Theory of Operation
2715 Spectrum Analyzer Service Manual 3-7
1st LO Buffer
The 1st LO Buffer consists of a Leveled Amplifier and a Phase GateDetector.
The Leveled Amplifier provides the LO input drive for the 1st Mixer.The Phase
Gate Detector logs 1st LO drift. Thatinformation is then used for frequency
corrections.
Sweep
The Sweep board contains a mi croprocessor interface, horizontal sweep
generator, trigger circuitry, vertical sweep (raster s can) circuitry, video proces-
sing, video line triggering, and graticuleillumination.
This board receives messages from the microp rocessor regarding its operation,
but cannot send messages directlyto the microprocessor.
Various combinations of resistors and capacitors yield t he sweep speed selec-
tions.
The available triggermodes are Free Run, Internal, Line, External, TV Field, and
TV Line. When the video monitor mode is selected,the readout, display storage,
and video filter areturned off. In addition, the resolution bandwidth is set to
5 MHz, the Verticaldisplay mode defaults to Lin, the span setting defaults to
Zero Span, and the sweep ratedefaults to 5 s. The video monitor mode is
turned off from the triggermenu or by selecting another trigger mode.
TV Line Trigger mode causesthe S pectrumAnalyzer to trigger on the selected
video line. The selected li ne, and part of the next line, are display ed.