CV89 interdigital magnetron (related to CV79 which is a frequency variant). This generates about 300mW at 6.3cm (4.76GHz).

The CV79 and CV89 were used in Wireless Set No.10, which played an important part in the WWII D-Day landings. This was a trailer mounted installation, using pulse modulation to enable 8-channels (e.g. 8 phone lines) over a 50 mile (optical) path. The associated receiver made use of the CV90. The Mk. II version used two CV228 Heil tubes in the transmitter instead of the CV79 or CV89.