 Touch , now at RAE Farnborough and having delivered improved versions of ASV , quickly adapted the new oscillator to the existing Mk . III transmitter . Adapting the vertical transmitting " arrowhead " , folded twin @-@ dipole antenna design on the nose of the aircraft , from Hanbury Brown 's work with the Mk . III eliminated any remaining problems . In its first operational tests in July 1940 , the new AI Mk . IV demonstrated the ability to detect another Blenheim at a range of 20 @,@ 000 feet ( 6 @.@ 1 km ) and continued to track it down to a minimum of 500 . Hanbury Brown stated that " it did everything that we had originally hoped that airborne radar would do for night @-@ fighting " . He went on to note that even though Mk . IV arrived only one year after the first Mk . I 's , it felt like they had been working for ten years . 
