Newbie radar question

[tagge]

Hello all! My first post on this forum.

 

Been flying Lock On since january 2010, mostly SU-27, SU-33 and MIG-29.

 

A few questions, gentlemen, if i may;

 

A) What does the three modes mean in "Change radar modes" (RWin +I), Interleaved PRF (AUT), HI PRF (PPS) and MED PRF (ZPS)?

 

B) The keycard mentiones "autopilot mode - radio altitude hold" (Alt +5). Shouldn't that be "radar altitude hold"?

[zakobi]

Hello all! My first post on this forum.

 

Been flying Lock On since january 2010, mostly SU-27, SU-33 and MIG-29.

 

A few questions, gentlemen, if i may;

 

A) What does the three modes mean in "Change radar modes" (RWin +I), Interleaved PRF (AUT), HI PRF (PPS) and MED PRF (ZPS)?

 

B) The keycard mentiones "autopilot mode - radio altitude hold" (Alt +5). Shouldn't that be "radar altitude hold"?

 

At b both are technically correct. Radar (originally RADAR) is an abbreviation of RAdio Detection And Ranging

 

For a i can't help that much, but try see if there's anything useful and helpful at this site: http://flankertraining.com/ironhand/index.html

[Frostie]

A) What does the three modes mean in "Change radar modes" (RWin +I), Interleaved PRF (AUT), HI PRF (PPS) and MED PRF (ZPS)?

 

HI PRF, HI (ППС, in Russian HUD) for approaching targets, has the longest range

 

MED PRF, MED (ЗПС ) for running targets, has the shortest range

 

Interleaved PRF, ILV (АВТ) default uses both HI and MED with a slight reduction in range than HI.

[GGTharos]

It also suffers a reduction in detection and lock on range of receding targets. MPRF gives you the best performance against receding targets.

[tagge]

Thanks guys, very helpfull information.

 

One more question:

 

What's the difference between "H" - toggle altitude stabilization and "Alt + 4" autopilot -barometric altitude hold?

 

Aren't they both barometric?

[mig29]

Interleaved PRF has a range penalty of 25%.

[zakobi]

Thanks guys, very helpfull information.

 

One more question:

 

What's the difference between "H" - toggle altitude stabilization and "Alt + 4" autopilot -barometric altitude hold?

 

Aren't they both barometric?

 

Afaik the Alt+# AP's was introduced because of the Su-25T

[Scabbers]

PRF=Pulse Repitition Frequency The higher the frequency the greater the resolution of the scan. Also requires more power and creates more demand on the kylstron.

 

This being said with high PRF you get a better track on an approaching target because you have more scanns on the track to show changes in didstance. For a track extending from you a lower PRF will do the same job.

[GGTharos]

PRF=Pulse Repitition Frequency The higher the frequency the greater the resolution of the scan. Also requires more power and creates more demand on the kylstron.

 

... which fighters don't use today AFAIK, they tend to use TWTs or better.

 

This being said with high PRF you get a better track on an approaching target because you have more scanns on the track to show changes in didstance. For a track extending from you a lower PRF will do the same job.

 

Actually a lower PRF will perform better in the receding target situation. Why are you giving people wrong information?

[Scabbers]

GG i am not sure that you understood what I posted.

[Scabbers]

At long wavelengths (eg. 50 metres) only large objects will reflect back a complete radiation pattern for collection. Therefore, if small objects (such as a fighter plane) need to be accurately recorded, much shorter wavelengths must be employed. Atmospheric interference is also less pronounced at shorter wavelengths.

 

This is really basic theory and maybe states what i said with a little more accuarcy.

[GGTharos]

What does that have to do with PRF? Fighter radars operate in the X-Band which is betweet about 2.5cm and 4cm. PRF is how often you repeat the radar pulses, not what their wavelength/frequency is.

[Sticky]

GG i am not sure that you understood what I posted.

 

Perhaps you misunderstood the thread title :music_whistling: It wasnt supposed to say Newbies answer radar questions ;)

 

JK!!:cheer3nc:

[mig29]

The exact text from the manual...

 

The expected target aspect hemisphere is controlled with the [RShift-I] key. АВТ (ILV) mode can be used if the target aspect is unknown. The expected target aspect determines the pulse repetition frequency (PRF) to be used by the fighter radar in search mode. High PRF (HPRF), which provides the longest detection range against approaching forward-hemisphere targets, is indicated by ППС (HI), whereas medium PRF (MPRF) for receding rear-hemisphere targets is indicated by ЗПС (MED). In АВТ (ILV) mode, high and medium PRFs are interleaved on alternate bars of the radar scan pattern. This provides all-aspect target detection at the expense of a 25% reduction in maximum range.

 

:pilotfly:

[vanir]

Actually this tech talk brings up an interesting point, looking at it with very little hands on physics experience but just as a pragmatist.

 

I've occasionally wondered at russian-english translation with lock on. Is it possible PRF describes signal wavelength with poor transliteration?

 

Just thinking logically, and obviously I could be way off, first time I've thought of it and I just woke up.

But if you had an approaching target you could afford to pulse less frequently to paint it. If it was receding you would have to pulse more frequently to paint it.

 

On the other hand with the signal itself, irrespective of approaching/receding targets over a shorter distance you'll get away with slower frequencies with beam coherence and over longer ones you'll want faster frequencies so there's still a beam reflection to pick up.

 

So high PRF as described seems counter-intuitive, unless it was a poor transliteration for signal frequency and not pulse frequency.

 

It's just that the ability of Russian radars to piggy back multiple signal frequencies is published (listed as for the purposes of increasing ECCM).

 

Anything to it or am I confused?

[GGTharos]

I've occasionally wondered at russian-english translation with lock on. Is it possible PRF describes signal wavelength with poor transliteration?

 

No, it does not. It describes the pulse repetition frequency.

 

Just thinking logically, and obviously I could be way off, first time I've thought of it and I just woke up.

But if you had an approaching target you could afford to pulse less frequently to paint it. If it was receding you would have to pulse more frequently to paint it.

Actually high PRF = higher energy = longer range detection, but it has range ambiguity. High PRF gives a high probability of detection against high doppler-shifted targets (ie. high closure targets). MPRF gives better detection against low closure targets because doppler shift resolution and ambiguity is better than HPRF, IIRC.

 

On the other hand with the signal itself, irrespective of approaching/receding targets over a shorter distance you'll get away with slower frequencies with beam coherence and over longer ones you'll want faster frequencies so there's still a beam reflection to pick up.

 

So high PRF as described seems counter-intuitive, unless it was a poor transliteration for signal frequency and not pulse frequency.

No it is the correct translation.

 

It's just that the ability of Russian radars to piggy back multiple signal frequencies is published (listed as for the purposes of increasing ECCM).

 

Anything to it or am I confused?

Yeah, you're confused. Piggy back multiple signal frequencies? I think not; their ECCM capability (of the original flanker and mig radar) is inferior to the western MSA's due to weaker processors and the physical design of the antenna. Edited October 1, 2010 by GGTharos

[tagge]

Perhaps you misunderstood the thread title :music_whistling: It wasnt supposed to say Newbies answer radar questions ;)

 

 

Heheheheheh... right. Just some simple questions from a newbie. Intersting disscussion, though.

 

Any comments on the barometric altitude question?

[GGTharos]

H is the old autopilot logic, and yes, it should be baro, and alt-4 is the new (Su-25) autopilot logic.

[tagge]

H is the old autopilot logic, and yes, it should be baro, and alt-4 is the new (Su-25) autopilot logic.

 

Yeah, but how do they differ from each other? Isn't barometric altitude = barmometric altitude?

[GGTharos]

I don't know. There might be differences in the autopilot logic, and it might be more of an issue with AFM rather than SFM aircraft.

[vanir]

I don't know, I was simply reading an engineer's report on the old smerch on the web describing it's jam proof capabilities being provided by its signal being a powerful emission of multiple frequencies. Piggy back was the term he used.

 

Naturally I figured a linear progression with Russian radar development. You can trace the Fulcrum radar right back to the Flogger for example.

[mig29]

The following two links might throw some light ...

 

http://en.wikipedia.org/wiki/Radar_Signal_Characteristics#Unambiguous_range

 

http://en.wikipedia.org/wiki/Pulse_repetition_frequency

[vanir]

what amazes me is that early radar operators simply looked at a wavelength signal on a small screen and told you what you were looking at, how far away it was, etc.

For example air intercept radar operators on British WW2 bombers. They have been described as "extremely talented individuals, chosen for instinctive ability to read signals and make any sense of them"

[GGTharos]

Wavelength isn't exactly what they were looking at. They were looking at what you might think of as 'raw' data, but even that was actually somewhat processes. But, that is picking nits. :D