OBM

Out of band noise.

Odd Field

The half frame of a television scan which is composed of the odd numbered lines.

Off set-fed Antenna

An antenna whose reflector forms only part of a paraboloid of revolution, usually excluding the pole or apex, such that a front feed causes no aperture blockage.

OFHC

Abbreviation for oxygen-free, high conductivity copper. It has no residual deoxidant, 99.95% minimum copper content and an average annealed conductivity of 101%.

Ohm

A unit of electrical resistance.

OMT

Orthogonal-Mode Transducer or otho-coupler; waveguide component that separates or combines othogonally polarized signals.

Orthogonal

Mutually at right angles (e.g., horizontal and vertical polarization, or right-hand left-hand circular polarization).

Orthomode Coupler

A waveguide, generally a three-port device, that allows simultaneous reception of vertically and horizontally polarized signals. The input port is typically a circular waveguide. The two output ports are rectangular waveguides.

OTS

Orbital Test Satellite. Pre-operational test vehicle for Eurpoean Communcations Satellite.

Oxygen Index

Percentage of oxygen necessary to support combustion in a gas mixture.