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Understanding 90 degree linear crossing in front of F-14 radar. Targets at varying distanse and altitude


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Hello. I've been trying to understand how the radar in the F-14 works in regards to targets crossing in front of me at 90 degrees. The targets are at varying altitudes.

 

I've been testing using a self made mission where I start at 33000 feet flying towards three targets 80nm out at 6000feet, 16000feet and 33000 feet.

 

Finding them head on is no issue, however starting 90 degrees to their left or right will not pick up the targets on the radar. I fly as a pilot and "steer" Jester accordingly, but no luck in getting a targetmarker in the TID. A friend of mine has been flying the same mission as RIO and has no luck in finding the targets either.

 

I have somewhat understanding of the doppler effect and notch-filter but it is limited to whatever DCS-videoes made on the issue.

 

My questions are; What makes the targets not being picked up by the radar when they cross 90-degrees infront of me, and is there a way to work around it to make a better environment for the radar to pick them up withouth flying infront/after them?

 

And; I was under the impression that the notchfilter-effect was only present with a background ie. mountains, but will the notchfilter also make it hard for the radar to pick up targets without any background?

 

Thanks for any replies 🙂

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The reason this occurs is due to how the computer filters out ground clutter, the "notch" filter is called the main lobe clutter filter, and it filters out ground clutter in the main radar lobe. The way it does this is to suppress all of the returns for certain values of closure rate. The values suppressed by the AWG-9 are own aircraft ground speed plus and minus 133kts, for example, if the F-14 is going 400kts across the ground, the radar will suppress returns with a closure rate between 533 and 277kts. this range contains almost all the returns from the ground, which has a closure rate to the F-14 of approximately its ground speed. The aircraft does not know what it is suppressing, so it cant automatically turn this filter off if there is no background, with one exception, if the antenna elevation is +3 degrees from the horizon or greater (note this is different from scan pattern elevation) the main lobe clutter filter is automatically disengaged, and the AWG-9 radar cannot be notched.

 

As a pilot, the only thing you can do to better engage aircraft that are beaming you (flying 90 degrees to your heading) is to reduce your altitude so that the radar is looking up at the target, or change your direction in order to change the targets closure rate. 

 

A human RIO (and maybe jester, I don't remember) can manually disengage the main lobe clutter filter, however this will also stop the suppression of all ground returns, and so the RIO must manually pick out the correct targets from the clutter (a difficult task).

 

EDIT: the main lobe clutter filter is labeled as "MLC Filter" in the back seat 


Edited by Saber2243
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Thank you so much for an excellent reply, Saber!

 

I am still wondering what you are describing in regards to what the radar suppress. I interpret your explaination that the radar isn't "smart enough" to identify whether or not the aircraft beaming me is an aircraft or actually ground clutter, even though there is no background?

 

In this video by "Jabbers" DCS World - Notching Tutorial - YouTube, he explains that beaming the intercepting airplane is not enough to enter the notchfilter. To enter a notching environment you also need a static background to hide in front of.

 

In other words, I interpret the AWG-9 radar is not smart enough to seperate these two issues ie. it doesn't matter if there is a background or not as long as the aircraft is beaming and the MLC-filter is on? Is that correct?

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42 minutes ago, NightstalkerNOR said:

I interpret your explaination that the radar isn't "smart enough" to identify whether or not the aircraft beaming me is an aircraft or actually ground clutter, even though there is no background?

Yes, no radar is (at least, no radar that doesn't do a bunch of extra signal processing). Radar angular resolution without funny imaging techniques is terrible (as in, roughly 4 orders of magnitude worse than e.g. a IR or TV sensor), which is why radar hits are just a blip on a screen rather than a nice, clean, resolved picture like e.g. a TCS track. There really is no way to tell whether something is an aircraft or something else other than "is this thing moving too fast to be anything but a plane", essentially (obviously other radar modes with other radar are different, e.g GMT in the Hornet, but that's the gist of it).

 

42 minutes ago, NightstalkerNOR said:

n this video by "Jabbers" DCS World - Notching Tutorial - YouTube, he explains that beaming the intercepting airplane is not enough to enter the notchfilter. To enter a notching environment you also need a static background to hide in front of.

 

In other words, I interpret the AWG-9 radar is not smart enough to seperate these two issues ie. it doesn't matter if there is a background or not as long as the aircraft is beaming and the MLC-filter is on? Is that correct?

Depends on how you set the MLC switch. To quote the manual, "The MLC switch controls how the system supresses the MLC in the radar system while in pulse doppler mode. The OUT position disables the system while the IN position enables it. The AUTO position automatically enables the MLC filter if the antenna look-up angle is less than 3°". So basically if the MLC is in AUTO, and you're in a look up situation (ie, lower altitude than your target, so that there is no background they can hide in), they can try to notch all they want and the AWG-9 will still pick them up.

 

Also what Saber forgot to mention is that there's a second radar blind spot. Again to quote the manual,

"The second filter, and second blind spot, of the radar is the zero doppler filter. This blind area is centered around a closure rate of negative own groundspeed, meaning a target moving away from own aircraft at the same speed as own aircraft. This blind area is a hardware limitation as it is a doppler radar mode it cannot detect targets without a doppler shift. The resulting blind area is 200 knots wide, meaning that a chased target moving at a speed of within 100 knots (+/-) of own groundspeed will be invisible to the radar. This means that when chasing a fleeing target it may very well be necessary to use the pulse modes instead."

 

Unlike the MLC switch, this mode can not be deactivated. To continue on the previous case (look up target trying to avoid eating a missile fired from the Tomcat), they do have the option of turning tail completely and running away at, say, 400/500 knots or something, expecting the Tomcat to fly at a similar speed. In that case, the AWG-9 won't be able to pick up the target. Obviously in this case, said target is also not a danger to anyone in the Tomcat or its vicinity.


Edited by TLTeo
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1 hour ago, TLTeo said:

 

Unlike the MLC switch, this mode can not be deactivated. To continue on the previous case (look up target trying to avoid eating a missile fired from the Tomcat), they do have the option of turning tail completely and running away at, say, 400/500 knots or something, expecting the Tomcat to fly at a similar speed. In that case, the AWG-9 won't be able to pick up the target. Obviously in this case, said target is also not a danger to anyone in the Tomcat or its vicinity.

 


I knew as soon as I omitted it that someone was going to bring up the zero doppler filter.
Just to add on, the options you have for countering a target exploiting the zero doppler filter are:
Change own ground speed to increase closure or separation to more than 100kts 

Change aircraft direction to increase closure or separation to more than 100kts 

utilize a pulse mode, PAL, PLM, and VSL HI/LO are all pulse STT modes, the RIO can also put the target into a pulse STT, in these modes obviously you will be unable to fire a AIM-54 in TWS or FOX-1 mode, but you can fire it active off the rails

 

EDIT: Also I am fairly certain the manual is wrong about the reason for the zero doppler filter, I am fairly sure it is to suppress side lobe clutter returns from directly below the aircraft


Edited by Saber2243
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6 hours ago, Saber2243 said:

utilize a pulse mode, PAL, PLM, and VSL HI/LO are all pulse STT modes

Just to correct - these are search/acqusition modes that can lead to STT lock when successful. STT can be either pulse or pulse-doppler. :thumbup:

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9 hours ago, draconus said:

Just to correct - these are search/acqusition modes that can lead to STT lock when successful. STT can be either pulse or pulse-doppler. :thumbup:

While STT can be either, these modes will always produce a Pulse STT, only the RIO can drop directly into PD-STT, of course the RIO can also change the mode once the lock is acquired, but when using these modes, the initial lock will be pulse

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You might find this useful. 
 


Edited by Spiceman

Former USN Avionics Tech

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