Abstract: A system and method for simultaneous transmission and receival where the received signal is downconverted in a downconverting unit by using a portion of the transmitted modulated signal as LO for the downconversion. The downconversion is performed to an intermediate frequency signal having a frequency equal to the difference between the frequency of the transmitted signal and the frequency of the received signal. There is provided a common antenna for transmitting and receiving, and a duplex filter in front of the antenna to separate the transmitted signal and the received signal with the transmitter data on the transmitter side having been applied to a modulator. In front of the duplex filter on the transmitter side is provided a power amplifier. On the receiver side there is, in addition, provided a demodulator to permit withdrawal of user data for the user on the receiver side.