HPRF in TWS / RWS question

[twistking]

Quick question about pulse repetition frequencies.

Wag's new video makes it seem as if interleaving MPRF and HPRF was the "secret sauce" of the upcoming Velocity Search mode. He does not mention any other technicalities that distinguish it from RWS. Does that mean, that RWS and TWS both use MPRF exclusively? I somehow assumed that RWS and TWS would also use interleaved HPRF/MPRF. Can someone clarify? Is Velocity Search basically the Viper's way of doing HPRF?

Bonus question: Is Velocity Search constantly interleaving, or does it only ping MPRF once a target is detected in the HPRF bit? If it constantly interleaves, it should be able to also detect cold targets, no?

Edited June 5, 2023 by twistking

[alexscott292]

I think that someone who can give you a detailed answer probably won't lest they go to prison.

In general, in a pulse doppler system analysing any individual returned pulse can give you a velocity, but if you want to look at range and velocity together high pulse repetition frequencies drastically limit the range - there is the phenomenon of aliaising, in lay terms the radar can't tell whether the return it's looking at is from one pulse retunred from far away or the next pulse much closer.  The pulse has to be transmitted, reflected and received before the next pulse is sent.

The problem with cold targets is that doppler relies on velocity difference between the transmitter and the target - the transmitter is moving.  So if you have two jets moving at very similar velocities and the target is nose cold/low aspect, the velocity difference is close to zero.

These are problems that also affect medical ultrasound.  When you want to look at blood flow, Murphy dictates the only view you get will have blood flow at 90 degrees to the probe.  Effectively the blood flow notches itself because Murphy.

[Aquorys]

On 6/6/2023 at 12:43 AM, twistking said:

Wag's new video makes it seem as if interleaving MPRF and HPRF was the "secret sauce" of the upcoming Velocity Search mode. He does not mention any other technicalities that distinguish it from RWS.

SAM is only available from RWS, VSR is more accurate with regards to range and avoids incorrect range readings

On 6/6/2023 at 12:43 AM, twistking said:

If it constantly interleaves, it should be able to also detect cold targets, no?

VSR is programmed to detect and range hot targets only

The exact details of what mode uses what PRFs and when and how it does so are classified. Furthermore, the radar is generally software-controlled, and there can be differences, roughly speaking, depending on whose aircraft it is (e.g., US vs. export) and whether some advanced features have been activated or not.

[twistking]

Thanks for the answers. So to sumamrize, one can say that VSR is a bit more more complex than just doing interleaved Hi/Med PRF and RWS is more a bit more complex than doing just Med PRF.

[itn]

For Viper VSR it's sort of "search + confirm". So basically it should do normal Velocity Search using HPRF, and when it gets hits, it "verifies" them with some sort of MPRF scan. My understanding is that unless you get hits, it just keeps scanning in HPRF, unlike the interleaved mode(s) in Hornet.

See for example Introduction to Airborne Radar and Principles of Modern Radar Vol. III: Radar Applications. Nothing classified about the overall strengths, weaknesses and features of L/M/H PRF, even if details and actual frequencies and patterns are classified. I don't know much about radars or radar theory, and am not trying to portray an expert here, but it's laid out pretty clearly.