Radio broadcast .. (1922-30)

The Choice of a Receiving Tube 287 point X. (While, of course, it travels out from this point in all directions we are only considering its easterly bearing.) At first, it falls off very quickly and passes below the line IK at M. This means that the distance IM is as far as the signal can be heard at this particular time, on a crystal receiver. It may be ten miles. It may be fifty. The signal continues on at point N, where it falls below the line GH, which represents the amplification limit of the regenerative receiver. This station then, may be received at this particular time with a regenerative receiver at any point between G and N. Now, it may be seen that this signal travels still a great distance before it reaches the point B, where it passes below the static level and is lost to any form of receiver. And here is where the more sensitive set gets in its work; for the set that is capable of giving sufficient amplification to get down below the static level at this particular time, can receive that radio signal anywhere over the distance up to the point B, which in this case we are supposing is practically twice as far as the regenerative receiver will go. Here is a real gain, and it is made possible by one thing only — the low static level of the static interference represented by the line EF. If this line EF were as high as, or higher than, the line GH (as would be the case on almost any summer night), the regenerative receiver would be able to receive over just as great a distance as FIG. 4 A crystal set can receive San Francisco's signal at IM distance from the transmitting station, a regenerative set at GN distance, and a super-heterodyne at any distance up to point B the receiver with unlimited powers of amplification. Therefore, the factor which limits the range of a radio receiver is not only its sensitiveness hut the signal-static ratio. I do not mean to say that this condition will never be overcome. There are already systems of radio telephone broadcasting (such as single side-band transmission), which will improve the signal-static ratio; but with the radio reception and broadcasting we have to-day, this condition certainly does apply and is the fundamental factor that limits our long-distance reception. If the radio fan can realize this, he will no longer complain when on a bad night he can do no better with his neutrodyne or even super-heterodyne than he can do with his old regenerative set. He will realize that, on that particular night, either the signal strength itself has fallen or the static level has risen. The Choice of a Receiving Tube Some Useful Data on Radiotron and Cunningham Tubes By B. S. HAVENS General Electric Company THE choice of a tube to use for a particular purpose depends in general upon three main considerations: i. The purpose for which the set is to be used : a. Broadcast listening for the enjoyment of entertainment programs. b. Experimentation on apparatus and circuits. c. Long-distance code reception. 2. The type of set in which the tube is to be used; that is, the electrical circuits involved, number of tubes used, and whether a loud speaker is included in the equipment. 3. Whether storage batteries, No. 6 dry cells, or flashlight dry cells are to be used for filament operation. THE UV-I99 AND C-2Q9 THESE tubes require a minimum of filament energy. In fact they use only .18 of a watt, or about one eightieth the power consumed by a 4O-watt electric lamp. The bulb is of small size, and a special base and socket suitable for such a small tube are used. On account of the small size of this tube, the capacity between electrodes is lower than in either of the other tubes, but when it is