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SENSITIVE_FIELD_STRENGTH_METER

2014-11-16 18:44  
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SENSITIVE_FIELD_STRENGTH_METER
The two-pole, five-position switch, coils and 365-pF variable capacitor cover a range from 1.5 to 30 MHz. The amplifier uses Darlington npn transistors whose high beta, 5000, provides high sensitivity with S1 used as the amplifier on/off switch. Switch S2 in the left position allows the output of the 1N34 diode to be fed directly into the 50-μA meter (M) for direct reading. When S2 is in the right position, the amplifier is switched into the circuit. Switch S3 is for local or remote monitoring. At full gain setting, the input signal is adjusted to give a full-scale reading of 50 mA on the meter. Then with the amplifier switched out of the circuit, the meter reading drops down to about 0.5 mA. A 2.5-mH rf choke and capacitors C3, C4, and C5 effectively keep rf out of the amplifier circuit.