prf radar modes

[Azrayen]

So, Am I correct, assuming that for removing the problem of detecting a nearly 0 relative velocity target against the sky you simply switch the doppler filter off, as soon as that is implemented, and you only switch to low prf if its below the horizon and hope the target reflection is stronger then the ground returns you are getting ?

That would actually make sense to me :D

That's how FC radar are modelized.

Makes sense indeed.

I'm advocating for this to be implemented here too. Would limit the lock losses when target is at/above own altitude. And seems realistic.

FC uses a kind of radar horizon, i.e. not sure it takes moutains into account. Would be nicer if they would be taken into account.

[sedenion]

FC uses a kind of radar horizon, i.e. not sure it takes moutains into account. Would be nicer if they would be taken into account.

 

That would be very odd ED don't implemented a ray casting for ground vs target z-sorting, it's some elementary process. As far as i know, a target behind a mountain cannot be detected, so the z-sorting data exists... behind or front of, you choose what to do with that data, occlusion or ground clutter.

[Azrayen]

No no that's not what I'm saying.

 

Of course ground masks are implemented.

 

I was only talking about determining if the target is in look-up or in look-down (= is my radar using doppler filter i.e. is it prone to be blinded by a notch/beam?).

For this (and this only) I think ED uses a "radar horizon" and I don't think (I can be mistaken) that this radar horizon takes relief into account.

 

This is old memory from FC or FC2.

 

++

Az'

[sedenion]

No no that's not what I'm saying.

 

Of course ground masks are implemented.

 

I was only talking about determining if the target is in look-up or in look-down (= is my radar using doppler filter i.e. is it prone to be blinded by a notch/beam?).

For this (and this only) I think ED uses a "radar horizon" and I don't think (I can be mistaken) that this radar horizon takes relief into account.

 

Ok, i don't know how real radars work and how that should work... i can only tell that it appear simpler to use the "ground occlusion" algorithm to do this (so it should take mountains into account de facto) ... But, real radars actually take reliefs into account in this kind of situation ? Don't they simply use some average "horizon" level to "split" the dectection area (wich should obviously produce some problems near horizon if there is mountains) ?

[jojo]

A good summary, better than what I can explain :D

Note, you can't select MPRF in M-2000C...

[Dave317]

Help me out here, I'm still confused. I'm having a hard time finding targets sometimes even when there are within 10 miles.

If I'm flying towards the battle and looking for targets. Which mode is best? Once I'm in a close fight what mode should I use then?

[ZHeN]

yesterday I couldn't find target on my radar, which was moving away from me, and I saw it with my eyeball mk. 1, I guess range was <10NM ... same issue, Dave

I tried switching between PRF's, but it didn't help. Same for CCM. Even Magic II had it's lock on the target, but radar couldn't find it :doh:

[mia389]

yesterday I couldn't find target on my radar, which was moving away from me, and I saw it with my eyeball mk. 1, I guess range was <10NM ... same issue, Dave

I tried switching between PRF's, but it didn't help. Same for CCM. Even Magic II had it's lock on the target, but radar couldn't find it :doh:

 

In this case I would of went to bore sight. This happens to me in the F15 as well. Instead of changing radar prfs, moving cursor and tilting radar, its just easier to switch to boresight and lock aircraft.

[ZHeN]

In this case I would of went to bore sight. This happens to me in the F15 as well. Instead of changing radar prfs, moving cursor and tilting radar, its just easier to switch to boresight and lock aircraft.

 

tried that too

didn't work

[Joni]

Wikipedia article on PRF is just confusing. First of all you need to know that high PRF mode is different from low PRF (and med PRF) in many other ways than just the PRF. Most important secondary difference is pulse width and duty cycle which is the ratio of pulse width to pulse repetition interval.

 

Since high PRF has small unambiguous range detection capability it has to use different method for ranging than direct pulse flight time measurement. Essentially high PRF mode encodes each pulse so you can later identify the original pulse from the reflection and then calculate the pulse flight time. This method reduces range resolution. As you now use a different method for ranging echoes, you can ramp up duty cycle as much as you want (all the way to 50%, ie. the radar spends equal time sending and listening) to output as much energy as possible. This gives the high PRF the long detection range it's famous for. You also get the best frequency resolution due to high PRF and therefore good clutter rejection.

 

Low PRF has small pulse width and large pulse interval hence low duty cycle. Low duty cycle is essential for large unambiguous range measurement capability. Low PRF mode can't use doppler frequency detection so it's essentially a pulse radar mode (like the radar in MiG-21). Hence it can't filter out ground returns by doppler shift either. You can still detect targets if you set up the geometry so that ground clutter is minimized (target above horizon and radar sufficiently high above ground) or target is so close that the target has stronger echo than the ground. You can also see targets below horizon if the "ground" doesn't produce much echoes like over calm sea. What you see displayed is something like a weather radar or marine radar. Because of small pulse width LPRF has superior range resolution. On the other hand because of small duty cycle it has low average power and hence low detection range.

 

Range resolution plays a role when trying to detect two targets flying close to each other. When you have good range resolution, the targets need to fly much closer to be detected as single target compared to if you had bad range resolution. DCS doesn't model resolution cells so all radars have infinitely small resolution cells and therefore you cant hide your presence by flying close to another plane.

 

 

Pulse width is automatic based on selected radar range. So if you are in high prf the computer automatically calculates how much time the pulse will last (pulse width) to reach selected range based on the amount of pulses per second (prf) that are being thrown into space.

 

Pulse Repetition Time=Pulse Width+Listening Time

 

 

What Im not sure is if there can be more than one pulse in nanoseconds which are considered just "one pulse".

[Joni]

yesterday I couldn't find target on my radar, which was moving away from me, and I saw it with my eyeball mk. 1, I guess range was <10NM ... same issue, Dave

I tried switching between PRF's, but it didn't help. Same for CCM. Even Magic II had it's lock on the target, but radar couldn't find it :doh:

 

Thats called sidelobe clutter since the target was moving away from you and for sure at the same speed.

[Joni]

Also, pulse width is subject to the carrier frequency, is that right?

 

There are still things unclear for me.

[Joni]

 

you can ramp up duty cycle as much as you want (all the way to 50%, ie. the radar spends equal time sending and listening) to output as much energy as possible..

 

Does this mean the carrier frequency can change to have longer pulse width?

[Beamscanner]

Pulse width (also known as pulse duration) has nothing to do with the carrier frequency of a signal.

 

The pulse duration just refers to the duration a radar transmits (the ON time for a single pulse). Usually pulses are between .5 and 100 microseconds long. The longer the pulse, the worse the radars ability to 'break out' closely spaced targets in range (the reflection from two targets may look like one really long return instead of two distinct returns). Thus short pulses have better range resolution (its better at breaking out closely spaced targets on the same bearing). However, shorter pulses means less power on target which equates to less energy reflected. Less energy reflected means shorter detection ranges.

 

Modern radars make use of pulse compression, where a long pulse duration is used to maximize energy on target, but the pulse is modulated with frequency or phase modulation that allows the radar signal processor to section off tiny slices of the pulse to achieve an 'effective' pulse duration much much smaller, giving it excellent range resolution. (best of both worlds)

[Joni]

Modern radars make use of pulse compression, where a long pulse duration is used to maximize energy on target, but the pulse is modulated with frequency or phase modulation that allows the radar signal processor to section off tiny slices of the pulse to achieve an 'effective' pulse duration much much smaller, giving it excellent range resolution. (best of both worlds)

 

Understood everything but the last paragraph.

 

Would you be so kind to tech me more about this? I have been reading a lot of stuff online and Im beginning to understand a lot as well. Just need to polish some things like these.

 

 

Thanks in advance.

[mr_mojo97]

Hi all, not sure if I’ve skipped over this issue as I’m not exactly technically minded but I’ve noticed a fair few times my prf switch automatically switches to brf and squares appear on the radar screen. I have to switch it back to hrf to get my Vs back for a lock on only for them to turn back into squares again and the switch back to brf. Whats happening?

[Joni]

Understood everything but the last paragraph.

 

Would you be so kind to tech me more about this? I have been reading a lot of stuff online and Im beginning to understand a lot as well. Just need to polish some things like these.

 

 

Thanks in advance.

 

Anyone there?

[GGTharos]

Anyone there?

It's a signal processing technique, not relevant to the game.

[Joni]

It's a signal processing technique, not relevant to the game.

 

Im trying to learn here, does not have to be relevant to the game. That's why I was interested in what was mentioned :)

[GGTharos]

Im trying to learn here, does not have to be relevant to the game. That's why I was interested in what was mentioned :)

In that case I suggest investing in the radar Bible or at least look for scholarly articles on the matter. Personally I don't think I can explain it sufficiently:)

[Joni]

Like I said, ive been reading a lot, but still there are things i dont understand :(

[SinusoidDelta]

I don’t wanna be that guy but google something like “Doppler Radar pulse compression”. There are a bunch good documents that can explain the concept.

 

If I explain my understanding I’m only setting myself up to be corrected by beamscanner :smartass:

[vparez]

I'll risk correction, nothing wrong in being corrected you just learn.

 

So, you can modulate the frequency of your pulses, or the duty cycle.

 

The frequency tells you how often a pulse is sent and you can change that continuously so pulses appear gradually more dense, then less dense, and the cycle repeats.

 

If you use PM, then the pulses appear at regular time intervals, but the pulse itself is sometimes shorter and sometimes longer.

 

You can always combine both.

[LowLee]

Pulse modulation and pulse repetition are different things ;)

 

 

 

 

 

 

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inviato con un telefono a gettoni

[Guest]

I'll risk correction, nothing wrong in being corrected you just learn.

 

So, you can modulate the frequency of your pulses, or the duty cycle.

 

The frequency tells you how often a pulse is sent and you can change that continuously so pulses appear gradually more dense, then less dense, and the cycle repeats.

 

If you use PM, then the pulses appear at regular time intervals, but the pulse itself is sometimes shorter and sometimes longer.

 

You can always combine both.

 

 

I dont think thats correct. From what I understood after reading a lot (remember no one wanted to explain and sent me looking for the info myself :D) is that the pulse modulation is modulating the carrier frequency and not the pulse repetition frequency which are two different things.

 

But Im now interested in that PRF modulation. What is it exactly?