The Signal Corps BC-221 is a WWII-era frequency meter used by the US Army to accurately measure and set radio frequencies. It is a heterodyne frequency meter that covers a range of 125 kHz to 20 MHz. The BC-221 utilizes a 1000 kHz crystal oscillator for calibration and provides accurate frequency measurements with an accuracy of about 100 Hz.
Frequency Measurement:
The BC-221 is designed to measure the frequency of radio signals, both for transmitters and receivers.
Calibration:
It includes a 1000 kHz crystal oscillator that serves as a reference for calibrating the variable frequency oscillator within the meter.
Accuracy:
The device offers a high degree of accuracy, with a reported precision of around 100 Hz.
Notice includes fairly rare headsets and some cables and attachments.