Agilent Technologies 8590L Service Manual page 363

Assembly Descriptions and Block Diagrams
RF and LO Section for 8590L, 8591E, and 8591C Spectrum Analyzers
The A7 analog interface assembly controls the center frequency of the
YTO:
• The YTO tune DACs in the A7 YTO driver circuitry determine the
center frequency of the YTO.
• For LO spans greater than 10 MHz, the MAIN SPAN signal is
summed with the output of the YTO tune DAC in the YTO main coil
driver.
• For LO spans less than or equal to 10 MHz, the FM SPAN signal is
summed with the A25 DISCRIM signal in the FM coil driver. The
DISCRIM signal is used to lock the YTO precisely to the center
frequency.
• The control voltages produced using either SPAN signal are then
converted to currents that drive the A6 YTO.
364 Chapter 9