HP 70427A User Manual page 437

Block Diagram
General Theory of Operation: 600 MHz Reference Chain
General Theory of Operation: 600 MHz
Reference Chain
Overview
The 600 MHz Reference (Assembly A7) produces the low noise, tunable
reference signal for the microwave multiplier. It also produces auxiliary
output signals at 10, 100, and 600 MHz which are accessible from the rear
panel of the module.
The 600 MHz output is produced by first multiplying the 10 MHz,
oven-stabilized timebase to 100 MHz. This signal is the reference frequency
for the 100 MHz noise clean-up phase-locked loop (PLL). The clean-up loop
reduces the noise added to the signal by the 10× multiplication process at
carrier offsets greater than the loop's bandwidth (default=126 Hz).
The 100 MHz clean-up loop produces two auxiliary outputs available at the
rear panel.
The main output of the 100 MHz clean-up loop drives the 10× multiplier to
produce 600 MHz. This signal is the reference frequency for the 600 MHz
noise clean-up loop. This PLL reduces the noise added to the signal by the
6× multiplier at carrier offsets greater than its loop bandwidth
(default=10 kHz). The 600 MHz clean-up loop also produces two auxiliary
outputs available at the rear panel. The main output of the 600 MHz clean-up
loop is the 600 MHz Reference which drives the microwave multiplier.
Tuning sensitivity of the 600 MHz Reference is adjustable in three steps,
0.05 ppm/V, 1 ppm/V and 20 ppm/V, plus the default mode of 0 ppm/V.
Tuning is done by injecting the voltage control signal, from the front panel,
into one of the three different oscillators in the 600 MHz Reference.
The 0 ppm/V or CW mode is produced by grounding the tuning port of the
10 MHz timebase, while both the 10× and the 6× multipliers and their
associated clean-up loops are operating and phase-locked back to the 10
MHZ timebase.
The 0.05 ppm/V mode is the same as the 0 ppm/V mode, except the front
panel voltage control signal is connected to the 10 MHz timebase frequency
control port.
The 1 ppm/V mode is implemented by turning off the 10 MHz output and
10× multiplier and reconfiguring the 100 MHz clean-up loop. The loop's
100 MHz voltage controlled crystal oscillator (VCXO) is now controlled by
the front panel voltage control signal. The 6× multiplier, and the 600 MHz
clean-up loop are now locked only to the 100 MHz VCXO.
The 20 ppm/V mode is produced by turning off the 6× multiplier and
reconfiguring the 600 MHz clean-up loop. The loop's 600 MHz surface
13-2 HP 70427A/HP 70428A User's Guide