Ether's Ack-Ack

With the dogged persistence of antiaircraft batteries blazing away at attacking bombers, Axis radio transmitters are fighting off United Nations' broadcasts with strange and unpleasant noises. When World War II began, Nazi jamming was unpredictable. Today Germany, Italy and Japan all jam regularly, systematically, most of the time.* In spite of their efforts, their jamming is far from 100% effective. The jammer's basic difficulty is that a determined listener can follow a speaker's voice through almost any kind of a din, can grasp the gist of a message even though he hears only a word here & there.

In principle, jamming is as simple as ABC: the jamming station sends out a conflicting broadcast on the same frequency as the offending broadcast. But United Nations broadcasters have various means of fighting back. San Francisco's KGEI sends its programs across the Pacific on at least five different wave lengths, jumps from one to another to evade the Japs. BBC sometimes fights interference by changing its wave length slightly in mid-broadcast; by the time the jamming station catches up to it, it may be on the move again. Furthermore, BBC's European Service at the end of its 16-hour day of broadcasts in 24 languages slowly taps out the news in Morse code (almost jam-proof). Bootleg "freedom" stations leap from one frequency to another, when, where and how they please. They often spend a 15-minute news period repeating four sentences over & over again, confident that if listeners catch an occasional word they will be able to piece the message together like a jigsaw puzzle.

Since total obliteration is well-nigh impossible, accepted jamming practice is to do the next best thing: make such exasperating, excruciating noises that listeners turn to another station rather than be driven nuts. One favorite Axis jamming signal is a series of musical tones repeated interminably, as if a mad vibraphonist were banging away rapidly with one mallet. Another sounds like a collection of piercingly shrill peanut whistles.

The pains taken by the Nazis to jam United Nations' broadcasts is a guide to the willingness of Germans to listen. Some experts guess that perhaps a million Germans still do.

*Russia jams some, Britain and the U.S. not at all, regarding it as better tactics to show no fear of enemy propaganda.

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