switched on, it supplies 115 volts ac and 28 volts dc to the omega receiver. ANTENNA COUPLER.— The AS-2623/ ARN-99(V) antenna coupler has two loop antennas mounted at 90-degree angles to each other and at 45-degree angles to the aircraft centerline. These antennae are directional, and the proper antenna selection is based upon location to the station being received, relative to the heading to the aircraft. One of the four antenna lobes is selected (A+, B+, A-, or B-) to give the receiver-converter the maximum signal strength from the desired omega ground station. Once the omega has been synchronized, the antenna selection process is automatically controlled by the central computer. RECEIVER-CONVERTER.— The OR-90/ ARN-99(V) receiver-converter consists of five sections. These sections are the receiver section, correlator and digital converter section, computer communication section, discrete storage section, and the power supply section. Receiver Section.— The receiver section consists of the antenna switching matrices, RF amplifiers, IF amplifiers, and a precision frequency generator. The antenna switching matrices sum and phase shift the incoming signals to provide an antenna configuration that will be best oriented to a specific omega station. These circuits also enables test signals to be injected into the omega system. There are three of these matrices in this section, one for each of the operating frequencies. The RF amplifiers remove the IF image and provide attenuation to remove signals far from the operating frequency. There are three of these circuits, one for each frequency, with the only difference between them being the tuning of the bandpass filters and the notch filters. The heterodyne mixers are identical for all three. The local oscillator frequencies produce a 1.33 kHz IF signal. Each frequency used has its own IF amplifier circuit; these circuits are identical for all Figure 2-15.-Omega power control panel. three frequencies.   The limiters in the circuit control the dynamic signal level in the amplifier, preventing saturation of the linear filters. The precision frequency generator generates the precision frequency signals required for operation of the system. The generator consists of a 10.608 MHz crystal oscillator and counters. The counters divide the oscillator frequencies to provide a 13.6 kHz RF test signal, a 1.133 kHz IF reference signal, a 14.733 kHz local oscillator signal, a 176.8 kHz receiver- computer input/output clock signal, a 11.333 kHz RF test and local oscillator signal, and a 10.2 kHz RF test and local oscillator signal. Correlator and Digital Converter Section.— This section converts the phase of the IF signals into digital form. The three channels use identical phase converters. The phase of the IF signal is the navigation information needed by the central computer. Computer Communication Section.— The receiver-converter operation is computer controlled and cannot be operated manually. This section provides a means of communication between the receiver-converter and the central computer. This section receives data requests from the computer and sends the desired data to the computer. Discrete Storage Section.— This section provides a means of storing and controlling antenna switching and test signal gating commands from the central computer for use in the receiver-converter. The discrete storage consist of control line drivers and a decoder circuit. It acts as an interface between the communication section and the receiver sections. Power Supply Section.— The power supply generates regulated and unregulated dc voltages for the system. The power supply also provides for short-circuit protection and for overvoltage protection. The short-circuit protection is for the three regulators, (+16, +5, and -16 Vdc regulators). A short in any of these will cause the regulator to be clamped to ground, and the power supply will need to be reset. The overvoltage protection is for the +5 Vdc circuit. When the output of the +5 Vdc exceeds the breakdown voltage of the Zener, a relay is energized that removes the input power. When this occurs, system power needs to be cycled to reset the protection circuits. 2-17