1. AN AMPLIFIER ARRANGEMENT FOR LOW NOISE LEVEL AMPLIFICATION OF SHORT AND ULTRA SHORT ELECTROMAGNETIC WAVES, COMPRISING A REACTANCE MODULATOR AND MEANS FOR CONDUCTING WAVES THERETO WHICH ARE TO BE AMPLIFIED, AN OSSILLATOR, THE FREQUENCY OF WHICH IS HIGHER THAN THE WAVES TO BE AMPLIFIED, OPERATIVELY CONNECTED TO SAID REACTANCE MODULATOR WITH THE OUTPUT FROM THE LATTER INCLUDING SIDE BANDS ABOVE AND BELOW THE OSCILLATOR FREQUENCY, A FREQUENCY CONVERTER, A SIDE BAND FILTER OPERATIVELY CONNECTING THE OUTPUT OF SAID REACTANCE MODULATOR TO SAID FRE-