Radio broadcast .. (1922-30)

RADIO BROADCAST into the sets with a number of tuning knobs, because good tuning does call for a number of tuning members. There is no such thing as simplicity combined with utmost efficiency in radio reception. Good tuning can only be obtained with a number of controls. Another point to bear in mind is that the most important development in radio reception has been the introduction of the regenerative scheme invented by a radio engineer named E. H. Armstrong. To go into details concerning the Armstrong scheme is virtually impossible in this limited space, and a description of his invention was published in the last issue of RADIO BROADCAST; but suffice it to state that the Armstrong regenerative scheme simply converts part of the battery energy into oscillatory energy which is added to the incoming wave energy, giving greater strength to the ultimate sounds heard in the telephone receivers. Thus the detector is not only a detector but an amplifier as well. So in purchasing a vacuum tube receiving set it is well to find out whether or not it is a regenerative set. Other vacuum tube sets will give good results, but the regenerative arrangement makes for greater range and louder signals with little more complication. The simplest regenerative receiving set selling for $75.00 will cover a distance of 75 to 100 miles under normal conditions, with a good antenna. For shorter distances it will give exceptionally loud signals, and will permit of using a number of pairs of telephone receivers. For distances above one hundred miles, it is necessary to use the more elaborate kinds of receiving sets of the regenerative design, together with what is known as the amplifier. The amplifier may be included in a given receiving set, or it may be a separate piece of equipment. The amplifier increases the strength of the sounds heard in the telephone receivers, and thus brings up weak sounds, due to weak waves, to full audibility. It also makes possible the building up of weak sounds until they have attained sufficient volume to operate a loud-speaking horn, so that the music or speech can be thrown out in a large room and used for church, club, home entertaintment or dance purposes. Amplifiers come in the one-stage and twostage models, and sometimes in the three-stage model, although the last-mentioned type becomes somewhat too complicated in its opera tion for the average amateur. The one-stage amplifier builds up the sounds to about four or five times their normal strength, while the second stage builds up this amplified energy four or five times more, or sixteen to twentyfive times the normal strength. Hence it will be noted' that the amplifier not only gives louder sounds, but it also increases the range of the receiving set not a little by making what would hardly be audible sounds fully audible and even loud. So the amplifier is necessary when operating over a distance of more than 100 miles. For 200 miles or more a two-stage amplifier is absolutely necessary. The usual type of amplifier is known as the audio-frequency type, because it handles the sounds or the currents of audible frequency which have come through from the detector of the receiving set. There is another type of amplifier known as the radio-frequency type, which is just coming into limited use. This type handles radio-frequency current, or current representing the radio wave energy, and builds up such current before passing it to the detector, which converts it into audio-fre < quency current. The radio-frequency amplifier, which comes in one-stage, two-stage, and even three-stage combinations, builds up the intercepted wave energy and not the sound strength. It makes for remarkable sensitiveness and for the covering of great distances, but it remains for the audio-frequency amplifier to give loud sounds. Often the two types I of amplifier are included in one receiving outfit. In cases where an antenna of the proper size cannot be used, then resort must be had to an improvised antenna. Anything will do j to intercept radio waves at a reasonable distance. Thus a single piece of magnet wire, as insulated wire of small sizes is called, may be placed about a room behind a picture moulding. A piece of wire some forty feet long, concealed and out of the way, is sufficient to receive broadcasted programmes over a distance of 50 to 100 miles with a good receiving set with two-stage amplifier. The same set with a good antenna, however, would cover a distance of many hundred miles. Distance must be sacrificed with such improvisations. It is only a matter of time when antennae will be done away with in most amateur radio reception, and the so-called loop will be employed. This consists of nothing more for }