The Birmingham age-herald., 1922-09-17
BROADCAST MADE POSSIBLE BY USE
 OF VACUUM TUBE
Steam Engine Analogy Shows How It Gives Off the Oscillations Needed to
 Produce Carrier Waves
Bx JACK BTyNs

great deal of the progress that nas been made in the broadcassing and reception of music and speech by radio Ia dependent upon the fact Hhat three-electrods vacuum tube Is capable of generating what Is known as an oscillating current. This oscillating current consists primarily of a direct current, the rate of flow of which is periodically Increased and decreased. It must not be confused with alternating eurrent. such as is used in many parts of the city to operate the electric lighting systems. Alternating current flows in one direction for part of its cycle and then changes direction completely. Such re- iversal of current in the vacuum tube is Impossible, due to It's valyelike character. since 1t permits & flow an one direction only.
 The oscillatory characteristics of the three -electrode vacuum tube have been Of great value in produc- Ing the extremely high frequency carrier currents that create the cleo tro-magnetic waves radiated from a broadcasting station. These waves are the carriers that transfer music and speech through space to the aer- ials of the>receiving sets by changes in their successive amplitudes cor responding to variations in the tone impressed upon the transmitter at the broadcasting station.
 When we speak of a 360-meter wave we mean that the electro mag hetie impulses are being propagated at the rate of almost a million second. The problem of constructing a rotating machine to generate an alternating current of this frequen- cy is prodigious and the three-elec- trode vacuum tube is an expedient s which performs the task in simple manner.
 Aids Continuous Wave Reception
 The highly selective and efficient hetrodyne system of continuous wave code reception Is another ex- ample of the oscillating tubes apph- cation. By super-imposing the os- cjllations of local circuit upon those of the incoming signal, 1t was found possible to produce a result ant oscillation of a frequency that was within the range of hearing. Those who have operated regen- erative receiving set have no doubt heard the musical note of contlnu ous wave signals and have founu that the pitch changes considerably with the SllBnItSl NOhANAN oA
 Tuning handles of their set. In this ease the receiving set Is producing | the local oscillations necessary to / give audibility and the change In njteh is caused by a variation in the Freouency of these local oscillations.
 Provided regenerative set IS properly constructed 1t is capaple or prodncing oscillations As the tick Ter is moved toward the tuning CIT cuit it is common experience that inc music or speech will be ampu- fled until at a certain point squeai sets in. Further movement or the ticlxler results in a complete drown inc ont of the incoming signal, and if the operator wishes 10 keep on sneaking terms with his neighpor, who has an aerial near by, he had better decrease the ticker coupling nromptly. The squeal means that inc tube is oscillating and under these conditions the receiving set be- comes a low-power broadcastlns stat.on with nothing on It's program except noise.
 Cured Inv Dose of Same Poison
 Tn the super -regenerative circuit recently introduced by Major Arm strong. the oscillating tube IS put to a new and unique task. By thrott1ing the tendency of one tuoe to oscfllate with the oscillations gen erated by another tube, this circuit makes use of much closer ticker coupling, and consequently far great CT signal amplification, than was possible with the original regenera- five circuit Thus an effective anti 6ote has. in the case of the regen- erative circuit, proved to De prop erly administered dose of Its own "poison." ,so
 The grid of the three-electrode vacnun tube acts somewhat as the trigger of a gun releasing at com paratively small expenditure of en, ergy a surge of elestrons toward tbe niate surface positive charge electrical charges and since the plate Is charged positively by connecting The plus side of the B battery 10 IL