HP (Hewlett-Packard) HP 85660B ユーザーズマニュアル
The VCO is a varactor tuned oscillator which tunes 75 to 150 MHz. Varactors
CR2,
CR3, and CR4 form a series-tuned resonant circuit with L4 and L5. This series circuit
connects the emitters of
connects the emitters of
and
Q2 is a common-base amplifier whose load impedance is
made up primarily of
R14, and R15. The voltage across the load is coupled to the base of
emitter-follower
which drives the series resonant circuit.
Transistors Q5 and Q6 and associated components form a filtered -32 V source to bias the
varactor tuning diodes. In the absence of tuning current, the varactor bias is set by R2 to
approximately -17 V. Tuning current from the
varactor tuning diodes. In the absence of tuning current, the varactor bias is set by R2 to
approximately -17 V. Tuning current from the
PLL2 Discriminator passes through
the 50
low-pass filter and acts to pull this bias voltage in a positive direction. Tuning
sensitivity is set by R4, to -10
Q4 is a grounded-base amplifier to isolate the VCO from the load circuits. The output of Q4
is filtered, attenuated, and used to drive the
PLL2 Divider.
Q3 isolates the VCO from the dividers and develops the required drive voltage. Note that all
of the dividers and gates are ECL with
hooked to
V and
grounded. U3 divides
the VCO frequency by 5; to the range of 15 to 30 MHz.
provides isolation. U2 divides
the output by 5; to the range of 3 to 6 MHz. U2 then further divides by 2 and
divides
the output by 10, to the range of is 0.15 to 0.30 MHz. The output of
is fed to the
Discriminator.
U5 functions as a single-pole double-throw switch, controlled by SW2. For frequency spans
greater than n
x
5
up to n
x
100
SW2 is TTL high, routing the 3 to 6 MHz signal
from U2 through
and
to the
Up Converter (n is the harmonic
mixing number). When the frequency span is n x 5
or less, or greater than n x 5 MHz,
SW2 is low, routing the 0.15 to 0.30 MHz signal from
through
and
to the
Up Converter. R33 and R34 shift the TTL levels to ECL levels.
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