AWG9 over land question

[Harlikwin]

So, ive read various sources that say the AWG9 was bad over land. Can anyone specifically explain to me why this should be given that its a pulse doppler radar?

 

@beamscanner

Edited November 16, 2019 by Harlikwin

[r4y30n]

I think it has more to do with max range. Land will scatter the pulses vs a smooth ocean reflecting them further out.

[Harlikwin]

Man, really no answers on this?

 

@beamscanner

[Spiceman]

I don’t know that the AWG-9 was bad over land. It will certainly be better over water as any radar will be. Much less reflection over water as the reflections mostly keep radiating forward like skipping a stone on a lake. Pulse targets are infinitely easier to find, and the MLC filter can be turned off with less detrimental effects making it almost impossible to notch.

[Harlikwin]

Well the hearasay from various AF and nato pilots was that the AWG9 was overhyped. And various f14 guys said it wasnt great over land. What i have heard offered up is that since it was an over water radar it had trouble filtering out ground clutter. I understand that the returns are different, but i dont know that much about how filters or signal processing of that generation of radar worked. So i guess its possible that its right, id just like to know more.

 

I also put those statements at odds with the fact the IRAF got ple ty of AA kills with that radar, presumably many of them over land.

[KlarSnow]

Compared to the APG-63 series of radars and how much easier they were to use, and the fact that they have MPRF all equates to those radars are going to have a much cleaner/easier to read display, hold locks better and require much less effort on the part of the aircrew to employ.

 

So did it suck over land vs over water?

 

It has a lot of power, and many features that CAN make it capable in the right hands, however the more modern radars in f-15s in particular are going to result in a faster, better picture, and a quicker and more stable lock at range in just about any circumstance compared to the AWG-9. May not have as long range a raw detection, but that trade off in reliability and ease of use was probly worth it (as every other modern US A/A radar has been based off the APG-63 family since).

 

Keep in mind the AWG-9 is really a 1950/60s radar molded into a 1970s jet. It’s origins and core go back a long ways and it’s technology was outdated within a few years of being in service. But it was what they had, and it did the job of supporting the Phoenix quite well.

 

Compared to the Phantom radars it was replacing it was light years ahead, compared to the APG-63 series of radars that came out a few years later, it was rather antiquated.

Edited November 17, 2019 by KlarSnow

[near_blind]

Gain Control: The AWG-9s wasn't great, especially compared to radars that would arrive later in the decade.

[Chuck_Henry]

Being a pulse-Doppler radar, the AWG-9 was far better than older "pulse radars" such as those on (most) F-4s and F-5s. “Look-down, shoot-down" capability was a game-changer. It was, however, a mostly analog system. You needed the RIO to perform tasks that are largely automated in the radars of the F-16 and F/A-18, for example.

 

Under the hood, the AWG-9 utilized an analog computer. It wasn't until the F-14D and its APG-71 (the AWG-9 with improvements from the F-15E’s APG-70) that the Tomcat had a digital computer for better processing speed, mode flexibility, clutter rejection, and detection range. It was improved clutter rejection that really made the F-14 a better over-land performer.

Edited November 17, 2019 by Chuck_Henry
Wordiness

[Harlikwin]

So how did the anlalog computer do the doppler filtering. FFTs like modern radars? Or some other method?

[drPhibes]

So how did the anlalog computer do the doppler filtering. FFTs like modern radars? Or some other method?

 

 

A bank of analog bandpass filters.

[Kev2go]

Besides what Klarsnow said (which imo is overall the best answer)

 

il also throw in that various sources also state MPRF is also superior for all aspect detection and tracking. AWG9 as i have read is also not as good as the AN/APG63 in detecting targets in the sides and rear aspects.

 

True in AWG9 Pulse Mode you have all around better all aspect performance in the tomcat relative to other radar modes, but as we know without the Doppler filters the basic pulse mode it will be very prone to ground clutter reflections. In that mode you may as well have flying with a larger F4E radar.

Edited November 18, 2019 by Kev2go

[Harlikwin]

A bank of analog bandpass filters.

 

Can you point me to how that works? It can have math and suff in it :). How are those filters geting time domain info from the freq shift without fft?

[Sealpup]

Can you point me to how that works? It can have math and suff in it :). How are those filters geting time domain info from the freq shift without fft?

 

First off, it isn't a band-pass filter, it's a band-reject filter. Also called a 'notch' filter (hence the term). There would be two notch filters: One set to exactly the radar frequency, and one varied based on the aircaft's calculated ground-speed. The former is used for sidelobe clutter and self-noise filtering, and is always on. The latter would be used for main-lobe clutter rejection. The idea is that the doppler shift would need to be enough to cause the return's frequency to be outside the notch filters' range in order to make it to the signal processor.

[Harlikwin]

First off, it isn't a band-pass filter, it's a band-reject filter. Also called a 'notch' filter (hence the term). There would be two notch filters: One set to exactly the radar frequency, and one varied based on the aircaft's calculated ground-speed. The former is used for sidelobe clutter and self-noise filtering, and is always on. The latter would be used for main-lobe clutter rejection. The idea is that the doppler shift would need to be enough to cause the return's frequency to be outside the notch filters' range in order to make it to the signal processor.

 

How would vary the filter freq based on aircraft velocity? I mean the velocity could be anywhere from 150-900kts.

[r4y30n]

The MLC filter frequency is simply ground speed from the INS fed into this:

 

I assume the bandwidth of +/-133 kts of own speed is to compensate for the limited accuracy of the INS.

[Harlikwin]

I guess i was asking how you geta a analog variable freq filter.

[TLTeo]

Variable capacitors and resistors I imagine? At its very core one does not need a complex circuit to get something like that

[r4y30n]

Take an analog parametric EQ and swap the frequency potentiometer for a transistor driven by the doppler frequency solver.

[BlackPixxel]

Or, as previously written, have a bank of notch filters. Then you basically get the same as when doing a DFT. Each of the filter will be a frequency bin and the output of the filter still has amplitude and phase information.

[Banzaiib]

I have a hunch that most of the AF guys were talking about the lack of medium PRF in the AWG-9 system, which can really improve performance over land and against retreating bandits. (as stated by Kev above)

[Harlikwin]

I have a hunch that most of the AF guys were talking about the lack of medium PRF in the AWG-9 system, which can really improve performance over land and against retreating bandits. (as stated by Kev above)

 

Did the APG-63 in the F15A have that. I've also read the original (pre-PSP) APG-63 was not great either.

[Harlikwin]

I have a hunch that most of the AF guys were talking about the lack of medium PRF in the AWG-9 system, which can really improve performance over land and against retreating bandits. (as stated by Kev above)

 

Any technical reason it couldn't generate a medium PRF?

[KlarSnow]

Apg-63 had mprf/ hprf from the start, I’m no expert on why the awg-9 couldn’t do MPRF, but considering they never upgraded the AWG-9 to do that over its 40 years of use, and its a fairly significant limfac, it was probly not possible without completely rebuilding the radar (like they did with the APG-71).

 

The APG-63 had its own teething issues, as new technology, just like everything else, but it was still a massive leap forwards in use ability and capability over what previous radars provided.

[Harlikwin]

Apg-63 had mprf/ hprf from the start, I’m no expert on why the awg-9 couldn’t do MPRF, but considering they never upgraded the AWG-9 to do that over its 40 years of use, and its a fairly significant limfac, it was probly not possible without completely rebuilding the radar (like they did with the APG-71).

 

The APG-63 had its own teething issues, as new technology, just like everything else, but it was still a massive leap forwards in use ability and capability over what previous radars provided.

 

Well, I think really the issue was that during the cold war which was the bulk of the service life of the 14, it worked over water, so overland performance wasn't exactly a huge priority. And by the time they did get around to upgrading in the 90's they had the -71.

 

I'm just looking for the actual technical reasons/explanations for the comments I've read about its overland performance.

 

I also find it interesting that the Iranians shot down plenty of Iraqi jets with the AWG-9 mostly over land (~62 or so) with a fair number of those being AIM-54 kills, so I'm also wondering if its an overstated problem, or if the iranians somehow modified their sets.

[KlarSnow]

Just because it is harder to use or difficult does not mean ineffective. What you also have to look into in those kills (which would be very hard to find any kind of reliable details) is what were their targets doing, most of the ones I've seen relate to the targets flying straight and level at a relatively high altitude. The tactics we employ in DCS/modern tactics were barely starting to be a thing in the early 80's (cranking/notching) in western airforces. Also who knows if and how well the iraqi RWR's were working, and whether or not they told them anything about the phoenix/awg-9 combo.

 

Essentially there are lots of variables that go into those kills beyond pure radar performance, so I wouldnt take it to mean anything in particular other than it can be effective if employed properly. Just like the Phantoms radar could be very effective if employed properly.