rise and fall times. Having not seen a pulse image of the Woodpecker (I never thought to look at it that closely when it was active) I do not know how this compares, but I know the Russians were and are pretty good at high power pulsed stuff, no reason to suspect they would not have a good pulse. The bandwidth of the first spectrum here is only 2 kHz wide, but it was needed to show detail, the displayed bandwidth in the second image in this set is 10 kHz. Again, I did not embed these images, but here are the links if you want to see them.
http://www.pbase.com/token/image/140207462/original.jpg
http://www.pbase.com/token/image/140207463/original.jpg


The fourth image gets to the heart of the matter, what does the pulsed signal look like at wider bandwidths? In this case the spectrum shown is 190 kHz wide, and you can see the signal is still seen at the far edges, so that despite the fact the signal is centered on 10000 kHz it is covering at least 9905 to 10095. In fact, it is wider than that, but the SDR-IQ I had with me only shows 190 kHz width maximum. Also keep in mind this is an S9 level signal simulation, it was common for the Woodpecker to be much higher than this, 20 over S9 was common at my location, so in that case the signal at the edges of this image would be 20 dB higher. We see –105 dBm in this image, so the power 95 kHz off of center freq would have often been –85 dBm or higher, and that power level is S6 on a calibrated S meter. And remember I did not include the pulse compression technique that would have made it even worse away from the center frequency.


The fifth image is the comparison to an LFMCW waveform. The total displayed bandwidth is 50 kHz in the picture. You can see there is a little power outside the specific 20 kHz swept, and 10 kHz either side of the signal is right down to the system noise floor. So worst case this signal might be heard on a receiver for maybe 40 kHz of tuned width, and probably more like 30 kHz or less.


Pictures are all well and good, but what does this mean to the ear and when operating a receiver? So, a couple of videos to show the affects.

The first video is the simulated Woodpecker as received in AM mode. The video starts tuned on center frequency and with the display 20 kHz wide. I then widen the display to 190 kHz width to show more of the signal, and tune away from center frequency in 10 kHz steps. I tune up to 10090 kHz and down to 9910 kHz and the signal is still clearly heard. And keep in mind this power level is only moderate, not the needle bending signal sometimes seen with the real system.
Russian Woodpecker simulation, 3.1 msec pulse, 90 msec PRI, 10000 kHz cf, 190 kHz bandwidth - YouTube

The second video is of the generic 20 kHz wide LFMCW simulation received in USB mode, USB was selected for this video as simple AM mode does not show this type of signal as well as it does the Woodpecker. The video starts tuned to center frequency and the display is 40 kHz wide. I then widen the display out to 190 kHz and again tune away from center freq in 10 kHz steps. I tune up to 10080 kHz and down to 9910 kHz. It is apparent the signal from the LFMCW is no longer heard once you are tuned away more than 5 or 10 kHz from the swept frequency edge. That means you can hear this signal for about 30 kHz or just a little more of width.
Generic LFMCW HF radar simulation, 20 kHz sweep width, 20 Hz rate, 10000 kHz cf, 190 kHz width - YouTube

When you combine all of the above with a system who’s operating habits did not avoid ham and SW BC bands I think it becomes pretty clear why the Woodpecker was perceived as such a pain in the butt. And yeah, it was easy to blame also.

And a last video, for anyone who is not aware of what an LFMCW radar is doing. It really has nothing to do with the above stuff, why radars using a waveform like the Woodpecker were such a pain compared to other waveforms. In this video I start an LFMCW at a 1 Hz rate, and this you can see with your eyes, it starts at a low freq and sweeps up linearly for its entire swept band. Then it jumps from the highest frequency back down to the lowest, starting the cycle all over again. This one sweeps up, or low to high, but some might sweep down, high to low, instead. In this case I have used a sawtooth, as that is most common. As the video progresses I step the sweep rate up, from 1 Hz, to 2 Hz, to 5, 10, 20, 50, 100, 500, and 1000 Hz. The width remains the same, only how often in one second the sweep occurs is changed (and this then also changes the chirp rate). Many HF OTHRs use 20, 40, and 50 Hz sweep rates, but anything might be used depending on the operational parameters of the systems, what kind of targets it is looking for and what the anticipated speed range of targets might be.
Generic LFMCW HF radar simulation, multiple sweep rates, 1 to 1000 Hz, 50 kHz displayed bandwidth - YouTube

There are other types of modulation used by HF radars, some similar to these such as the LFMICW (note the extra “I” in the descriptor, it stands for Interrupted, meaning they just break the sweep up a little bit) used by CODARS, and the simple pulse of the SuperDARN / HF TIGER systems, others very different.

T!
 
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E-Man

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Cool reproduction of the Woodpecker, glad it is no longer in service.
 
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