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Old 03-03-2020, 03:45 PM   #991
Harlikwin
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I think you guys may have hashed this out, or at least there is a MIT Lincoln lab video/webpage that explains the difference.

My understanding is that MTI techniques won't provide velocity vector information, just that "its there and moving".
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Old 03-03-2020, 07:46 PM   #992
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Beamscanner, we already had here discussion about this. Russian specialists from "Fazothron" ( radar creator ) called RP-23 a "pulse doppler with external coherency" and they considered this device as a "pulse doppler". Believe me or not but they don't care what was said by some dude from USA, so please give a break.... .
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Old 03-03-2020, 08:58 PM   #993
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There is a whole long thread on the secret projects site on this radar.
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Old 03-10-2020, 12:56 PM   #994
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Quote:
Originally Posted by Harlikwin View Post
There is a whole long thread on the secret projects site on this radar.
IIRC the result was that at the time Russian technical literature criticized the American idea, and the main difference really was that West just called something with other terms, so that West really didn't get what Soviets did.

This in that "coherent" vs "non-coherent" terminology that West uses.
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Old 03-25-2020, 12:53 AM   #995
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Just so people who may be completely lost can get caught up I just pulled some definitions from some sources on radars I have.

"MTI"
This is a method of clutter rejection that a radar may employ. Clutter is essentially 'noise' on the scope, think the F14's radar in pulse mode when looking at the ground, that can obscure a target. There are two types of MTI that have been developed. Coherent and non-coherent. The non-coherent is the oldest type and may also be called "area' MTI.
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Non-coherent MTI radars do not process Doppler frequencies. The returns from one scan are subtracted from returns from the next scan. All targets that move at least one resolution cell in the time between scans are displayed. All stationary objects, including fixed clutter, are cancelled and not displayed. In this type of MTI, clutter cancellation is based on the size and movement of the return. Due to changes in the clutter cross section, instabilities in radar operations, variations such as rain or clouds, and noise from the transmitter, clutter cancellation is never complete. In another form of non-coherent MTI, the radar returns from moving targets are compared to the returns from fixed targets, and the fixed targets are cancelled. These non-coherent MTIs are simple, but they do not provide the clutter rejection available from coherent MTI radars.
Next is Coherent MTI.
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A coherent MTI uses the fact that Doppler shifts appear to a pulse radar as phase shifts on the received target pulse. Coherent MTI uses sophisticated circuitry, including stable local oscillators (STALOs) and coherent local oscillators (COHOs) to capture and process these phase shifts. Further processing of these phase shifts yields velocities for each return. Those velocities associated with stationary targets are rejected and only moving targets are displayed. Coherent MTls have a major problem called “blind speeds.” Blind speeds occur for all target Doppler frequencies that are the exact PRF, or any multiple of the PRF, of the radar signal. When a target is moving at a velocity that produces this Doppler frequency, its return is cancelled along with fixed returns.
Now a coherent MTI differs from a Pulse Doppler radar in that
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MTI uses Doppler frequency shifts only to reject clutter while a pulse Doppler radar uses Doppler frequency shifts to reject clutter and to track targets in velocity
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Secret projects site conclusions, pulled together from multiple posts with grammar adjusted so it makes a bit more sense.

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The Saphir-23MLA (N-003E) radar the primary radar in the MIG-23MLA and is defined in Russian literature as a “coherent pulse Doppler radar” with a inverse Cassegrain antenna. In the west this would better be described as a pulse radar with a clutter-referenced MTI mode. It uses "a method of moving target selection by external coherence", which is best described as clutter-referenced MTI rather than non-coherent MTI. A true coherent pulse doppler radar produces identical trains of pulses, allowing you to process doppler information in the phase/frequency that the pulse was given by you. A Coherent-On-Recieve radar transmits varying pulses, but stores the information on the pulse so that on receiving the returning pulse it can be compared to the original transmitted pulse. In contrast Sapfir-23 doesn't store the transmitted pulse information. Instead, it uses the clutter return as a reference signal. So "coherence", by the western definition - in order for the pulse phase to be an integer number of wavelengths apart- it means that the pulses are simply on/off interruptions of a continuous wave. Hence Western "coherence" = Russian "quazicontinuous", rather than Russian "coherence". "quasicontinuous wave" consists of pulses with high repetition frequency. So, at some aspect you can say the wave appears as a continuous but in real it is not, thus the word "quasi=nearly"continuous or in russian (Квазинепрерывный режим излучения-KNI). The Sapfir radar is thus quasicontinuous wave, a pulse radar with high repetition frequency, which at last enabled them to utilize various doppler filtering techniques.

The Sapfir-23 is a pulse radar that uses doppler processing, and uses an external method of obtaining coherence. Hence, you could, at a stretch, say it is a "coherent pulse doppler" radar without lying. The Sapfir-23 was continuously developed, later versions used greater numbers of doppler filters for better range accuracy and introduced additional modes to pick out targets in different situations. Later versions are better in lookdown, but still not comparable to a true pulse-doppler radar. The N-019 is a pulse-doppler radar with true internal coherence, and hence is an interrupted continuous wave ("quazicontinuous") radar.

I will speak about the radars delivered with the Mig-23 variants to Iraq (Mig-23MS, MF, and ML). The radar delivered with the Mig-23MS was the Almaz-23 which was the same delivered with the mig-21bis. That radar was good for nothing; just to summarize. The radar delivered with the Mig-23MF was a Sapfir-23E but interestingly had no capability to launch the R-13M or the R-60. This is an interesting point since the radar mentioned in the second reply by overscan, does have the capability to launch the am weapons. The radar supplied with the Mig-23ML was the Sapfir-23M and not the NOO3. Again it had no capability to launch the R-13M. The technical documentation of the Sapfir-23E was very meager; the main technical documentation was for the Sapfir-23M radar. Here the PRF is 1 KHz and 5 KHz. The quasi-continuous frequency is 100 KHz; it is used only in guiding the R-23R and R-24R Semi Active Radar Homing Missiles. The difference between the western approach and the eastern approach is that the western (not always; the French didn’t adopt this approach in the Matra Super-530 missile) approach use a pure carrier while the eastern approach was to use high repetition pulse. The Soviets never used the western solution for guidance; in fact they criticize it in their scientific literature.

Last edited by nighthawk2174; 03-25-2020 at 01:03 AM.
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Old 03-25-2020, 06:59 AM   #996
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Quote:
The radar delivered with the Mig-23MF was a Sapfir-23E but interestingly had no capability to launch the R-13M or the R-60. This is an interesting point since the radar mentioned in the second reply by overscan, does have the capability to launch the am weapons. The radar supplied with the Mig-23ML was the Sapfir-23M and not the NOO3. Again it had no capability to launch the R-13M.
Not sure what they are talking about here. R-60 and R-13 are IR guided. All the radar has to do is provide ranging information. Unless it is about slaving the IR seeker head to the radar contact?

Last edited by Dehuman; 03-28-2020 at 04:18 AM.
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Old 03-28-2020, 03:59 AM   #997
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If you know anything about radar theory, you'll know that a low PRF waveform is highly ambiguous in doppler.

hence why true pulse doppler radars use high or medium PRFs.


now go ask your SME what PRF it used.
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