CFK503 is a UHF full‑duplex stationary intercom unit in a 19-inch, 1U rack frame. It comprises the CST50‑D transmitter and CSR50‑D receiver (both 400–550 MHz, 300 mW) with 16 preset frequencies per link, selectable within a 7 MHz switching range. The RST393 rack frame provides a mains supply. The CSR50‑D includes a compander circuit and CTCSS decoder, suitable for professional intercom applications.