basic frequency fo this signal corresponds to a signal subtraction of the pre amplification output signal s 21 from the signal s 23 at the coupler input 23 which is directly proportional to the input signal s i the signal subtraction is achieved through phase opposition of the basic frequency signal shares when the signals are combined e g by using two 90 u00b0 couplers for k 1 and k 2 if the coupler k 2 is a narrow band coupler then the low pass filter tp can be omitted the connections 13 of the first coupler and 24 of the second coupler which are not needed are terminated non reflecting with the impedances r the output signal s 22 of the second coupler k 2 has a signal expanding course le with respect to the input signal s i which is plotted in fig2 b as output power p o above the input power p i such a characteristic course is achieved advantageously by generating a signal with signal compressing characteristic course lk in the pre amplifier vv and by subtracting this signal from a more powerful signal with linear characteristic course ll fig2 a thus in the arrangement shown in fig1 the signal present at input 21 of the second amplifier has less power than the signal at the other input 23 of this coupler meaning the pre amplifying stage is adjusted to a signal amplification of less than one lt o db the same considerations meaning the use of a signal expanding course for compensating a signal compressing power stage also apply.