That Becker set was added to 331 for the air racing - all of the venues requiring VHF but the EFTS Chippy all requiring UHFs for day to day operation. Although the Chippy could be fitted with VHF, it was one or the other and not both. So the Becker set (which was actually designed for gliders) was fitted underneath the front panel where it was barely visible and very hard to tune. Later, when the Swinderby Chippys got a new UHF set which was tunable and didn't rely on crystal presets, the Becker sets were added to the whole fleet to give it a second radio which was required by the RAF regs to fly above cloud. But with no nav kit whatsoever though!