HP 8648 A/B/C/D - Changpuak.ch

A4 Reference The reference assembly accepts either an external 10 MHz reference
signal to lock the internal 10 MHz TCXO (temperature-compensated
crystal oscillator) or uses an optional high stability 10 MHz OCXO
(oven-controlled crystal oscillator). The reference assembly outputs
two 200 kHz signals, a 1 GHz signal, and a 10 MHz signal which is
routed to the rear panel.
One of the two 200 kHz signals is routed to the A5 synthesizer and
the other to the A3 modulation section. The 1 GHz signal is routed to
the A6 output assembly.
The 10 MHz REF OUTPUT rear panel signal is a buffered output from
the 10 MHz TCXO or OCXO.
The 200 kHz signals are derived by dividing the 10 MHz signal by 50.
The 1 GHz signal is derived from a 1 GHz VCO that is phase-locked to
the 10 MHz signal.
The reference assembly contains a calibration ROM that contains
factory-generated calibration data that is specific to the assembly.
A5 Sig Gen Synth The synthesizer assembly uses a 200 kHz reference signal from the A4
reference assembly and generates a 500 to 1000 MHz signal using a
divide-by-n phase-locked loop VCO. Frequency and phase modulation
are also done in the synthesizer assembly. The frequency is modulated
both inside and outside of the loop bandwidth. FM outside of the
loop bandwidth is summed with the integrator error voltage and
applied directly to the VCO. FM within the loop bandwidth and phase
modulation signals are applied to a phase modulator along with the
signal from the divide-by-n circuitry and then applied to the phase
detector.
58-6 Theory of Operation
The synthesizer assembly contains a calibration ROM that contains
factory-generated calibration data that is specific to the assembly.