WIRELESS II THE HOME.

Otago Witness, Issue 3584, 21 November 1922, Page 60

WIRELESS II THE HOME.

By Dn Lee de Forest, iti.d., Sc.d. the condenser. We will now take up the Condenser. Condensers for ns© in receivin', sets are of two types—Fixed and Variable. They have what is termed “eupacit-v.”—i.e., just a.s a jar has a certain capacity for containing water, so a condenser will contain a definite amount of electricity A.s the name implies, the capacity of a" Fixed condenser is definite and unchangeable, but the ear:;i< ity of a variable condenser may be changed as well. Figure 9 shows, diagrammatical l !*, the construction of a, fixed condenser, although mi; a is now used instead of paper and sheet copper is preferable to tinfoil. As will be noted, fire sheets of tin foil are

shown, all separated from each other by the paper, Wheels one, three and five all project beyond the' paper at the right and are connected together. Sheets two and four project at the left, and are connected together. The pile is then clamped tightly together and is ready for use. in Figure 10, we have an illustration of a variable condenser. Semi-circular plates of aluminium are mounted on three pillars and separated about t> inch by

small washers. Another battery of semicircular plates, slightly smaller in size are mounted on a shaft and also separated s inch. The two groups of plates are then fastened in such relation to each other that the plates of the second group can be swung ’between the plates of the first group but not touching them. The knob and pointer shown are connected to the shaft of group two, and turning the knob to the right swings this group in between .the plattg of the first group, so varying

I the capacity. Ihe ileneycomb Tuning ( oil described before, enables an operator to vary his circuit so that it is responsive to incoming signals, hut this “tuning’’ is not .sufficiently accurate or “fine,” so a Variable Condenser is used to secure a more precise degree of accuracy and to enable the operator to hear even very weak signals. When the single layer, movable contact type of tuning coil is used, a Fixed Condenser is employed in the circuit. THE HEAD TELEPHONES. Ihe purpose of the head telephone receivers as shown in Figure 11 is to change the varying direct- current impulses ut tiie receiving circuit to sound waves. I here must then, be two distinct parts in ■i receiver; one that will be affected by the impulses and affect the other part that will, in turn, affect the air and cause it to vibrate at audible frequencies. If

a piece of soft iron is surrounded bv a coil of wire, and current is caused to flow in the wire, the iron will become more

or less magnetic as larger or smaller current is applied. In a head receiver then, we find two pieces of soft iron, each surrounded by a coil of fine wire, the coils being connected to each other and th 6 receiving circuit. As the impulses caused by tiie incoming signals vary, being stronger or weaker, the magnetic strength of the iron cores varies proportionately. Mounted very close to, but not touching, the -ends of these cores is a round, thin, springy disc or metal containing iron, the centre of which is attracted to the cores to a greater or lesser degree as the impulses vary. This springy disc, called the diaphragm, acts on the air in contact with it and as*it bends toward and away from the magnets within the receiver, creates vibrations of the atmosphere at a frequency per second that is audible.