MODEL 8559A

YIG-TUNEDOSCILLATOR ASSEMBLY A6, CIRCUIT DESCRIPTION

The YIG-Tuned Oscillator Assembly A6 consists of three parts: a sealed magnet assembly that encloses the YIG sphere and oscillator; a bias board that uses discrete components to establishthe oscillator and amplifier bias, as well as protect the bias supply from noise and voltage overloads; and a mu-metal magnetic-shield can. Field service of the YIG-Tuned Oscillator Assembly A6 is limited to replacement with a new or factory rebuilt unit.

The YIG-Tuned Oscillator A6 is a transistor thin-film microcircuit. It uses a Yttrium-Iron-Garnet (YIG) sphere as the frequency determining structure. The YIG sphere is placed in the gap of an electromagnet to provide a magnetic tuning structure whose field (and thereby the oscillator's frequency) is linearly proportional to the drive current from the Frequency Control Assembly A7.

The Main coil is used for wide range sweeping and tuning with the coil current varying from approximately 69 mA to 138 mA. The FM coil performs these functions for narrow spans (1 MHz/div and less) with its coil current varying from approximately - 18 mA to +18 rnA.

YIG-TUNEDOSCILLATOR ASSEMBLY A6, TROUBLESHOOTING

Power Holes: Power holes that occur at the same point of the sweep in all bands are most commonly caused by the YIG-Tuned Oscillator Assembly A6.

Power holes above 18 GHz are most commonly caused by the type-N RF input connector on the HP 8559A front panel.

Residual FM: The primary cause of residual FM involving the first LO is the Frequency Control Assembly A7.