 Meanwhile , Hibberd had successfully built a new push – pull amplifier using two of the same tubes but working in the 1 @.@ 25 @-@ meter band , an upper @-@ VHF band ( around 220 MHz ) ; below 1 @.@ 25 m the sensitivity dropped off sharply . Gerald Touch , originally from the Clarendon Laboratory , converted the EMI receiver to this wavelength by using the existing set as the intermediate frequency ( IF ) stage of a superheterodyne circuit . The original 45 MHz frequency would remain the IF setting for many following radar systems . On its first test on 17 August , Anson K6260 with Touch and Keith Wood aboard immediately detected shipping in the English Channel at a range of 2 to 3 miles ( 3 @.@ 2 – 4 @.@ 8 km ) . The team later increased the wavelength slightly to 1 @.@ 5 m to improve sensitivity of the receiver , and this 200 MHz setting would be common to many radar systems of this era . 
