US Army BC-221-T Frequency Meter

US Army BC-221-T Frequency Meter

This World War Two surplus item was part of the equipment Geoff Perry and Derek Slater used at the Kettering Grammar School to track Soviet space activity. It is of American manufacture and versions were produced in large quantities by a number of different manufacturers - this version was made by Zenith Radio Corporation.

Slater and Perry worked at the Kettering Grammar School together and shared an interest in space. They used borrowed and inexpensive equipment to teach their students how to track satellites. In the process of doing this, the Kettering Satellite Tracking Group was born - which in turn led to the discovery and announcement of a secret Soviet launch site at Plesetsk, securing the Group worldwide media attention.

This Frequency Meter was very stable and was used to provide a reference signal. By setting it to match the satellite frequency a Marconi CR-100/2 communications receiver was tuned to it, and, by definition, was therefore tuned to the satellite. The signal performed a secondary function. The satellite emitted a CW (Continuous Wave) signal which was inaudible through headphones or speaker. By setting the frequency meter slightly away from the satellite, the signal became audible as a tone (or bleep) with an audio frequency equivalent to the difference between the two radio frequencies. This is called a "Beat Note" or "Beat Tone". The two frequencies were usually set to produce a tone of about 1 kHz.

This is not the Kettering Group’s original BC-221. In 1960 a local radio amateur in Kettering, Cyril Dobson, loaned a BC-221 to Geoff and Derek. When the Kettering Group started tracking in earnest (1964), Derek Slater acquired his own frequency meter. At least two different models were used over time including this particular one.