The basics of HOJ

[Disso]

It's use has been discussed quite alot lately, however, the basics of HOJ and jamming still need some clarification to me.

 

Am I correct in saying HOJ works like this?:

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The aircraft jams by emitting signals outward in all directions, which gives away the aircraft's general position, yet prevents the enemy from being able to read its direction of flight, distance, altitude, and speed.

 

The Enemy aircraft however can launch a missle which can HOJ, or home on jam. This is done when a missle locks onto the jamming signals instead, and therefore moves in the general direction of the enemy bandit. When the missle gets close enough, and burns through, it then can acquire the bandit on its own, and make the HOJ kill.

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Now was that all Correct?

 

Some questions along side:

 

- Exactly which missles are capable of HOJ?

- Since the missle tracks the jammer and locks onto the aircaft on its own, does that mean, this missle is Fire and forget? Can I unlock the jamming signal?

- Will the enemy get a warning as the missle is fired on the enemies jammer signals instead of on the aircraft itself?

 

Apologies for the barrage of questions, Just needed some clarification.

[Disso]

Bump, Musta' been a bad time to post..

[SwingKid]

There isn't really a "burn-through" in the popular sense (at least, not as represented in Lock On - that model is a simplified compromise between real-world ECM and ECCM tactics that aren't modeled). The HOJ missile generally homes onto the jamming signal all the way to impact, just like a Sidewinder homes onto heat emissions all the way to impact.

 

Generally speaking, any missile with a monopulse seeker can accomplish HOJ. These include:

R-23/24R (AA-7 Apex),

R-27R (AA-10 Alamo),

RVV-AE (AA-12 Adder),

AIM-7M Sparrow III and

AIM-120 AMRAAM.

 

Most other missiles use some form of conical scan seeker, that is generally more vulnerable to modulated ECM.

 

It gets more complicated than that though. For example, the older AIM-7F uses a conical scan seeker, but still retains some HOJ capability against simple "pure noise" jamming. Meanwhile the R-23R has a monopulse seeker, but can be defeated with somewhat more sophisticated velocity gate pull-off (VGPO) deception jamming (DECM). The Su-27's Sorbtsiya jammer features a "terrain bounce" method that may work even against monopulse seekers - at least at low altitude over water, where surface reflections are high.

 

"Burn-through" itself is a term from Vietnam, that applies more to standoff jamming (e.g. B-52s in a "cell" providing mutual coverage for each other) involving command-guided missile systems like the SA-2, in which the missile doesn't actually carry a homing seeker at all, and all the ECCM takes place at the ground radar. What it refers to is the moment when the jamming from a single aircraft can be distinguished from the jamming of the other aircraft in the group - allowing that single aircraft to be targeted in angle. Even in this case, the range to the target is still unknown, hidden by the target's own jamming.

 

Cheers,

 

-SK

[tflash]

"When the missle gets close enough, and burns through, it then can acquire the bandit on its own, and make the HOJ kill. "

 

That would be for an ARH missile, in the case of SAHR missile it will be the launching aircraft's radar that burns through.

 

In fact, when you bring it back to it simplest form, noise jamming simply adds background noise so that the signal-to-noise ratio is seriously degraded.

 

However!

 

- The power of jamming decreases less with distance since it travels only in one direction; inversely this means that the nearer you get, the faster the signal-to-noise ratio is getting better and you will meet the burnthrough point where the echo is 8-12 dB higher than the jamming signal. (ok, everyone knows Stimson's standard work on the matter)

 

- since the jamming signal only travels one way AND is designed to overpower an emitted signal that has to be able to travel back, you can detect it necessarily from farther than your own radar's reach: it's like a beacon.

 

- since noise jamming essentially hides to the radar what is behind the jammer, it is most useful, in this simple form, to get a strike package through an air defense layer. It works best to hide the true number of aircraft.

 

- in an air-to-air context like Lockon you are most of the time just giving away your presence. A good tactic could be just to use it in an engagement, delaying an adversary lock to be able to get the first shot. HOJ reduces the timeframe in which this tactic is useful.

 

I guess, if you use teamspeak and one of you has its radar off, intelligent use of jamming can bring an element of surprise.