By using the preamplifier with a short length of shielded cable and clip leads, signals that generally could not generate a readout, generate precise and stable readouts on the counter. The DPDT switch is used to bypass the circuit when amplification is not needed. The preamplifier can also be used for other purposes. For example, the unit was also tested as a receiver preamplifier and increased received signal strength about 6 S-units at 30 MHz.
Frequency-counter-preamp - schematic

A line tap can be used to measure the frequency directly at the output of a transmitter. The entire circuit for that consists of two diodes, one resistor, and one capacitor. The line tap simply picks a low-amplitude signal for measurement by the frequency counter. The tap can be connected to transmitters with an output power of between 1 and 250 W.

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