Anti jamming system comprising a tunable negative jamming signal feedback loop for feedback suppression of a received jamming signal, including an receiver receiving an jamming signal followed by a replica jamming signal generator for generating an replica jamming signal. The receiver comprising a zero IF PLL receiver having a synchronous demodulator and a phase detector, signal inputs thereof being coupled to said input means and carrier inputs coupled to in-phase and phase quadrature oscillator outputs, respectively, of a local voltage controlled oscillator (VCO), said VCO receiving a tuning control signal for tuning the zero IF PLL receiver at the carrier frequency of the jamming signal. The VCO is included in a phase locked loop (PLL) comprising subsequent to the VCO, said phase detector and a loop filter. The replica jamming signal generator includes a modulator with a baseband signal input coupled to an output of said synchronous demodulator and a carrier input coupled to the in-phase oscillator output of the VCO, an output of said modulator being negatively fedback to the input of the receiver.