The synchro resolver plays a vital part in the navigation role of the aircraft. In the simplest of terms the resolver is a rotary transformer and its shaft angle is presented in the Sine/Cosine format. The resolver is linked mechanically to the azimuth card in the pilots “Omni Bearing Selector” (OBS) or in simpler terms the navigation indicator. The mechanical link between the two essentially converts the magnetic radial or bearing the pilot wants to fly inbound to the navigational ground station. The radial can be from 0 to 360˚ as marked on the azimuth card and this tells the navigation receiver what radial or bearing the pilot has selected and will drive the pointers and flags on the OBS accordingly to satisfy the pilot’s intentions.

The synchro resolvers are sent a portion of the received ground signal from the navigation receiver that the pilot tunes to a specific frequency based on where he wants to fly to. When the pilot rotates the OBS azimuth card to reflect the direction he wants to fly he then modifies this signal to let the receiver know where he wants to go and consequently when to center the indication on that OBS to inform the pilot that he is centered on the course he has selected.

The alignment of the resolver in the OBS is critical to keeping the pilot properly centered on the airway in the sky. With the introduction of the GPS over the last decade this same OBS is used and more importantly the GPS allows the pilot to fly in any direction at anytime and is not limited by the dissipating ground station radiated signal over distance as GPS is satellite based. When aligning the resolver in the instrument lab the avionics technician can use the paired navigation receiver or align the unit in a stand alone condition. The resolver must be loosened from its mounting and pyshically rotated to match the electrical indication with the bearing mark indicated on the azimuth card. The alignment point will vary with the manufacturer of the equipment but the end result is the same as the resolver must track the bearing indication on the azimuth card as it is rotated from 0 through 360˚. While equipment has changed dramatically from the 1940’s the pilot’s requirement to navigate in the air is still to a large degree dependent on this type of equipment in both analog and digital forms.