334 Chapter6
General Troubleshooting
Block Diagram Description
crystal oscillator) or an Option 103 TCXO (temperature-compensated
crystal oscillator). The PLL can also be locked to an external frequency
reference.
The 10 MHz reference also supplies the reference for the frequency
counter on the A2 controller assembly, and the cal oscillator on the A4
log amplifier assembly.
YTO PLL (A7, A11, part of A14, part of A15)
The YTO PLL produces the first LO of the instrument (3.0 to 6.81 GHz).
The YTO output is mixed with a harmonic of the sampling oscillator in
the sampler (A15U100), and the resulting frequency is phase-locked to
the output of the fractional N PLL.
The A15U100 sampler mixes the LO signal from the A7 LODA with a
harmonic of the sampling oscillator. The mixing product, the sampler
IF, is between 60 and 96 MHz (same frequency range as the fractional
N PLL).
Offset Lock Loop (part of A15)
The 285 MHz to 297.2 MHz sampling oscillator is used to sample the
YTO. By changing the offset lock loop programmable dividers, the YTO
frequency can be changed.
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