detection. A countermeasure to ARM is not to use self-protective jamming (one could use stand-off jamming, assuming that the missiles has a range no longer than the radar), or have a decoy taking the missile (such as ADM-160 MALD and AN/ALE-55 Fiber-Optic Towed Decoy). By towing a decoy/jammer, the decoy maintains a realistic Doppler shift (which tricks the tracker) and lures an ARM away from the target. Stealth For protective jamming, a small RCS of the protected aircraft improve the jamming efficiency (higher J/S). A lower RCS also reduce the "burn-through" range. Stealth technologies like radar-absorbent materials can be used to reduce the return of a target. Interference While not usually caused by the enemy, interference can greatly impede the ability of an operator to track. Interference occurs when two radars in relatively close proximity (how close they need to be depends on the power of the radars) are operating on the same frequency. This will cause "running rabbits", a visual phenomenon that can severely clutter up a radar display scope with useless data. Interference is not that common between ground radars, however, because they are not usually placed close enough together. It is more likely that some sort of airborne radar system is inadvertently causing the interference—especially when two or more countries are involved. The interference between airborne radars referred to above can sometimes (usually) be eliminated by frequency-shifting transmitters. The other interference often experienced is between the aircraft's own electronic transmitters, i.e. transponders, being picked up by its radar. This interference is eliminated by suppressing the radar's reception for the duration of the transponder's transmission. Instead of "bright-light" rabbits across the display, one would observe very small black dots. Because the external radar causing the transponder to respond is generally not synchronised with your own radar (i.e. different PRFs [pulse repetition frequency]), these black dots appear randomly across the display and the operator sees through and around them. The returning image may be much larger than the "dot" or "hole", as it has become known, anyway. Keeping the transponder's pulse widths very narrow and mode of operation (single pulse rather than multi-pulse) becomes a crucial factor. The external radar could, in theory, come from an aircraft flying alongside your own, or from space. Another factor often overlooked is to reduce the sensitivity of one's own transponder to external radars; i.e., ensure that the transponder's threshold is high. In