The R 400 is a single and double sideband radiotelephone receiver for telephony communication in the 1.6-4 MHz coastal telephony band and the 4-27.5 MHz maritime high-frequency telephony bands. The receiver is crystal controlled and has a total of 78 channel facilities distributed as follows: 30 channels in the coastal telephony band and 8 channels in each high-frequency band except the 6 and 25 MHz bands each of which has 4 channels. .The receiver is designed for reception of type A3, A3H and upper-sideband A3A and A3J signals. It is fully transistorized, and widespread use is made of integrated circuits. These features in connection with the fact that no crystal ovens are used cause the receiver to be ready for operation immediately after having been switched on. The receiver incorporates a monitoring loudspeaker, but an external loudspeaker may be connected if desired. Depending on the power pack installed in it, the receiver can be powered from a 12V or 24V battery or from AC voltages normally occurring in practice. Adding new channels to the receiver is very simple. The only adjustment required is adjustment of the crystal frequency. The crystals become accessible after removal of the top cover plate of the receiver. Crystal trimmer capacitors permit making correction for the natural ageing of the crystals which might otherwise within a few years bring the frequencies outside the specification limits.