The Birmingham age-herald., 1922-06-11
CONDENSER IS IMPORTANT IN
 RADIO SETS
Capacity Is Determined by the Size of PIateS-ThiGkneSS and Nature of
 DieIectric


 There is no individual piece of ap-
 paratus in radio circuits that has so many varied uses as the condenser; and it is. in all probability. the least
 understood instrument in the set by the average user.
 The condenser is divided into two
 distinct types, each of which has a
 specific purpose. They are the fixed
 type and the variable type. In re-
 ceiving circuits, the former inva-
 riably consists of successive layers
 of tinfoil and specially prepared wax paper. The tin foil forms the plates
 of the condenser, and the paper is the
 dielectric of insulating material.
 The variable type of condenser
 consists of two sets of metal plates
 which, in the majority of cases. con stst of aluminium, so arranged that
 one set of plates is stationary and the
 other set moves in and out of the
 stationary set. In this type of con
 denser. air is generally used as the
 dielectric.
 Warning to Radio Fans
 In connection with the variable
 type of condenser. this warning to
 radio fans is very timely: Owing to
 the tremendous expansion of interest
 in the radiophone, broadcasting con-
 densers have become classified by
 the number of plates that they con-
 tain. A large number of "fly by
 night" manufacturers have entered
 this profitable field and are turning
 out condensers on this basis. The . number of plates, however. is no tn- dication of the value or capacity of
 condenser and this fact should be
 borne in mind by the radio fan when
 he is making his purchases, as will be shown later on.
 A condenser has the electrical property known as "eapacity." Like
 all other electrical properties. this is
 measured by certain standard
 which is known by the name tfarad." In other words, "farad" is the basic unit of measurement of capacity in an electric circuit. and the name was given in honor of Michael Faraday-
 one of the electrical pioneers.
 Basic Unit Is Too Large
 Now for all practical purposes, the farad is far too large a measurement
 to be used. and the consequence is that it is divided into millionth parts,
 which are known as "microfarads;" or, using the common abbreviation,
 "mfd;" thus, a condenser Is said to nave a Cd dBAClLy oI uVO
 The determining factors govern ing the amount of capacity in the condenser depend upon the area of the plates themselves in the first l place; and, secondly. the nature and thickness of the dielectric between them For instance, in a valuable condenser. using air as dieiectric, the capacity of the condenser will depend upon the distance which ! separates the different plates from each other. This can be clearly seen when 1t Is pointed out that the closer the plates are together, the thinner is the volume of air between them and consequently the greater will be the capacity of the condenser. Cor respondingly. the further apart the plates are. the lower will be the ca- pacity.
 From this 1t will be seen that since the capacity of the condenser depends upon the area of the plate, as well
 as the thickness and nature of the dielectric. rating a condenser simply by the number of plates it contains is not true indication of it's value in the circuit. The only indication that can be correctly obtained is by the actual size of the plates themselves. Variable condensers are used in the oscillating circuits of radio re- ceiver, or, to put 1t in another way. in the wireless circuits of the appa- ratus. They are made variable in order that the amount of capacity in these circuits can be adjusted, so that the circuit itself can be placed into resonance with the wave length of the incoming signals.
 Condenser Can He Charged Now the condenser has very pe- culiar property. It can be charged up and discharged. When the current Is applied to the circuit in which a condenser Is placed the condenser will store up charge of electricity on its dielectric. up to the limit of it's capacity. In the case of direct cur rent the current will flow up to the time that the condenser is charged after which there will be no further passage of the current.
 With alternating current, however we have a different situation entirely. | The current. first of all, charges the condenser with positive electricity l and immediately reverses this charge with the alienation of the current | itself. Consequently the condenser of 1 fers a free path. for the passage of | alternating currents. The facility with which these currents will pass | through condenser depends entirely upon the frequency. Therefore. the | higher the frequency. the more easily | will the currents pass through the | condenser.
 As we are dealing with frequencies l in excess of 50,o00 cycles a second, l so far as wireless is concerned, 1t ! win be seen that condenser is thus l enabled to perform very important l function in the wireless circuit. as it l offers very easy part to the pas ! sage of these currents.
 This Is particularly important when