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Author Topic: Wideband, High-Pulse Radar  (Read 3757 times)

Offline PresentedIn4D

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Wideband, High-Pulse Radar
« on: September 26, 2013, 1827 UTC »
https://dl.dropboxusercontent.com/u/16642779/UNIDradar.wav

Idles for a minute or so, goes into a large 300Hz pulse.

Known frequencies:
9050
7990
7959
6970
« Last Edit: September 26, 2013, 1830 UTC by PresentedIn4D »
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Offline ChrisSmolinski

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Re: Wideband, High-Pulse Radar
« Reply #1 on: September 26, 2013, 1859 UTC »
Here is what it looked like here:

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Re: Wideband, High-Pulse Radar
« Reply #2 on: September 26, 2013, 2240 UTC »
Isn't that the OTH station in New Zealand? ???

Peace!

Offline Token

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Re: Wideband, High-Pulse Radar
« Reply #3 on: September 27, 2013, 0408 UTC »
This signal is one I have been watching since late 2011, in my log it is called “Big Tones”.  Originally it started with 1 kHz tones (pulse repetition rate), and has also used that pulse spacing recently, but most often it uses the 300 Hz as you have shown here.

I cannot tell you what it is (I simply do not know, although I have a few rough guesses) but I can tell you what it is not.  It is almost certainly not a radar, and it is almost as certainly not a sounder.

So, why not a radar?

With any radar you can tell certain potential performance parameters based on the transmitted signal.  This does not give you the complete picture of its capabilities, but it does define a few boundaries of performance.  Depending on the radar type (pulse, FMCW, pulse Doppler, etc) you can tell different things from its transmissions.

With a simple pulse transmission like this one (there does not appear to be any modulation on the pulses that are significant for radar applications) three parameters are very easy to determine.  Maximum possible unambiguous range and minimum range resolution.  Maximum unambiguous range is simply the maximum range at which the radar can detect a target and be sure of the range.  Minimum range resolution is the minimum distance between two targets that is possible and the radar still be able determine that there are two targets there, not just see the two (or more) as a single target.  The same factors that determine minimum range resolution also determine minimum possible detection range, the closest target that can be seen.

Maximum unambiguous range is determined with the formula R = (c x t) / 2.  R is the max range, c is the speed of light, and t is the radar PRI (pulse repetition interval, time between pulses, leading edge to leading edge).  The speed of light and the time need to be in the same time unit, normally seconds.  Whatever distance unit is used for c will determine the distance unit for R.

We will call c = 300000 km/sec.  The PRI for this signal is 3.333 msec, or 0.003333 seconds (this is 300 Hz, as in your example, but I have seen it as high as 303 Hz).

(300000 x 0.003333) / 2 = 499.95 km

So the maximum unambiguous range is 500 km.  OK, this seems a reasonable max usable range for a radar, even if a bit short by some OTHR standards.

Minimum range resolution is determined using the formula Rr = (c x PW) / 2.  Looks familiar, ah?  Radar is very time dependant, and radar wave travel at the speed of light after all.  Rr is the minimum distance apart two targets can be and be detectable as individual targets.  c is as defined above in the maximum range formula.  PW is the pulse width.

The pulse for this signal is 900 microseconds, or 0.0009 seconds (I have seen shorter pulses also, down around 835 microseconds).

(300000 x 0.0009) / 2 = 135 km.

(edit) I originally failed to mention that Pulse Width also determines the minimum range at which a simple pulsed monostatic radar can be used.  It cannot listen while the pulse is being transmitted, and so during this pulse transmission time, and for some recovery time after the pulse ends, the radar is “blind”.  Since time is distance then the minimum range a radar using the above pulse width can see would be a bit over 270 km.

So, if this signal were a radar it would have a maximum usable range of 500 km, a minimum usable range of 270+ km, but it would not be able to tell two targets apart unless they were over 135 km apart.  Basically it would end up with less than 2 usable range cells in its full range.  This means that if there were 2 targets in its illumination cell that were each 130 km from the other then it would see one large target from min range to max range.

Not a very affective design ;)  And the 1 kHz version of the signal is even more limited, since it uses a 50% duty cycle (square wave).  So, in my opinion and based on a few years in the field of radar, almost certainly not a radar.  There are also a couple of other modulations seen on the signal, such as a 4.5 kHz sine wave of low modulation depth.

I have been seeing this signal since late 2011.  It uses several frequencies, and seems to hit them pretty dependably / repeatedly.  It generally starts at the lowest freq and then moves up as time goes on, but it frequently goes back and revisits

Some of the frequencies seen (not a complete list, but the most common ones I have seen, each used at least 3 times on separate dates in my logs):

4040
4810
5385
6400
6970
7595
7990
9050
9803
11065
12045
13530
16060
17048
18036
19270
20510
21460
23180
24450
26875

Video of the signal on 6970 in 2012 (PRF and PW slightly different from your example, but the same signal):
http://www.youtube.com/watch?v=3AIZLc-ZqW0

Picture of the spectrum (if you have no other way to detect the pulse width the reciprocal of the time from peak to first null will yield the PW, or half the frequency from first null on low freq side to first null on high freq side):



Hope some of this helps.

T!
« Last Edit: September 27, 2013, 1341 UTC by Token »
T!
Mojave Desert, California USA

Offline SW-J

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Re: Wideband, High-Pulse Radar
« Reply #4 on: October 15, 2013, 1632 UTC »
This signal is one I have been watching since late 2011, in my log it is called “Big Tones”.  Originally it started with 1 kHz tones (pulse repetition rate), and has also used that pulse spacing recently, but most often it uses the 300 Hz as you have shown here.

I cannot tell you what it is (I simply do not know, although I have a few rough guesses) but I can tell you what it is not.  It is almost certainly not a radar, and it is almost as certainly not a sounder.

So, why not a radar?

With any radar you can tell certain potential performance parameters based on the transmitted signal.  This does not give you the complete picture of its capabilities, but it does define a few boundaries of performance.  Depending on the radar type (pulse, FMCW, pulse Doppler, etc) you can tell different things from its transmissions.

With a simple pulse transmission like this one (there does not appear to be any modulation on the pulses that are significant for radar applications) three parameters are very easy to determine.  Maximum possible unambiguous range and minimum range resolution.  Maximum unambiguous range is simply the maximum range at which the radar can detect a target and be sure of the range.  Minimum range resolution is the minimum distance between two targets that is possible and the radar still be able determine that there are two targets there, not just see the two (or more) as a single target.  The same factors that determine minimum range resolution also determine minimum possible detection range, the closest target that can be seen.

Maximum unambiguous range is determined with the formula R = (c x t) / 2.  R is the max range, c is the speed of light, and t is the radar PRI (pulse repetition interval, time between pulses, leading edge to leading edge).  The speed of light and the time need to be in the same time unit, normally seconds.  Whatever distance unit is used for c will determine the distance unit for R.

We will call c = 300000 km/sec.  The PRI for this signal is 3.333 msec, or 0.003333 seconds (this is 300 Hz, as in your example, but I have seen it as high as 303 Hz).

(300000 x 0.003333) / 2 = 499.95 km

So the maximum unambiguous range is 500 km.  OK, this seems a reasonable max usable range for a radar, even if a bit short by some OTHR standards.

Minimum range resolution is determined using the formula Rr = (c x PW) / 2.  Looks familiar, ah?  Radar is very time dependant, and radar wave travel at the speed of light after all.  Rr is the minimum distance apart two targets can be and be detectable as individual targets.  c is as defined above in the maximum range formula.  PW is the pulse width.

The pulse for this signal is 900 microseconds, or 0.0009 seconds (I have seen shorter pulses also, down around 835 microseconds).

(300000 x 0.0009) / 2 = 135 km.

(edit) I originally failed to mention that Pulse Width also determines the minimum range at which a simple pulsed monostatic radar can be used.  It cannot listen while the pulse is being transmitted, and so during this pulse transmission time, and for some recovery time after the pulse ends, the radar is “blind”.  Since time is distance then the minimum range a radar using the above pulse width can see would be a bit over 270 km.

So, if this signal were a radar it would have a maximum usable range of 500 km, a minimum usable range of 270+ km, but it would not be able to tell two targets apart unless they were over 135 km apart.  Basically it would end up with less than 2 usable range cells in its full range.  This means that if there were 2 targets in its illumination cell that were each 130 km from the other then it would see one large target from min range to max range.

Not a very affective design ;)  And the 1 kHz version of the signal is even more limited, since it uses a 50% duty cycle (square wave).  So, in my opinion and based on a few years in the field of radar, almost certainly not a radar.  There are also a couple of other modulations seen on the signal, such as a 4.5 kHz sine wave of low modulation depth.

I have been seeing this signal since late 2011.  It uses several frequencies, and seems to hit them pretty dependably / repeatedly.  It generally starts at the lowest freq and then moves up as time goes on, but it frequently goes back and revisits

Some of the frequencies seen (not a complete list, but the most common ones I have seen, each used at least 3 times on separate dates in my logs):

4040
4810
5385
6400
6970
7595
7990
9050
9803
11065
12045
13530
16060
17048
18036
19270
20510
21460
23180
24450
26875

Video of the signal on 6970 in 2012 (PRF and PW slightly different from your example, but the same signal):
http://www.youtube.com/watch?v=3AIZLc-ZqW0

Picture of the spectrum (if you have no other way to detect the pulse width the reciprocal of the time from peak to first null will yield the PW, or half the frequency from first null on low freq side to first null on high freq side):



Hope some of this helps.

T!

Good post, and applicable for 'search' modes, but, overlooks ISAR (Inverse synthetic aperture radar) techniques, which allow finer detail to be observed/resolved on targets once something has been detected; by saturating a target with a series of pulses a 'profile' of the target can be detected by observing the minute Doppler shifts imparted on the reflected RF energy ... also using multiple frequencies (in combination with ionospheric sounder data) allows improved target location, allowing some of the vagaries of HF propagation to be 'nulled' out.
 

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Offline Token

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Re: Wideband, High-Pulse Radar
« Reply #5 on: October 15, 2013, 2245 UTC »
Good post, and applicable for 'search' modes, but, overlooks ISAR (Inverse synthetic aperture radar) techniques, which allow finer detail to be observed/resolved on targets once something has been detected; by saturating a target with a series of pulses a 'profile' of the target can be detected by observing the minute Doppler shifts imparted on the reflected RF energy ... also using multiple frequencies (in combination with ionospheric sounder data) allows improved target location, allowing some of the vagaries of HF propagation to be 'nulled' out.
 

I have not done any SAR work myself, so have little first-hand knowledge of the systems used, but I have had some small, mostly academic, exposure to them.  Although SAR, and ISAR, use aperture synthesis, via motion, to improve spatial resolution (cross range) the basic range resolution of the system is still defined by the signal bandwidth.  That is why SAR typically uses very short pulse widths, with bandwidths on the order of 6 MHz or more.  This signal exhibits no chirp or other modulations to increase bandwidth, so for it bandwidth (range resolution) is primarily a function of pulse duration.  Remember I mentioned range resolution as it applies to the ability to discriminate more than one target, not as a factor in accuracy of range determination or to plot motion.

Another issue is the PRF of this “system”.  This PRF is about 300 Hz.  Gough and Hawkins (Jan 1997, IEEE JOE) suggest a SAR aperture motion (target motion, ISAR) per pulse of no more than D/4.  At 300 Hz this means a target motion of no more than 75 m/s, roughly 270 km/h.  OK for ships, but not most tactically important airborne objects.

However, assuming this signal was using some SAR or ISAR technique, every time I have watched this signal it is essentially never up for any length of time, typically less than 2 minutes (pulsed, longer if you include its CW time) per frequency, and often less than 45 minutes total in 8 hours.  It often hits a specific frequency range (and thus illumination cell for given propagation conditions) only once or twice in a 24 hour period.  It simply does not illuminate any target area long enough or often enough to be a usable radar, regardless of other performance limitations.

Yeah, one could play lots of games with unusual processing to say this might be some kind of radar, but as I said before, it is almost certainly not a radar, I will further add, in my opinion.  It is certainly not a radar using common techniques (considering the waveform) applied to skywave HF radar.

I guess the important take-away from my post is that to me it does not feel like a radar, although it could, technicaly, be possible using some obscure (for the application when using such a waveform) techniques.

T!
« Last Edit: October 17, 2013, 1231 UTC by Token »
T!
Mojave Desert, California USA

Offline Token

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Re: Wideband, High-Pulse Radar
« Reply #6 on: October 19, 2013, 2057 UTC »
October 19, 2013, 2054.  In the last hour seven "Big Tones" frequencies have been active with dead carriers.  This is common before the signal (tones) becomes active.  

2035 - 2041 UTC,  17048 kHz carrier
2044 - 2050 UTC,  18036 kHz carrier
2052 - 2058 UTC,  19270 kHz carrier
2059 - 2105 UTC,  20510 kHz carrier
2107 - 2112 UTC,  21460 kHz carrier
2114 - 2119 UTC,  23180 kHz carrier
2122 - 2128 UTC,  24450 kHz carrier

Look towards the freqs I posted in tis thread earlier for more potential activity.

T!

(edit, added 4th, 5th, 6th, 7th  freq seen)
« Last Edit: October 19, 2013, 2128 UTC by Token »
T!
Mojave Desert, California USA

Offline skeezix

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Re: Wideband, High-Pulse Radar
« Reply #7 on: October 19, 2013, 2119 UTC »
Heard the carrier on 23180 at 2118Z.

It went away at 2119Z, but looked like it kinda pathetically died instead of cleanly off. Interestingly, a chirp sounder did its thing shortly after and could see it on the waterfall from 23090 and it stopped at 23180 (waterfall went up to 23210, so I have no idea if it really ended at 23180 or there's just a large gap).

Nothing heard on any of the other listed freqs 2119-2123Z.

2125Z carrier on 24450. Only S5 and has deep fades.
2128Z 24450 carrier faded out.
2135Z carrier on 26875
2142Z 26875 carrier faded out.

« Last Edit: October 19, 2013, 2142 UTC by skeezix »
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Offline Token

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Re: Wideband, High-Pulse Radar
« Reply #8 on: October 19, 2013, 2248 UTC »
Heard the carrier on 23180 at 2118Z.

It went away at 2119Z, but looked like it kinda pathetically died instead of cleanly off. Interestingly, a chirp sounder did its thing shortly after and could see it on the waterfall from 23090 and it stopped at 23180 (waterfall went up to 23210, so I have no idea if it really ended at 23180 or there's just a large gap).

Nothing heard on any of the other listed freqs 2119-2123Z.

2125Z carrier on 24450. Only S5 and has deep fades.
2128Z 24450 carrier faded out.
2135Z carrier on 26875
2142Z 26875 carrier faded out.



The "fade down" is common for this signal when using a carrier like this.  It is like they turn the power down before turning the TX off.  When the signal is strong you can see the TX is turned off after it has been turned down some, so it kind of rolls off before turning off.  If you pay attention during the carrier some of the “fades” were controlled reductions in power, down to similar levels that are seen just before the TX is switched off.

T!
T!
Mojave Desert, California USA

Offline skeezix

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Re: Wideband, High-Pulse Radar
« Reply #9 on: November 03, 2013, 1517 UTC »
For a couple weeks or so, I've been seeing something that seems similar (or the same) to the big tones thing, but its around 17450. Its there now, 3 Nov 2013 1511 UTC. Checked again at 1539 UTC and its gone. Still see the stupid blob and the broadcaster that was there earlier at 17500.

That white blob on the right is RFI and its all over 17 MHz. Haven't been able to find the source yet. There's another blob off to the left of the screenshot.


« Last Edit: November 03, 2013, 1540 UTC by skeezix »
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Re: Wideband, High-Pulse Radar
« Reply #10 on: November 03, 2013, 2218 UTC »
Wow. I paused on this same signal yesterday (11/2) on 17450. I was S T R O N G into ga at that time.

Offline Token

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Re: Wideband, High-Pulse Radar
« Reply #11 on: November 03, 2013, 2349 UTC »
The 17450 kHz signal is a meteor radar called SKiYMET.  You will also see it on 29850 kHz and on a VHF-Lo freq (38.15, 35.25 MHz, plus other possibles).  Both 17450 and 29850 are present pretty much daily.  As the cycle shifts it sometimes goes away from one or the other freq for extended periods, but for the last couple months both have been in daily use.

Video of it here (old video, I need to do a more current one):
http://www.youtube.com/watch?v=WkcxsJiKcvk

T!
« Last Edit: November 04, 2013, 0102 UTC by Token »
T!
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Offline skeezix

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Re: Wideband, High-Pulse Radar
« Reply #12 on: November 04, 2013, 0200 UTC »
Cool, thanks.

There is a lot of interesting things going on HF.
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