INTRODUCCIÓ

Not surprisingly, assimilating all this switchology is a task which takes the best part of a year, even for more experienced flyers entering the F-15E programme.

Most F-15Es require over 320 hours annually.

Incoming crewmen need 20+ hours a month which compares favourably with many dedicated INT aviators. Given this requirement, the F-15E arrived on the scene barely in time for Desert Storm: the first operational Wing to form, the 4th TFW, began working-up from late 1989 and went into combat just over a year later.

Their chief accomplishments were the proving of the potency of LANTIRN and the SAR radar, and the type's massive growth potential as a missile launch platform for anti-Scud tasks. It also demonstrated its

TARGET INGRESS

Russia's counterpart to the Raven is the Su-24MR Fencer strike-recce, jamming and Elint platform. Unlike the Raven, this aircraft boasts provisions to carry a pair of R-60 rockets (AAMs). (Ka'Roly Gere via Ga'bor.

Szekeres)

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potential as a prospective leading component of future SEAD. But they actually spent the best part of their time dropping LGBs in much the same manner as the F-lllFs had been doing for years. And only after Desert Storm were they qualified to use some of the new smart weapons such as Deep Throat and the GBU-15/AGM-130.

If we are to refocus on the F-111, albeit briefly, then it is because of its vital ancillary role as support EW platform in the guise of the EF-111A Raven. This fights a seemingly silent but nevertheless vicious electromagnetic battle. While all the pounding and exchanges of missiles takes place, numerous EW support aircraft are lurking offstage to provide warning of enemy activity (an ancillary function of the AWACS and Rivet Joint sentinels) and what is termed soft kill SEAD or jamming. The 18 EF-111A Ravens assigned to Taif near Mecca proved crucial to the successful outcome of the 42-day-long air war against Iraq and Occupied Kuwait. Their sole armament comprised electrons fired at the speed of light - a mission the crews referred to as 'Rockin' Iraq' in deference to the electronic 'music' they played.

The heart of this ostensibly passive EW fighter is its 3 tons of receiver and jamming equipment, collectively referred to as the Grumman/Eaton AIL AN/ALQ-99E electronic jamming system (EJS). The receptive part of this, the system integrated receiver (SIR), is contained in the 'football' mounted on top of the fin. In concert with additional receivers built into the nose, the SIR sweeps through preselected frequencies in the A-J Bands (around 0.1 to 10.5 gigahertz), listening for potentially hostile radar emissions contained in its constantly reprogrammed computer threat library. With only minor intervention from the right-seat EWO, who can review the threats on a DDI, the system then responds with finely tuned spot-noise jamming. This is directed right at the relevant threat(s) by means of a bank of 10 steerable antennae driven by powerful 1,000 Watt exciters, contained behind a 'canoe' on the underside of the Raven. Engine-mounted 90 kW electrical generators ensure adequate power reserves for the job.

The system is carefully arranged so that it can work in look-through mode. The Raven can listen and jam simultaneously, with little risk of electromagnetic interference to itself, the Wild Weasels, or even Allied AWACSs and other friendlies, which might otherwise be swamped by all the noisy signals. This is made possible by using selective spot bursts, often of very short duration, carefully tuned to the operating frequencies of the enemy radars. The net product is to white out the enemy's radar screens or clog-up their automatic gain receivers (AGCs), making it virtually

impossible for them to acquire airborne targets. Air-to-air fighters also can be thus hindered in their attempts to acquire their trade.

The Raven flies three distinct missions, whereby enemy radars assume different priorities in the threat hierarchy. Stand-off is the relatively safe mission assignment. It involves two or three Ravens orbiting in racetrack patterns at up to 50 miles behind the FLOT at 15,000-20,000 ft with their wings spread-eagled at 16° for maximum cruise economy. They loiter for up to 4 hours at a stretch. Between them they put out a maximum jam footprint to generate an electronic smokescreen to obscure the position of strike packages ingressing and egressing enemy first tier defences, as well as to help conceal backstage AWACSs, GLOBs and other support machines.

Close-in tasks a solo jet or pair of Ravens close to the FLOT at more discreet altitudes of around 500 ft AGL, to support 'mud-movers' engaged in CAS or Special Operations work. The task is to shelter them from all but the E-0-guided devices and small-arms fire, which they must take care of themselves. It should be pointed out here that these tasks can also be performed by the USN/USMC Grumman EA-6B Prowler, a stretched, four-man version of the A-6 Intruder equipped with the EJS. It also specializes in communications-jamming (comjam) and covert ESM listening duties, often with a language expert sitting in one of the three Electronic Countermeasures Officer (ECMO) positions.

The American penchant for developing sophisticated EW machines has been matched only by the former USSR. Russia still boasts an impressive array of tactical jamming aircraft capable of conducting deep strike, including the still novel-looking Yak-28 Brewer (being phased out), 17UM-3K Fitter, and the Aardvark-look-alike the Su-24MR Fencer F. All may be outfitted with jamming and Elint pods. Very little is known about their true capabilities, but suffice it to say that the CIS is highly skilled in the art of EW jamming and has a clearly defined penchant for the esoteric. However, cruder avionics fabricalion methods, which still lag behind the West, probably limit capabilities to blanket-noise jamming, without look-through as an option. In other words, they head straight into the thick of it radiating power in large bursts, possibly without regard to what effects it might have on their colleagues!

What makes the Raven unique is its third mission category, made possible by its earth-hugging transonic performance: primary. This frags between four and six crews on deep strike escort assignments way behind enemy lines. A pair of Ravens may precede, accompany or even trail behind a loosely knit strike package. They stay low in TFR mode and pop up to

TARGET INGRESS 157 500 ft or higher for brief bursts of radar-jamming

activity to cover colleagues during the heat of a bombing run, or when a particular threat breaks out on the airwaves. It should be pointed out here that the spot-noise jamming undertaken by the Raven during stand-off and escort missions is mostly performed against early warning, height-finder and SAM acquisition radars working in the lower-frequency bands. Primary mission extends the tasking to the higher-band terminal guidance threats. These are tracking and illumination radars used to actually guide SAMs and flak to their targets. The mobility and frequency-agility of these devices makes it a tough assignment. Crews must learn how to work decisively in a time-compressed high-threat environment where EMI can all too easily become a problem. And enemy jamming (designed to swamp attack radars and even jam TFRs) and decoys (luring the Raven into a trap) pose a real threat.

Improvements to the EJS's software is virtually continuous. Hardware updates under the Systems Improvement Program (SIP) are being developed by Northrop Grumman. These are intended to massively improve its electronic jamming reflexes: an astonishing 100-fold increase in threat tracking with jamming response-time halved, keeping the Raven viable through to the year 2017 when the airframe's 8,000-hour fatigue life will be exhausted.

While retention is subject to the whims of higher authority (the Ravens might be axed alongside the F-UlEAMPandF-lllFforceattheendofthedecade), the sleek ghost machines remain crucial in supporting non-stealthy strike aircraft. These will continue to make up three-quarters of American air power, and a greater percentage of that of their allies whom the Ravens regularly support, well into the next century.

But contrary to official propaganda, they are essential to stealth survivability too. There were many subtle tactics used during the Gulf War. Some of the F-117A Nighthawk's extraordinary survivability can be directly attributed to Ravens. They got Iraqi flak batteries to blaze away in the midst of jamming which the Iraqis believed was intended to mask Coalition strike machines - effectively causing the gunners to overheat their gun barrels with indiscriminate fire. In fact, it was timed a quarter of an hour prior to the Nighthawks' TOTs! By the time the guns had cooled down sufficiently to be fired again, the Nighthawks had long since dropped their bombs within strict 30-second 'gates' and had sped south-west!

Ultimately, however, the EF-111A force can only be spread so far in combat. With 30 of the 40 surviving airframes available for operations, only half of which can realistically be airborne at any one time, fighter crews need to exercise a good deal of self-reliance and

use their own strap-on or internal ECM equipment in a crisis. By the time a missile is on its way, or a line of flak is being radar-walked to a fighter, reaction measures give no leeway to call up a Raven and cry for help!

Self-protect systems are truly multifarious, comprising the great circus parade of American ALQ (airborne countermeasures, special-purpose) hardware produced by ITT, Loral, Northrop, Sanders and Westinghouse, and their European equivalents which bear code-names such as Barem, Barex, Rapport, Rémora and Sky Shadow. Backing them up are the expendables, chiefly chaff and flare ALE (airborne countermeasures, expendable) devices, but there are also some newer weird and wonderful throwaways. In describing how these systems negate the enemy's missiles and flak it is necessary to go back to basics.

While the first indication of imminent danger may comprise nasty flashes of AAA with tracer holding uncomfortably steady in a crew's peripheral vision, or the flicker of a rocket plume from a missile, the chances are that the RWR will light up first. We have already aired this device in the context of SEAD. To reiterate, most fighters are studded with spiral receivers which pick up radar activity in the 0.5-12 GHz frequency range. They process the threat signals into suitable alphanumerics on small dartboard-like crystal video displays located in the cockpit. Range and bearing is shown relative to the target aircraft (which is denoted by the centre or bull's-eye in the display) by the symbol's relative position. The type of threat is denoted by its annotation: ' 12' for an SA-12 Gladiator SAM, an inverted 'V for an enemy fighter, 'A' for triple-A, and so on. If they start flashing, and the warble warning sounds over the earphones rise in intensity, then that radar type is guiding anti-aircraft weaponry. Time to 'get the pod, and hit the chaff/flares'.

There are some variations on the RWR theme. For example, the Russian MiG-23's Sirena 3-M and newer MiG-29's Beryoza SPO-15 RWRs work on concentric coloured lights. The outer row of yellow show priority threats by type, and the inner green ones their bearing.

The L-150 Pastel derivative works in a similar fashion to the F-16C-HTS. It is able to cue ARMs as well as activate countermeasures. However, the philosophy remains the same: hit the countermeasures buttons!

First, let us deal with the pods (or internal) radar ECM suite.

In common with many other systems aboard the aircraft, the ECM switchology has been simplified to 'on' and 'off' (with minor subtleties such as Mode A, Mode B, etc). In reality, the devices operate using a number of well-established theoretical techniques

which can be roughly divided into noise jamming, and track-breaking (deception). Noise-jamming works much like that generated by the EF-111A Raven to fog enemy radar screens and overload AGCs, but is less selective and not so powerful. It is usually preset on the ground prior to take-off, although more sophisticated jammers can respond with signal noise

tailored to the threat on the basis of signals received by the RWR (for example, the Westinghouse AN/ALQ-101(V)-10, which remains in use on board RAF Jaguars).

This technique usually works best when the aircraft is part of a formation. Several aircraft can white out a sector on the enemy radarscope (or its

Fooling a conical-scan radar and related SAMs, first with ECM. 1 The aircraft's receiving systems listen to and analyse the enemy radar emissions so that onboard ECM can subsequently respond with convincing fake echoes (i.e. the same frequency and pattern). 2 The ECM replies with modulated output. When the radar beam is off the aircraft at point X (as depicted) the pod sends out strong fake echoes, and when the beam is on or near the aircraft at point Y, weak or non-existent signals are transmitted by the ECM. This modulated output is repeated over several conical scans. 3 The radar dish now swings its axis over to scan the sky around point X, believing the aircraft to be there. It has now been 'walked off' the aircraft which will disappear from the radarscope. 4 Simultaneously, on receipt of a SAM launch warning chaff is released which blossoms into a distracting cloud at point Z aft of the aircraft. 5 The reflective cloud overdrives the enemy radar automatic gain control, and the dish now swings its axis over to scan the sky around point Z. Command-guided SAMs and radar-directed AAA are directed onto this spot, out of harm's reach, while semi-active radar-homing missiles will similarly be attracted to the radar-painted chaff cloud. Active and towed decoys could also be used with similar results. 6 As a final measure, flares are released. Infrared heat-seeking missiles (or radar-guided ones with terminal IR guidance) may not befooled by the chaff or jamming pods, so a gaggle of strong-burning sources is used to lure them away

TARGET INGRESS 159 AGC brains) or create a superblob on the display. Flak

and SAMs usually then wind up off the mark, or pass at mid-point, between the aircraft. When used in this fashion, it is a perverse form of countermeasure as it first actually advertises the Flight's position, and then merely aims to make the job of tracking individual aircraft tough. By and large, this approach remains a switch-on-and-leave-on one which lacks the necessary frequency agility to cope with today's more sophisticated tracking radars. And the system breaks down completely when the aircraft depart from their canned formation spreads.

Far better are the track-breakers, which actually generate spoof targets or even cause the enemy radar to break lock altogether. Amongst these devices are the Northrop Grumman AN/ALQ-135 built into the F-15E Eagle DRF, and the F-4G Wild Weasel's external Raytheon AN/ALQ-184 pod. This uses Rotmen lenses - fan-like transmitter arrays - which can direct the jamming power to increase effective radiated power (ERP) by an order of magnitude by electronically focusing the jamming at the chosen threat. Still, the actual signals need to be properly matched to be effective and the techniques used with deception jamming are complex. By and large, they fall into two distinct subcategories, which use frequency-modulated or amplitude-modulated techniques, with the ECM responding automatically when switched on. These systems can usually cope with up to 30 different wave forms spread out over two or three bands.

The first is Range Deception or the Transponder Mode. By taking in the enemy radar pulses, analysing them and then transmitting them back at the radar alongside the echoes, the enemy radar's AGC will more often than not lock on to the ECM signals, as these are stronger and clearer. Once the AGC has locked on to the ECM signals and has begun to ignore the true returns, 'all' that is required is to gradually introduce a time delay between receiving a radar pulse and transmitting back a spurious echo, and increase it.

As time of return relates to aircraft range, the increasing delay in the echoes put out by the jammer causes the radar computer to believe that the aircraft is further away than it actually is, throwing SAM and AAA lead-firing angles off the quarry.

False azimuth and elevation data can be generated by getting the pod to reply out of phase. This is especially effective against conical-scan radars which use a narrow beam which quickly and repeatedly scans a tract of sky. Their echoes are strong when the beam hits the aircraft, and non-existent when it misses.

So, as the whole radar dish turns towards the last known position of the aircraft, as indicated by the strongest echo, repeater mode signals, matching the

radar's output but out of phase with it, can be used to throw it off whack. This works because the ECM signals copy the radar signals but are phased so that when the beam is off the aircraft the ECM transmits strong fake echoes, and when it hits the aircraft (the AGC already having locked-on to the jammer's signals), weak signals are dispatched. The whole radar dish then tends to swivel onto the point in the sky it was looking at when the strong fake returns were received, thus walking it off the target. Over a period of scans - a process conducted in a matter of seconds or less - the enemy guns should be shooting at clouds with SAMs fired off in the wrong direction in pursuit of elusive prey. More complex modulation techniques are required to defeat Doppler and coherent radars.

Frequency modulation is used to give false closure rates and false ranges. Modern jamming number-crunching is often surprisingly good at the job.

However, the radar might not be fooled sufficiently to adequately misdirect a SAM which is using infrared terminal homing to catch its quarry. It is here that the chaff and flares come into play, released rapidly as individual cartridges through slots in the dispensers, most of which resemble ice-cube trays. Crews often preselect the rate of release - say, six flares every 2 seconds - or leave the system to work autonomously at full speed on hitting the 'go' knob.

Fundamentally, the chaff cartridges provide a radar-reflective cloud which obscures the target's position by swamping the hunter's radar with false returns. There are hundreds of strips of aluminium or metal-coated plastic ('tinsel') in each cartridge, precut to suitable dipole lengths (quarter wavelengths of most anticipated radar threats). This makes them far more convincing as fake echoes on radar. By simply churning out a sufficient quantity, it is likely that the radar will be fooled into thinking that at least part of the cloud is a target, and will break lock from the

Fundamentally, the chaff cartridges provide a radar-reflective cloud which obscures the target's position by swamping the hunter's radar with false returns. There are hundreds of strips of aluminium or metal-coated plastic ('tinsel') in each cartridge, precut to suitable dipole lengths (quarter wavelengths of most anticipated radar threats). This makes them far more convincing as fake echoes on radar. By simply churning out a sufficient quantity, it is likely that the radar will be fooled into thinking that at least part of the cloud is a target, and will break lock from the