Jabbers - DCS World - F-14 Tomcat - Back Seat - RIO AWG-9 Tutorial

I have edited my post to qualify that I was talking specifically about contacts on the beam :)

 

Ahh yes, that makes a lot more sense. :thumbup:

Ok i think I get it now and Naquaii's explanation now makes sense. Thanks for the great clarification Nikodemuz!

I'm not really sure I follow why would the co-speed target be filtered out by the MLC-filter.

I'd expect it to be a high-PRF mode limitation as IIRC the AWG-9 lacks a medium-PRF mode (which is normally used against receding targets).

I'm not really sure I follow why would the co-speed target be filtered out by the MLC-filter.

 

I'd expect it to be a high-PRF mode limitation, rather than filtering as IIRC the AWG-9 lacks a medium-PRF mode (which is normally used against receding targets).

From the way I understand it now, from the above explanations it's NOT being filtered out by the MLC filter, but it is rather a limitation of the design of the AWG9 it seems the radar is simply not modern enough to compensate (or calculate) for it's own doppler shift which is why the relative 0 speed targets are dropped in this mode of operation. (Again, it's not receeding targets, but targets with a zero relative airspeed to the radar)

From the way I understand it now, from the above explanations it's NOT being filtered out by the MLC filter, but it is rather a limitation of the design of the AWG9 it seems the radar is simply not modern enough to compensate (or calculate) for it's own doppler shift which is why the relative 0 speed targets are dropped in this mode of operation.

Yeah, but you just took that explanation for granted, but the airplane still moves compared to the ground and thus which ground would appear as having zero relative velocity to the receiver then?

It's not only relative zero speed, but like a hundred knots under and over that (it's mentioned and shown in the video, don't remember the exact values anymore).

There might be some ground clutter from slightly in front of the airplane that fits the criteria, but is such extreme side-lobe clutter really that significant?

Since the AWG-9 lacks medium PRF mode and thus uses only high-PRF mode for which the tracking of the receding targets is its known weakness, I'd rather put my eggs in that basket.

Of course, I'm no radar expert, so I could be wrong, but I've only seen mention of AWG-9 side-lobe clutter mentioned mainly as a problem in countering ECM (hence the AN/APG-71 program).

Yeah, but you just took that explanation for granted, without understanding what that means. The airplane still moves and thus which ground would appear as having zero relative velocity to the receiver then?

.

No I didn't, I actually understood the explanation as best I can. (Thanks to Nikodemuz's great clarification :thumbup:). We're not talking about ground returns here, which do indeed have a doppler shift, and are filtered out as well as the radial velocity contacts which have the same doppler shift, we are talking about the so-called 0 relative airspeed doppler filter. It's apparently a real thing and in Naquii's last post he explains why these co-speed tail chase returns are dropped.

No I didn't, I actually understood the explanation as best I can. (Thanks to Nikodemuz's great clarification :thumbup:). We're not talking about ground returns here, which do indeed have a doppler shift, and are filtered out as well as the radial velocity contacts which have the same doppler shift, we are talking about the so-called 0 relative airspeed doppler filter. It's apparently a real thing and in Naquii's last post he explains why these co-speed tail chase returns are dropped.

Nikodemuz only said that the doppler sum would be zero for co-speed targets, but didn't say that these are dropped since the ground still has a relative velocity to the airplane. Besides, from the video you can clearly see that there's a significant range around the co-speed that is filtered out, not just the co-speed value and these would not have a zero sum, so the zero doppler sum is not the issue here.

Naquii mentioned that it's due to the side-lobe ground clutter (which would be somewhere slightly in front of the aircraft and that would explain having to have a range of speeds cut). But, if that's really that significant for the AWG-9 and this co-speed blind-spot implementation is related to that, then the question is if the high-PRF issues with tracking receding targets are simulated at all?

Later radars added medium-PRF (and interleaved) modes so they have an alternative in these pursuit cases.

If anyone is interested, this is a scan from an old textbook on radar systems: https://apps.dtic.mil/dtic/tr/fulltext/u2/a130537.pdf

The information relevant to this discussion is in section 2.12.1 through 2.13.6. It does a great job of explaining the limitations of a pulse-doppler system.

Naquii mentioned that it's due to the side-lobe ground clutter (which would be somewhere slightly in front of the aircraft and that would explain the range of speeds cut).

He also mentioned that it's due to the inability of the radar to take into account it's own doppler shift. THIS is what I took from Nikodemuz's explanation to be the most relelevant problem here. In effect this introduces an error where the radar suddenly can't "see" the target anymore.

As a picture is worth a thousand words, this is my understanding of the 2 filters (taken from a130537)

Co-speed targets are lost (hidden/filtered) in the altitude return.

Beaming targets are lost (hidden/filtered) in the main lobe ground return.

As a picture is worth a thousand words, this is my understanding of the 2 filters (taken from a130537)

 

Co-speed targets are lost (hidden/filtered) in the altitude return.

 

Beaming targets are lost (hidden/filtered) in the main lobe ground return.

Good illustration, thanks. Now I know how this clutter closely in front of the airplane is called, but apparently it's quite strong, as well. I stand corrected.

But, looking at the image, it shows the altitude return blind spot area to be much more narrow than the main lobe clutter. And Jabbers illustrated in the video that the speeds in the range of 100 knots above and below the airplane speed would be filtered out, which is almost as much as the MLC filter range, no?

And a further question would be if any of the high-PRF issues are simulated then?

But, looking at the image, it shows the altitude return blind spot area to be much more narrow than the main lobe clutter. And Jabbers illustrated in the video that the speeds in the range of 100 knots above and below the airplane speed would be filtered out, which is almost as much as the MLC filter range, no??

It is important to remember that these ranges depend on the way the radar is programmed. The graph doesn't show any specific values, only variables. This is because the variables may change depending on what the radar's computer is told to filter out. It is a general illustration, and not specific to the AWG-9. The filter designed to remove altitude and MLC clutter respectively may cover ranges of frequency that differ from radar to radar.

Yeah, good point. I guess they got the info from one of the SME's.

Still, it would be nice to hear if some of the them had anything to say on the radar behavior in regards to being only high PRF capable and the resulting issues. As I've read on the net that the radar was supposedly not at its best tracking receding targets due to it.

You guys have it down pretty much.

One way of looking at it is that both filters filter out unwanted ground returns, the zero dopple filter filtering out the altitude returns, i.e. the sidelobe/sideband returns from the ground directly beneath the aircraft and the MLC filter the ground returns in the main radar lobe.

As the altitude returns come from straight down it forces the radar to have a zero doppler filter as these returns have around 0 doppler.

The MLC filter on the other hand will move with own aircraft speed as your own airspeed varies making the returned ground radar echoes also vary in doppler with your airspeed.

More modern radars can compensate for the doppler shift as your own airspeed is known. The AWG-9 afaik can't and this is clearly described in our source material. Also, newer radars likely have better antennas as well, reducing the sidebands.

This is a deep rabbit hole for sure! I'm just glad that I actually have some education in basic radar technology, helping me make sense of it all! :-)

You guys have it down pretty much.

<snip>

Yeah, and it's MPRF in the more modern radars that makes all the difference. To quote from one of my own technical sources (APG-73):

"MPRF detection is not as good as HPRF, but clutter problems are reduced. Doppler filters are still used to determine target velocity but filers are range gated into bins. Targets are only compared to the clutter that is detected in its range bin".

I'd still like to hear more from Victory on the subject, though. After all, he is the only one who has first-hand experience of it...

The MLC filter on the other hand will move with own aircraft speed as your own airspeed varies making the returned ground radar echoes also vary in doppler with your airspeed.

 

More modern radars can compensate for the doppler shift as your own airspeed is known. The AWG-9 afaik can't and this is clearly described in our source material. Also, newer radars likely have better antennas as well, reducing the sidebands.

 

This is a deep rabbit hole for sure! I'm just glad that I actually have some education in basic radar technology, helping me make sense of it all! :-)

Thanks for the explanation. Yeah, for example, I've read that its replacement, the AN/APG-71, introduced a low sidelobe antenna and a sidelobe blanking guard channel (among some other improvements).

AWG-9 is often mentioned as having been susceptible to ground clutter over land, but I presume it faired much better over the sea as that was its primary mission. Do you perhaps know if this altitude clutter was less significant over the sea compared to over the land?

Also, did you get any information or hints related to performance issues stemming from the fact it only had a high-PRF mode?

Also, did you get any information or hints related to performance issues stemming from the fact it only had a high-PRF mode?

The drawback of High PRF in all doppler systems is that it is more effective for determining relative velocity, but not good for determining exact range at long distance. This is probably why the radar display in PD mode on the AWG-9 only shows closure rate rather than ranging information.

Is that the performance issue you're talking about? Also: where did you read that it only has a high PRF mode? It's true that if the PRF is higher than the rate at which the returns are detected then the range info will be unintelligible which is bad for missile tracking, but since the radar was designed to guide missiles, it would make sense that is has a low PRF mode for target tracking.

Edit: This is from the EA manual: The six round buttons, which are labelled 5, 10, 20, 50, 100 and 200, are used to set desired radar range in pulse modes and IFF range, they also set the scale on the pilot target range displays. The buttons are mutually exclusive as only one range can be selected at a time. In pulse search this setting affects the PRF of the radar and the scale on the DDD and if set to 20nm or greater range it also enables pulse compression. (http://www.heatblur.se/F-14Manual/general.html#an-awg-9-weapon-control-system-wcs)

I assume HB wouldn't have modeled this if their source material disagreed, so yeah it's totally capable of changing its pulse frequency.

Is that the performance issue you're talking about? Also: where did you read that it only has a high PRF mode? It's true that if the PRF is higher than the rate at which the returns are detected then the range info will be unintelligible which is bad for missile tracking, but since the radar was designed to guide missiles, it would make sense that is has a low PRF mode for target tracking.

 

Edit: This is from the EA manual: The six round buttons, which are labelled 5, 10, 20, 50, 100 and 200, are used to set desired radar range in pulse modes and IFF range, they also set the scale on the pilot target range displays. The buttons are mutually exclusive as only one range can be selected at a time. In pulse search this setting affects the PRF of the radar and the scale on the DDD and if set to 20nm or greater range it also enables pulse compression. (http://www.heatblur.se/F-14Manual/general.html#an-awg-9-weapon-control-system-wcs)

 

I assume HB wouldn't have modeled this if their source material disagreed, so yeah it's totally capable of changing its pulse frequency.

Currently in DCS, there is a standard radar model in which the high-PRF is optimally used for the approaching targets, while it has problems detecting receding ones, so medium PRF is used for those (e.g. on MiG-29, F-15C, etc.). Realistically, IIRC, medium-PRF is also a better choice up-close, but it has a shorter detection range. I know this model is rather simplified, but still, it has to be based on some facts. E.g. the MiG-29 manual calls these different modes "Encounter" and "Pursuit".

Since I don't recall seeing the cockpit controls for the PRF mode setting in Pulse-Doppler mode, I searched on the net about the AWG-9 and high-PRF and found mentions supporting only high-PRF PD mode, while AN/APG-71, being a more modern radar, also introduced a medium-PRF mode.

Of course, since -1A NATOPS manuals are restricted, what I'd expect is one of the few places this kind of information on it is described in more detail, I can't find any official confirmation, otherwise I would have posted something more than just 'I've seen mentions of it'.

E.g. http://what-when-how.com/military-weapons/sensors-and-electronic-warfare-military-weapons/

The AN/APG-71 fire control radar is an upgrade of the AWG-9 weapons control system used in the US Navy F-14 Tomcat. It also shares 86% of the Shop-Replaceable Assemblies (SRA) with the

APG-70 flown in the F-15C/E. The APG-71 is basically a digital version ofthe AWG-9 but represents a reworking of virtually every part of the system; only the transmitter, power supply, and aft cockpit tactical information display are retained from the AWG-9. Detection and tracking ranges increase by 40%, while reliability is expected to double in hours between failures.

A new broadband radar master oscillator contributes to improved Electronic Counter-Countermeasures (ECCM) capabilities. The analog-to-digital converter is claimed by Hughes to be state-of-the-art. The antenna control allows for more flexible search patterns than those of the AWG-9.

The fully programmable, four-unit signal processor and improved radar data processor permit greater simultaneous coverage of opening (target moving away) and closing (target heading toward aircraft) speeds. Additional modes permit Beyond Visual Range (BVR) target identification, raid assessment with high-resolution Doppler techniques to distinguish among closely spaced targets, monopulse angle tracking to predict the future position of a single target during high-speed maneuvers, and distortionless sector ground mapping of both ocean and land areas.

The APG-71 can also be linked to Infrared Search and Tracking (IRST) for passive, long-range search making little

use of the active radar. Digital scan control and improved frequency agility are also part of the upgrade.

The advanced low-sidelobe antenna is more difficult to jam. Its mount is different, but the antenna retains the gimbal system used in the AWG-9.

Further improvements planned or proposed for the APG-71 cover virtually every operational facet. Budget stringencies battle with the newly enhanced air-to-ground role envisioned for the F-14 to determine which shall be funded. They include:

• adding a medium Pulse Repetition Frequency (PRF) capability for air combat maneuvering

• interleaving high- and low-PRF waveforms for improved detection at greater range

• modifying the frequency modulation of the ranging Doppler to operate over a greater range

• improving ground clutter definition and ground moving-target indication and tracking

• manual terrain avoidance and clearance

• improved look-down, shoot-down capability over land

• adding high-resolution synthetic aperture and inverse synthetic aperture modes

Okay, fair enough. The AWG-9 is pretty old, after all. So what’s the specific question you want answered? Not that i’ll definitely know the answer, but just ask it plainly so more people can see. Someone will know.

I'd still like to hear more from Victory on the subject, though. After all, he is the only one who has first-hand experience of it...

We already heard from him. He said the AWG9 worked fine in a tail chase, co-speed scenario. I think we would need to ask a Tomcat RIO for actual first-hand experience (after all Victory just drove the thing ;)), but my guess is that a good RIO could work past the limitations in that case, either by changing geometries or switching to another mode of the radar.

Okay, fair enough. The AWG-9 is pretty old, after all. So what’s the specific question you want answered? Not that i’ll definitely know the answer, but just ask it plainly so more people can see. Someone will know.

I don't have time right now to acquaint myself with the radar physics and stuff to be able to post well informed questions nor do I know how the HB radar model is designed, but all these documents about the AN/APG-71 upgrade that can be found on the net, mention how it fixes deficiencies of the AWG-9, namely:

- being high-PRF only (so, in simplified radar modeling, some issues regarding detection of receding targets should be present, I guess)

- having poor look-down performance over land (distinguishing targets from the ground clutter)

- being more susceptible to ECM due to its non-low sidelobe antenna design

My question would be if the HB SME's they worked with provided any hints regarding AWG-9 weak spots or especially these points in particular. If so, is something implemented in the radar model regarding this, if not, perhaps they check with them about these officially known deficiencies?

Of course, perhaps the AWG-9 is still classified related to Iran owning them, but the points I mentioned are openly available on the net so implementing some of these issues in the sim if indeed present and possible to implement would not provide any new information I guess.

Regarding the AWG-9 Pulse modes and PRF, apparently low-PRF is used for those, not high which was required for PD modes. It's mentioned that it was kept for ACM and all-aspect performance, so I presume that means to offset the limitations of high-PRF in some scenarios (e.g. receding or close targets).

Hi all, some wonderfully technical information here in this post although, practically all of it is over my head, however it is clearly obvious that you fine people are just the radar boffins to ask my simple newbie question too...!

Ok, so hear is my simple question, I’ve been trying to get an aircraft blip on my RIO radar for the last 5 days with not a single occurrence of anything at all... Nothing, nil, zero...

I’ve been through the manual, watched some wonderful videos (obviously including this one), tried different aircraft from different speeds, heights, angles and distances. Different multiplayer servers... Absolutely everything I can think of but still no blips... (the kind gentleman who pilots for me is very patient thankfully).

I’ve been through the training missions where everything works perfectly and have no issues finding the blips in all the different modes, hooking them, IFF, all no problems... Get into the back of a hot start Multiplayer F-14 and Nothing...!

There must be a button, switch, setting or something I’m missing that’s not shown in the training missions or videos that everyone knows about besides me...

I would really appreciate if someone could give me a leg up on this as I’m absolutely stumped. I’m sure I’ll be away and running if I could get it to work just once...

Thank you all in advance and have a wonderful day.

Really hard to judge Space Cadet. Have you tried it from a cold dark start? It's quite possibly a simple switch that just hasn't been set in a hot start plane.

Here is another great Jabbers video on the start-up from the back seat:

Hi all, some wonderfully technical information here in this post although, practically all of it is over my head, however it is clearly obvious that you fine people are just the radar boffins to ask my simple newbie question too...!

 

Ok, so hear is my simple question, I’ve been trying to get an aircraft blip on my RIO radar for the last 5 days with not a single occurrence of anything at all... Nothing, nil, zero...

 

I’ve been through the manual, watched some wonderful videos (obviously including this one), tried different aircraft from different speeds, heights, angles and distances. Different multiplayer servers... Absolutely everything I can think of but still no blips... (the kind gentleman who pilots for me is very patient thankfully).

 

I’ve been through the training missions where everything works perfectly and have no issues finding the blips in all the different modes, hooking them, IFF, all no problems... Get into the back of a hot start Multiplayer F-14 and Nothing...!

 

There must be a button, switch, setting or something I’m missing that’s not shown in the training missions or videos that everyone knows about besides me...

 

I would really appreciate if someone could give me a leg up on this as I’m absolutely stumped. I’m sure I’ll be away and running if I could get it to work just once...

 

Thank you all in advance and have a wonderful day.

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Stupid question, but are you sure you out the WCS in 'on' and not 'standby' ? (Switch on the right of the hcu)

 

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Most likely this