Radio Broadcast (May-Oct 1922)

RADIO BROADCAST 121 This is a new General Electric crystal receiving set complete with telephone receivers now being featured by the Radio Corporation of America. This little receiver has a wave length range of i8o to 700 meters, made in two steps 180 to 400 and 300 to 700 meters respectively, and tuning is accomplished by a single control to which a pointer is attached which moves over a graduated scale. When the set is not in use, the receivers may be placed inside the metal case by removing the front current. Consequently, an alternating current of very high frequency cannot pass through a circuit possessing a very large inductive value, but it passes through a circuit of small inductive value with great ease. For, possessing a correct value of inductance to pass the high frequency current, each time the magnetic field has built up and the reverse current starts to flow, the high frequency current is itself reversing. The use of the correct inductive values thus aids the flow of an alternating current while too much inductive value greatly impedes or stops the current. The meaning of the word capacity is ability to hold. The capacity of an electrical instrument or circuit is its ability to hold electrons. Free electrons held in suspense by any force are termed an electric charge. A device especially constructed to hold a charge is called a condenser. When a condenser is designed so that its capacity may be continuously varied over a wide scale^ it is called a variable condenser. The diagram shows an inductance and capacity connected in series. If we charge this capacity by means of a battery let us see what happens. There is a positive charge on one set of the condenser plates and a negative charge on the other. These opposite charges are connected by a good conducting circuit through the inductance. Consequently there is a flow of electrons through the inductance until the two charges are equalized. In passing through the inductance, a magnetic field was built up which in turn caused a current to flow in the opposite direction. As a result the charges on the condenser plates are reversed; the plate that was first positive is now negative and vice versa. These charges again neutralize through the inductance. If there were no resistance or losses in the circuit, we would in this way have perpetual charges and reversals of charges. Such a circuit is called an oscillatory circuit, and the current flowing in it an oscillating current. The larger the inductance the longer time it takes the magnetic field to build up, hence the slower the period of vibration of the circuit. The larger the capacity, the greater amount of current required to produce a charge of appreciable strength which will cause a current to flow through the inductance. So the larger the capacity of the circuit, the slower the period of vibration. In radio reception wave lengths between loo meters and 25,000 meters are used. A wave length of 100 meters consists of three million vibrations per second; one of 25,000 consists of 12,000 vibrations per second. When receiving signals from the ether, the aerial and the ground form the two condenser This is a complete crystal receiving set with two wave length controls, one of which acts as a fine adjustment on the other. This receiver is very useful for broadcasting reception. It may also be used to cover wave lengths up to 2,500 meters. It is marketed with a pair of sensitive telephone receivers