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RADIO BROADCAST
AMATEUR LABORATORY OF CHARLES P. MADSEN Testing for faulty insulation. A partially completed receiving set is shown on the table to the right
The lab's electrical equipment is greatly dependent on the shop in which many of the instruments are designed and made. The actual transmitting and receiving apparatus is of first importance, and the photograph of 2BH gives an idea of the general trend in amateur shacks toward commercial lines. Mr. Muller's equipment, which has been partially described, is arranged similarly to a ship station which he operated for some time. The receiving set employs variometer regeneration on short waves, with honeycombs for six hundred meters and above, change from one to the other . being effected by telephone switches in the centre panel. A loud-talker, operated from the second step, is not shown in the illustration. A possible and desirable addition to 2BH would be a spark transmitter, either 500 cycle quenched or 60 cycle rotary synchronous.
A charging system for storage batteries is another early consideration which, in the case of D. C, is easily installed by means of resistances or lampbank. If the station is wired only for A. C, some form of rectification must be employed; the most efficient methods being the two electrode valve (vacuum tube) and the motor-generator.
First among the radio frequency instruments is the wave-meter — in Mr. Muller's station, that prominent piece of apparatus resting on the detector cabinet. A dummy antenna, duplicating the capacity and inductance of the transmitting aerial, is indispensable for preliminary tuning without causing unnecessary QRM (interference). A small transmitting loop in conjunction with a single tube high frequency oscillator finds innumerable experimental adaptations. Nickle and copper plating equipment assures a uniform appearance to all parts without the irksome dependence on the electrical supply house.
A set of meters with auxiliary shunts and resistances is essential for electrical measurements. In delicate experiments the mil-amp and micro-volt meters are used in connection with a potentiometer, while in A. C. transformer work, such as the careful tuning of a spark transmitter, alternating current volt, amp and watt meters are required. For high frequency readings (radiation, etc.) a thermocouple meter is given preference over the hotwire type. The direct reading ohm-meter (an English invention, known, 1 believe, as the Evershad Megger) is an instrument that is slowly finding its useful wa\' into the amateur