The back of the 147.075 Mhz repeater showing the audio, R.F., & cos lines. The repeater cavities are below the RF and controller units. The oscilloscope on the top of the repeater is being used to check on the audio and cos signal levels. Curiously enough just to the left of the repeater is part of an very rare 1860 Oscilloscope showing its self. This older unit uses acoustic cavities or resonators (as they use to call them), gas flame flickering detectors, and a whirling four-sided mirror to measure the frequency and level of audio signals. It's the mirror that is showing.