 Two experimental versions of the Mk . II were tested . The AIH unit used GEC <unk> <unk> valves in place of the Acorns for additional power , the H standing for high power of about 5 kW . A test unit fitted to a Blenheim IF proved promising in March and a second was delivered in early April but development was ended for unknown reasons . The AIL had a locking timebase , which improved maximum range , at the cost of a greatly increased minimum range of 3 @,@ 000 to 3 @,@ 500 feet ( 0 @.@ 91 – 1 @.@ 07 km ) and work was abandoned . 
