HP 70427A User Manual page 465

Block Diagram
600 MHz Reference Loop (A7A2)
600 MHz output amplifier's collector supply are also regulated to prevent
noise degradation.
The regulators also improve 40 kHz spurs generated by the module's 40 kHz
switching power supply. Vibrational spurs induced in the crystal resonator
structure are reduced by vibration shock mounting of the 600 MHz
Reference Assembly.
The 600 MHz oscillator output amplifier has four outputs. The main output
is connected to the 600 MHz, 1 watt, power amplifier which drives the
microwave multiplier. The output level is +20 dBm, ±2 dB.
CAUTION The 600 MHz power amplifier output has a DC component of +13.6 V
regulated output voltage, capable of supplying several amps of current. The
DC voltage is to supply bias voltage to the 600 MHz power amplifier.
Appropriate DC blocking must be used to prevent damage to test equipment
when measuring this output.
The 600 MHz outputs to the rear panel are +7 dBm and +21 dBm
respectively, both ±2 dB. The output to the 80 dB isolation amplifier is 10
dBm, ±2 dB.
The 600 MHz oscillator and output amplifier are always active during
normal module operation. The rear-panel 600 MHz outputs are necessary for
performance testing.
80 dB Isolator
The 80 dB isolation amplifier provides the isolation necessary to prevent
multiplier spurs, from the 100 to 600 MHz multiplier, from leaking onto the
600 MHz clean-up loop's main output. The leakage path being eliminated is
from the multiplier output, through the phase detector, through the 600 MHz
phase detector amplifier, through the couplers and into the output amplifier's
output.
The 80 dB isolation amplifier is a tuned three-stage amplifier with
attenuators placed between each stage. The attenuators are necessary to
maintain the amplifier's stability and to provide an additional 23 dB of
isolation. Each stage has a 17 dB gain with about 20 dB of reverse isolation
in the amplifier passband. Outside the 40 MHz passband the reverse
isolation increases at 6 dB/octave. Inside the passband the input and output
return losses are about 10 dB. The output return loss drops to 0 dB outside
the passband. The input level to the 80 dB isolator is 10 dBm, ±2 dB. The
output level is +11 to +16 dBm into the phase detector.
13-30 HP 70427A/HP 70428A User's Guide