Abstract: An image control circuit of one terminal apparatus reads image data corresponding to a designated reference numeral from a display content storage circuit and displays this on a monitor device and, at the same time, transmits the data indicating the reference numeral to another terminal apparatus via a communication line. An I/F circuit of the other terminal apparatus receives the reference numeral sent from the first terminal apparatus side nd outputs this to its image control circuit. The image control circuit of the other terminal apparatus stores this data in the display content storage circuit and, at the same time, reads the reference numeral and the image data corresponding to this reference numeral from the display content storage circuit and displays the same in a predetermined part of the screen of the monitor device.

Abstract: A single sideband receiver having a demodulator or mixer for carrier frequency demodulation in response to the output of a controllable variable frequency oscillator and an intermediate frequency demodulator for providing a demodulated signal is provided with an automatic frequency control system comprising a low pass filter for separating a low frequency portion from the demodulated signal a discriminator for detecting the level of the low frequency portion with respect to a predetermined level, and a circuit for controlling the frequency of the variable frequency oscillator in response to the detected relationship between the low frequency portion and the predetermined level.