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Esoterics Explained Dear Sir: The questions that have come to me as a result of M. I. Salvati's fine article "Antennas --Part V, Special Antenna Techniques," Audio, Jan., 1979, p. 42, are an indication of your reader's interest in quality FM reception. I only wish we could have supplied more information for your article. The most common question asked us as a result of your article "What is a balun?" was probably the easiest to answer. A balun (for balanced-unbalanced) transformer usually consists of a two-window ferrite core with two windings of four turns each, coupled to provide a balanced-to-unbalanced match and an impedance transformation from 300-ohms balanced (antenna) to 72-ohms unbalanced. Ferrite toroids are used because the decreasing permeability with increasing frequency is offset by the increasing reactance of the wire itself, causing a wideband, flat-frequency response. Although a balanced 300-ohm input is common on tuners, the r.f. amplifier stages are single ended. This means that balun transformer circuitry is used to couple a 300-ohm balanced transmission line to the unbalanced r.f. amplifier. Bryant Arrington, Technical Consultant Long Engineering Co., Winston-Salem, N.C. Ear Fatigue Dear Sir: I have often wondered, after a lengthy plane trip, how much of the after effects of plane travel are due to what is called "jet lag" and how much is simply due to hearing fatigue. Recently I flew to England to see some friends and to compare notes and techniques with Enigma Records recording engineer, Tony Faulkner. On the plane I decided to hire a pair of headphones and watch a movie entitled "The Big Sleep," since if it induced sleep, I would be that much ahead by the time I arrived in London. It was the first time in many years that I had rented a pair of headphones so I examined them with some interest. I found that they were two long pieces of hollow plastic pipe, one ending in each ear. With the usual horrible noise level in our "modern" jet planes, the movie sound track was extremely well modulated by the vibratory jet noise penetrating the cabin . . . so much so, that I shortly discarded the head phones and watched a "silent" movie, after first taking the precaution of chewing up pieces of paper napkin until they were mushy and packing them into my ear canals. Thus, I travelled to London with a minimum of abuse to my hearing and having only a feeling of being shaken by vibration the whole trip. As you should know, our ears were designed for hearing the rustle of leaves in a forest, hearing the murmur of the wind through bare branches, and the soft approach of forest animals, not to withstand the crashing, banging noises of our so-called civilization. Why is it that airplane designers are not aware of the fact that the noise inside the "usual" plane destroys hearing? Couldn't they design a plane in which the outside and inside shells are separated in the same way that a well-designed recording studio is "floated" inside the outside structure? Is it too costly for cheap transportation or is it beyond the scope of the airplane designer's knowledge? Why can't the airlines furnish well-cushioned head phones admitting very little outside noise, together with electrically con ducted sound instead of these present horrors provided to unsuspecting victims? The other day I heard on TV that the head of the CAB was seriously discussing the separation of smokers from non-smokers on planes. Even with is lands of serious drinkers between, separating polluters from non-polluters, doesn't he realize the damage to be done through noise pollution? Doesn't he realize the damage created to the human hearing system and brain by the plane's horrendous noise level concentrated at low frequencies? This noise pollution must be a thou sand times more damaging to humans than the intake of a few milligrams of cigarette, cigar, and pipe tobacco pollutants! -Loel Tall; Washington, D.C. (Audio magazine, May 1979) Also see: = = = = |