Abstract: An automatic leveling circuit for a composite video signal is disclosed for use in a modem in a microwave communications system for adjusting the level of the signal at the transmitter while maintaining studio quality. The circuit employs an operational amplifier as the variable gain element and employs a light emitting diode photo-conductor pair in association with the amplifier to control the amplifier gain. In particular, the horizontal synchronizing pulse from the composite video signal is separated and used with a keyed clamp to establish the video at a desired dc reference value and is applied to a sample and hold circuit where the sampled pulse amplitude is held for comparison to an operator adjusted value. The output of the comparator is then used to control the light produced by the light emitting diode in a degenerative sense to hold the video level at the operator adjusted value.