. The Bell System technical journal . ent plane directive diagram. The procedure for testing the termination has been simplified throughthe measurement, by a substitution method, of the antenna terminalimpedance as the frequency is varied over the required frequency readjusting the termination, until these measured values areconstant, the required value is obtained. The schematic diagram of the impedance measuring equipmentemployed is shown in Fig. 16. In the actual apparatus, the individual BALANCED HIGH-FREQUENCYOSCILLATOR Hkr C| THERMO-COUPLE A^ C2 C3 C3 TO ANTENNA OR RESISTANCE STA
. The Bell System technical journal . ent plane directive diagram. The procedure for testing the termination has been simplified throughthe measurement, by a substitution method, of the antenna terminalimpedance as the frequency is varied over the required frequency readjusting the termination, until these measured values areconstant, the required value is obtained. The schematic diagram of the impedance measuring equipmentemployed is shown in Fig. 16. In the actual apparatus, the individual BALANCED HIGH-FREQUENCYOSCILLATOR Hkr C| THERMO-COUPLE A^ C2 C3 C3 TO ANTENNA OR RESISTANCE STANDARD Fig. 16—Schematic diagram of impedance measuring equipment. 152 BELL SYSTEM TECHNICAL JOURNAL parts are separately shielded and symmetrically arranged so that theassembly can be attached to a portable balanced oscillator used forother work. Such a combination is shown in the photograph of Fig. referring to Fig. 16, the condensers marked Ci control thedegree of coupling while maintaining an accurate balance to Fig. 17—Impedance measuring equipment and balanced oscillator. Cl is a condenser used for anti-resonating the complete circuit, thisanti-resonance being indicated by a thermocouple deflection. Thecondensers labelled Cz are large blocking condensers which have beenadded to the circuit to permit the measurement of the value of thevariable substitution resistance without the necessity of disconnectingthat resistance. A pencil lead is usually employed as this resistor. HORIZONTAL RHOMBIC ANTENNAS 153 The measurement consists in replacing the antenna by a value ofresistance R which gives the same thermocouple deflection. Thereactive components involved are tuned out in each case by adjustingthe condenser C^. The change in the dial setting of this condenser, asthe resistance is substituted for the antenna, permits the determinationof the reactive component of the antenna impedance. Curve 3, in Fig. 18, shows the terminal resistance versus frequency of
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