Radio Broadcast (May-Oct 1922)

4^2 Radio Broadcast expected, and probably the best results are obtained when the old-fashioned "tube-andknob" wiring has been installed. One side of the house wiring system is generally grounded to the water pipe where the wires come into the house; evidently using such a wire for an antenna will prove rather futile. The ungrounded side of the wiring system is the one which should be used to pick up the radio signal, but this wire must not be connected directly to the receiving set as a short circuit is almost sure to result, burning out house fuses and quite likely damaging the radio set. The special plugs sold for the purpose of using the lighting wires for antennas are fitted with condensers which will let through whatever radio currents there may be on the wires and still prevent the lighting current from leaking to ground and damaging the apparatus. The plugs sometimes used for this purpose have cheap paper condensers in them, which may or may not give sufficient protection from the lighting current; only those plugs which have been subjected to a high voltage test should be used. In tests recently conducted in New York City, where the wiring was all underground, the signal received was poor, and much disturbing noise, evidently originating in the motors used in neighboring factories, was encountered. But the same power system gave fairly good results, fair signal and but little disturbing noises, in the outlying parts of the system, where the wiring was overhead and there was no machinery operating in the vicinity. When a signal is received from an underground system the effect is due to the fact that radio waves do penetrate a conducting medium to a certain extent; this penetration of the waves into the earth is not mysterious but might be calculated if the local conditions were exactly known. It is this earth penetration which accounts for the success of the Rogers underground antennas as described in our August number. ELIMINATING "a" AND "b" BATTERIES BY GETTING POWER FROM THE LAMP SOCKET SOME months ago there appeared a notice that the physicists of the Bureau of Standards were ready to hand over to the radio public a wonderful boon in the shape of a triode amplifier which required no batteries of any kind for its operation. To many of us whose enjoyment of a concert has been spoiled by the sudden giving out of the filament storage battery, or who have been bothered by noisy, loose connections or bad cells in the plate battery, this announcement was indeed welcome. The interest of the public in the new device was so great that the Bureau had to get out a form reply to the numerous inquiries as to how soon the description of this battery-less amplifier would be ready. In the July number of the Journal of the A.l.E.E. there is an interesting description of this amplifier by Physicist Lowell, of the Bureau, who has done the major part of the development work in the perfection of the new apparatus. The article shows the growth of the idea from a simple threetube arrangement to the final product, which has the Bureau's seal of approval, an amplifier and rectifier outfit using altogether seven tubes and a crystal rectifier. Three tubes are used to make a radiofrequency amplifier feeding into a crystal detector circuit, which changes the modulated high-frequency current into an audio frequency current; from this crystal circuit the current passes through two stages of low-frequency amplification into a loud speaker. The filaments of all tubes are supplied with power from the secondary of a specially wound transformer, the primary of which draws its power from the ordinary sixty-cycle alternating current supply available in the average home. One rectifier tube, in combination with choke coils and condensers suitably connected supplies plate current for all the tubes and the other rectifier tube supplies the current used to excite the magnetic field of the loud speaker used. The latter tube is of the gas-filled variety, the Tungar tube used in small storage battery charging outfits. This type of tube, by the way, is a direct outgrowth of the Hewitt mercury arc rectifier, the source of electrons being a hot filament instead of the hot spot in the pool of mercury as used in Hewitt's rectifier. The transformer and rectifier tubes are conveniently mounted in one box and the five-tube amplifier unit is compactly arranged in another; in order to make the amplifier operate it is necessary only to connect the flexible cord in the ordinary lamp socket. The amount of power drawn from the house circuit is about