 With the units in the rear , the only communications method was via the intercom but the <unk> sets used in RAF aircraft used the channel for 15 seconds every minute for the pip @-@ squeak system , blocking communications . Even when modified sets were supplied that addressed this , the radar was found to interfere strongly with the intercom . A speaking tube was tried but found to be useless . Newer VHF radios being developed through this same period did not suffer these problems , and the Blenheims were moved to the front of the queue to receive these units . 
