 The RAE 's comments about the self @-@ exciting transmitter were not random : they were referring to work that was just coming to fruition at EMI as a direct result of Lewis ' earlier contract . EMI engineers Alan <unk> and Eric White had developed a system that dispensed with a self @-@ exciting transmitter circuit and instead used a separate modulator that fed the signal into the transmitter for amplification . The oscillator signal was also sent to the receiver , using it to damp its sensitivity . The combined effect was to sharpen the transmitted pulse , while reducing ' ringing ' in the receiver . In a test in May 1940 , Hanbury Brown was able to clearly see the return at a range of 500 feet ( 150 m ) , and could still make it out when they approached to 400 . 
