RCA627 allows to mix a very low frequency top with a stereophonic or a monophonic audio modulation. This top affords to remote control equipments in using the same transmission line as audio.

The classic block diagram of installation comprises the RCA627 coder at the end of the link, for example in the local studio, and at the other end, it means the transmitter, AUF227 decoder. It manages two audio modulations in function of the yes or no presence of the top.

Ex: satellite program on channel A and switching to a regional program on channel B.

The basic frequency is 27Hz but it can be increased in frequency (for example 40Hz) if the link bandwidth is limited at the bottom of the spectrum.

RCA627 includes a bypass system from input A to the output in case of power supply failure installations for radio broadcasting and recording studios.