 The Germans became aware of their losses to night fighters , and began a rush program to introduce a new radar operating on different frequencies . This led to the lower @-@ VHF band FuG 220 Lichtenstein SN @-@ 2 , which began to reach operational units in small numbers between August and October 1943 , with about 50 units in use by November . In February 1944 , No. 80 Sqn noticed a marked decrease in FuG 202 transmissions . By this time the Germans had produced 200 SN @-@ 2 sets , and this had reached 1 @,@ 000 by May . This set deliberately selected a frequency close to that of their ground @-@ based Freya radar sets , in the hopes that these sources would swamp any wide @-@ band receiver set used on RAF aircraft . Early Serrate units were effectively useless by June 1944 , and their replacements were never as successful . 
