F-15C radar questions

[SDsc0rch]

RWS and TWS - yes, the scan pattern is pitch/roll-stabilized

 

auto-ACQ modes - no, the scan pattern remains fixed relative to the airframe

[TAW_Blaze]

RWS and TWS - yes, the scan pattern is pitch/roll-stabilized

 

auto-ACQ modes - no, the scan pattern remains fixed relative to the airframe

 

Edit: after reading your PM ( your inbox is full, can't reply, but I want it in the post anyway)

 

There's a bit of missunderstanding here. We are trying to find out if the F-15C's radar is stabilized in game, not in real life. AAQ modes are most likely not stabilized, the opposite would be quite counterproductive. However RWS/TWS stabilization is not quite obvious (in DCS, anyway).

Edited September 9, 2014 by <Blaze>

[GGTharos]

I don't understand the question. The flood horn is a separate flood horn, it doesn't use the dish.

 

The one burning question I have, is the transmitter on the radar is it always in flood of the full 60* or is it only transmitting in the same direction as the receiver? Curious on this as I'd think that if it was transmitting just on the same azimuth there would be a delay.

[TAW_Blaze]

I'm really not sure what he means either but this is my guess:

 

I think what he's trying to say is that if you transmit do you wait before moving the antenna to receieve the echo from X reasonable max range or you move it without waiting. I have no idea how that works.

[GGTharos]

The antenna moves quite slowly compared to the send and listen time for the train.

 

In other words, the radar sends and listens while looking in a specific direction. It does not flood - flood transmits continuously, normal radar operation has a transmit-receive cycle.

[TAW_Blaze]

In case of a planar array antenna they are slightly behind it IIRC. There are some holes on the dish and the radio waves are transmitted through them. I'm reading Stimson's book atm but I've only started it a few weeks ago and I have a hard time understanding a lot of stuff - english is not my mother tongue after all.

 

As for constant flood there is no such thing really, as GG said, pulse doppler radars have a duty cycle and very little part of that is spent actually radiating.

 

or just constantly flooding in all direction on both vert and horizontal axis.

 

That wouldn't make a hell of a lot of sense though. :D

[GGTharos]

This would be close to what I mean.. I guess my question would be is the transmitter on the dish it self or is it off the dish and in a fix constant flood or pulse transmit and the dish moves picking up echo's from the constant flood or flood?

 

The transmitter is actually a box inside the nose, which sends the signal to either the dish or flood horn to transmit. So, the signal is generated back there, and transmitted through the dish or horn.

 

I understand that when the radar is in flood or vert scan the dish would be straight or tilted up in respects to those modes. I'm just curios if the transmitter is paired to the dish or just constantly flooding in all direction on both vert and horizontal axis when it transmits.

 

The FLOOD horn is a SEPARATE piece of equipment from the radar dish. They don't work together. You don't flood with the dish, and you don't detect with the horn.

 

You don't flood with the horn and listen with the dish, either. The FLOOD horn is used in very specific situations, namely if SARH guidance is dropped within a certain range or if a sparrow is launched without STT, or if selected by the pilot. It is used to guide an AIM-7 at relatively close range and nothing else.

 

Don't confuse AACQ modes with FLOOD. They are NOT the same.

[TAW_Blaze]

 

They scan in a specific pattern generally defined as X-bar scan. One bar is usually as much as the radar can scan without moving the dish (in the vertical). I think this pretty much answers your question.

[TAW_Blaze]

The thing is, it can't. Even for a 1-bar scan you have to rotate the antenna in the horizontal. There is a specific cone that you can scan without rotating at all and it's not very large. Mechanical antenna rotation takes a lot more time than transmitting. This is the exact reason why AESA is so powerful, because there's no need for mechanical steering.

[GGTharos]

Ok so I'm confusing you.. Yes I understand the signal is generated back there.. So the dish actual has a transmitter on it along with antennas to pick up echo returns. therefor the standard functions of the radar are paired to the dish. I.e where the dish it pointing is where the transmitter is directing radio energy.

 

No, the dish has no transmitter on it. It is the antenna, so the signal is transmitted and received through it.

 

The transmitter is a box that sits inside the avionics bay in the nose, and is somewhere behind the dish. It can send its signal through the dish or the flood horn.

[GGTharos]

Flooding = constantly transmitting, especially when used in the context of the F-15. If you want to say something else, use another word.

 

Radar antennas are highly directional - the mechanicals by being scanned, the electronic ones by pointing the mainlobe. If you do what you're suggesting, you will get much less range for the same power, assuming I understood what you're saying.

 

THis still wouldn't answer my question truly. that could also just be looked at that is all the dish could see at any give point of time. To me, I would say that if a radar system was constantly flooding [not constantly transmitting] all areas that the dish could pick up more echo returns further out, it would be better at seaching.. But I just answered me question thinking about STT. when all radar engergy is pointed directly as a target would deduce that the transmitter is paired to the dish.

[TAW_Blaze]

What im saying is if the trans mitter is transmitting in all directions apart from the dish.

 

I think that's not possible in case of a planar array. It'll only scan in the direction the dish is pointed. It's not by coincidence you have to rotate around the dish to complete a multiple bar scan. An AESA can do it though. But an AESA doesn't even have a rotating dish. :)

 

That when the dish is a x azmith it does not have stay there to transmit then wait for echo return before tilting to look at another area.

 

I don't understand how this relates to the sentence before. But we answered this, the echoes are received faster than the mechanical movement of the antenna. So it basically doesn't matter.

[VTJS17_Fire]

To amplify what Exorcet is saying, when you bump the TDC up against the top of the VSD and the range changes from, say 20nm to 40 nm, you are simply asking the VSD what the radar is picking up out to that higher distance. When you bump down from 40nm to 20nm, you are simply asking the VSD only to display what the radar is picking up out to 20nm. In both cases the radar's range hasn't changed, only what you are asking the VSD to display.

 

EDIT: I created some instructional videos some time ago on my website that you might find helpful. Just click my signature and it'll take to to the site. They're also kicking around on YouTube uploaded by other folks.

 

 

Rich

I know your vids, watched it a few years ago.

 

I knew, that I understand the Radar and VSD. Only this comment on YT confused me, due to my knowledge .. :doh:

 

Thanks for confirm, what I knew. :thumbup:

[Ironhand]

Youre thinking that i dont understand the dish cannot see all coverage at once. I understand that it has to tilt both left and right along with up and down.

What im saying is if the trans mitter is transmitting in all directions apart from the dish. That when the dish is a x azmith it does not have stay there to transmit then wait for echo return before tilting to look at another area.

I think the part you're missing is that the transmitter simply generates, in pulse Doppler mode, the signal pulse at a certain strength and frequency. That's all it does "part from the dish". The pulse is sent out through the dish. The single pulse goes where the dish is pointing. If it hits anything, some of it is reflected back while the antenna is still pointing in that direction and the antenna receives it. After a specific wait time, the next pulse is sent out. Again where the dish is pointing. Granted the wait time is very short since the pulse is traveling at the speed of light (or so I recall). So everything is happening very quickly. But the transmitter is not "flooding" (to use your term) the entire 60* cone with energy. Just the discreet piece of sky the cone is pointing at. At least that's been my understanding of how it all works in layman's terms.

 

 

...Only this comment on YT confused me, due to my knowledge .. :doh:

 

Thanks for confirm, what I knew. :thumbup:

You're welcome. You gave me a scare. For a minute you had me thinking that I had made that statement in the tutorial. It wasn't until I went to YouTube and started scanning the comments section that I saw what you were referring to. :)

 

Rich

Edited September 10, 2014 by Ironhand

[85th_Maverick]

Thanks for the help everyone - now I understand where I was thinking wrong. I still don't get it what happens when the radar is pointed upwards, but that is not important, probably.

 

Another question - when the plane rolls - does the radar compensate or it rolls with the aircraft?

 

 

This might be a way it stabilizes it's orientation and/or remains on a locked signal, not just for russian fighters, but also for others:

 

(at 0:21 second you can see it rolling)

[GGTharos]

The dish is the antenna. Not on, not behind or in front, the dish is it :)

 

It also has the IFF TX mounted on it, but those are separate antennae, they're just mounted on the dish.

 

As for doing what you suggest with the transmitter, I'll try to guide you in the right direction regarding the 'why not'.

 

The radio signal loses power proportional to r^2 (r being distance from transmitter), and if you want to detect the reflection from the target, it's r^4.

 

Now, you have guessed that realistically, the radar energy is spread out over the area of the beam width - usually we talk about bea-width in degrees, and IIRC for the F-15 it is 1.5 degrees. To add to that, 1.5 degrees is a different area based on distance, since an object that is further away need to be larger to appear to have the same angular size to a closer object.

 

Now imagine if you tried to take that 1.5deg and try to belt out the same power in a 60 deg cone. You'd basically spread out the radio energy so thin that you would cut your radar detection range to nothing.

[Altimaden]

after reading the thread, i think most of the ambiguity comes from the geometric concept of a radar cone.

when an angle is referred to, it is a 2 dimensional figure, but when it comes to a 3 dimensional radar search cone, an 'angle' actually means a 'solid angle'

 

from what i gather, a radar is like a cathode ray tube monitor - in that a small beam (the arrow in the figure) is pulsed over the search area (area A) in a however many bar zig-zag, and the difference in the reflected image over time builds up a scan picture - so for the F-15C in game IIRC takes 2 and a half seconds to build a complete image...am i close?

[Ironhand]

...

 

from what i gather, a radar is like a cathode ray tube monitor - in that a small beam (the arrow in the figure) is pulsed over the search area (area A) in a however many bar zig-zag, and the difference in the reflected image over time builds up a scan picture - so for the F-15C in game IIRC takes 2 and a half seconds to build a complete image...am i close?

That is my understanding as well. Don't know about the exact time span involved but, for a 60* scan, I'd say it was probably close.

 

Rich

[GGTharos]

Not even close. It's 70 deg/s and it can be faster or slower depending on radar mode or settings. So generally 1 bar will be scanned in a little under 2sec.

[Oberst Zeisig]

One thing that interest me in that context:

 

The 1 bar scan has a vertical width of about 10deg. So I suppose the antenna (moving from left to right and back) has a streaming zone of 10deg.

 

So why is it in bore mode where the radar antenna look straight forward You have only that small zone of about 1.5 deg. in the inner circle on the HUD where You can autolock targets. Why ins't that zone not also 10deg? (maybe pictured by the outer circle on the HUD in bore mode)

[Bushmanni]

Four bars is 10 degrees, so one bar would be 2.5 degrees.

[Svend_Dellepude]

One thing that interest me in that context:

 

The 1 bar scan has a vertical width of about 10deg. So I suppose the antenna (moving from left to right and back) has a streaming zone of 10deg.

 

So why is it in bore mode where the radar antenna look straight forward You have only that small zone of about 1.5 deg. in the inner circle on the HUD where You can autolock targets. Why ins't that zone not also 10deg? (maybe pictured by the outer circle on the HUD in bore mode)

 

The F-15 should also have a mode called supersearch, which works in a similar fashion as the BORE mode but covers a larger area. Not modeled though.

[Oberst Zeisig]

Four bars is 10 degrees, so one bar would be 2.5 degrees.

 

Sure about that? 4 bar scan isn't modelled in the game only one bar scan. And this covers, if You calculate it according distance and vertical coverage (so simple geometry), round about 10 degrees. That's also a number I read in the forum before.

[Oberst Zeisig]

The F-15 should also have a mode called supersearch, which works in a similar fashion as the BORE mode but covers a larger area. Not modeled though.

 

That would be so cool. The perfect mode to reacquire targets that You know are somewhere nearby.

There are so many features and modes and functions for that radar that aren't modelled and bring You deceicive advantages. It really is time for a DCS:F-15C.

[Bushmanni]

Real 4 bar scan is 10 degrees and that's what DCS manual also says about LRS scan pattern height. Also contacts on radar scope are updated in four distinct bars. It's hard to notice unless you create a scenario that shows it in a clear fashion.