The 344A or B Instrumentation Unit from Collins is the companion of the 51X-2 VHF receiver.

It  translates the received audio signal into signals for navigation instruments like a Course Deviation Indicator (CDI) and Radio magnetic Instrument (RMI).


The 51X-2 VHF receiver has an output contact that  indicates whether tuning is to a  NAV channel (108-117.95 MC) or a comm. channel (118 and up) and another contact to indicate whether this  NAV channel is one of the 20 Localizer (ILS)  channels or a VOR channel.


Like the  51X-2 receiver and 17L7 transmitter,  the instrumentation unit has a 3/8 ATR case .

There is only one  (32-pole) plug for all connections. The unit has a  modular construction., and came in two versions with half, or all modules fitted :

The 344A has 7 modules and can drive one Course Deviation Indicator.

The 344B with 11 modules can drive two Course Deviation Indicators, the Autopilot,  and a Radio Magnetic Indicator (RMI)


The Instrumentation Unit is powered by 115V/400Hz and 27.5Vdc, together 35W in average. The filaments are the main consumer, and a versions exists  were they  are DC powered, and a version with ac powered filaments.


The circuit diagram of the 344A is here

The circuit diagram of the 344B is here  ( with RMI drive capability, shown below )






The Collins 344A or B  VOR/LOC converter was used with the 51X-2 VHF Receiver (bundled as VOR-101) or as part of the  AN/ARC-73 VHF Comm/Nav set.