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Oral History of Defence Electronics
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ECM Changes.

By Phil Rowe USAF (retired).


When I started in the electronic warfare or electronic countermeasures (ECM) business, back in the 1950's, the equipment and tactics were similar to those used in late WWII and the Korean War.

We had simple noise jammers that had to be tuned manually to coincide with enemy radar signals. We had transmitter systems like the APT-1 and APT-5. Our receivers were old too, like the APR-4 and 4Y, though the APR-9 was soon added. The ability to "see" what was happening in the radio frequency spectrum was provided by the panoramic adaptor, really for seeing the intermediate frequency (IF) portion of the receiver.

Advances in ground and airborne radar systems brought correspondingly advanced ECM equipment and new techniques. But the basic philosophy was to deny the enemy knowledge of your position, altitude, course and numbers. We had countermeasures for early warning and long range radars, as well as some rudimentary techniques for protecting against tracking radars, ground and airborne.

Multiple frequency radars, and those that could shift frequencies to avoid jamming, made the ECM operator's job more difficult. The advent of moving target indicator (MTI) systems and signal processing made chaff all but useless, except for its general nuisance value.

The biggest thing multiple frequencies and frequency shifting did was make jamming more complex. Keeping a jamming signal frequency-coincident with the source radar became more challenging. Available jamming power had to be spread broadly or shifted from frequency to frequency with agility and accuracy. That was a tall order. Simple noise jamming techniques became less reliable.

We used terminology descriptive of the techniques. Spot jamming was simply putting one jammer signal at the same frequency as the enemy radar, one signal at a time. The name probably resulted from the "spot" in the spectrum that we were jamming. Barrage jamming was the technique of simultaneously jamming over a range of frequencies. It was problematical because available transmitter power had to be spread. You didn't put all available power onto one signal.

And sweep jamming was a kind of compromise between spot and barrage techniques. Sweep jamming involved automatic shifting over a range of frequencies in an attempt to put all available power into the bands requiring it. This was marginally effective because it was difficult to put the jamming exactly where it was needed at the proper time and frequency. Jamming was getting very complex.

Arguments developed among strategists and tacticians about what countermeasures to use at all. Some advocated denying the enemy all information about aircraft position, course and altitude, at the very earliest chances of encounter. That meant having the capability to jam both long range early warning radars and ground control intercept (GCI) management radars which could vector fighters at our bombers.

Opponents of that philosophy argued that you could not really do that in the first place, because multiple radars could simply triangulate on your jamming signals. Even if individual radars being jammed couldn't see your echoes through the noise, they could certainly take bearings on you and with bearings from other radars quickly locate your position. While they could soon establish your course, they still might not know your altitude. The use of low level flying, to deny enemy radars early indications of incoming planes, was also proposed, though navigational problems had to be overcome before that was practical.

Some advocated not worrying about early warning and GCI radar networks. They argued that nobody was ever shot down by those radar systems. What was really important were the so-called terminal threats. A fighter's airborne radar that could acquire, lock on and track you was a terminal threat. So too was a surface to air missile system that could do the same thing. It was these terminal threats that deserved attention. Since you could never really deny the enemy knowledge of your presence, what you should concentrate on was terminal threats.

The B-58 was the first aircraft that I knew that had ECM systems solely devoted to terminal threats. My days in B-52's included attempting to master the techniques of countering both early warning and eventual terminal threats. But now, in B-58's, we adopted a wholly new philosophy and set of ECM equipment. Now we would concentrate exclusively on jamming those systems which posed actual dangers of terminal encounters. That included airborne radars in fighters ( and some missiles ) as well as surface to air missile systems (SAM's).

Our B-58 ECM receivers and jammers were quite different from those I'd known in B-52's. No longer was I surrounded by a variety of receivers, panoramic adaptor scopes, multiple jamming transmitters and such. Now all I had was a multi-purpose radar warning receiver and a pair of automatic transmitters. Those transmitters were pre-programmed to jam enemy radars, according to general types and characteristics. Knowing whether or not they were working and effective was a mystery, for all you had was an idiot light to tell you they were ON or OFF.

Techniques of terminal radar countermeasures became highly sophisticated. Some automatic jamming modes attempted to fool enemy radars by creating false echoes or using delaying techniques to alter the spatial position your aircraft echo would present on the operator's scope and equipment. Techniques like side-lobe jamming and delayed transponder or repeater jamming were introduced. All depended upon solid knowledge of enemy radar characteristics and good electronic intelligence. We were never quite sure those fully automatic terminal jamming systems would work.

We still carried chaff, those tinsel-like bits of metalized foil, to drop when needed. The only problem was knowing just when and how to drop the chaff. Our APR-12 radar warning receiver was of dubious value at times. The tacticians came up with a variety of schemes to help us combine radar jamming, chaff drops and evasive maneuvers to counter threat systems. Some were pretty wild and off-the-wall.

To make life more interesting and challenging for ECM operators, the advent of infrared (IR) threats and countermeasures evolved. This entry of threats in the higher realm of the electromagnetic frequency spectrum was revolutionary. Now we had to worry about heat seeking guidance systems that could direct air-to-air or surface-to-air missiles against us. Such systems could find and track us without warning, for radars were not always necessary.

To counter IR systems we began to carry IR decoys, flares, which could be used to fool the guidance systems of incoming missiles. The problem was one of knowing when and how to deploy the flares. Unless you got clues from other sources, radar warning receivers, you might not know that a heat seeking missile was headed your way.

Efforts were made to develop IR receivers which would alert crews of a missile launch. The rocket plume of a surface-launched or air-launched missile could be detected, under some conditions. That might provide warning to crews that something bad was about to happen, but it was precious little information to base actions and countermeasures upon. Life was getting worse for ECM operators.

I wish I could reassure readers that all is well in hand. I wish I could say that we have advanced to the place where we always know exactly what threats are out there, how they are being used and countermeasures were effective. It just isn't so. There will always be threats to aircrews and ECM will always play catch-up in the war of measures and counter-measures.

That's what makes it so interesting. But it is also deadly, more complex and ever so much more expensive.



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