HP 608E Operating And Service Manual page 29

'.
Model 6OBE/F
V2
is
removed from the circuit by the position of
switch-wafer 2R, and the sine-wave input circuit is
interrupted by the setting of switch· wafer IF. A de·
tecled RF output signalfrom diode CR2 in the Attenua-
tor Section Is applied to the base of transistor Q2 in
the differential amplifier stage for the development of
a leveling sigr.al as preViously described. R F OUT-
f'UT meter MI also receives the detected signal through
AMPL TRIMMER pushbutton switch S6. Transistor
Q3 in the differential amplifier stage is terminated In
a network conSisting of resistor R263 and capacitor
C206; however, RF OUTPUT control resistor R212 Is
connected In the circuit and controls conduction of the
differential amplifier stage. Pulse Amplifier Q5 Is
disabled by the ground applied to the base circuit
through MODULATION switch-wafer 3F. Leveling
signal output of the differential amplifier stage is
passed through Amplifiers
Q4,
Q6, Q7 and Modula-
tors Q8-Q9 to the input circuit of Power Amplifier
V8. RF OUTPUT meter MI displays a leveled RFout-
put from the instrument as selected
by
the RF OUT-
PUT control and Attenuator Control. AMPL TRIM-
MER pushbutton switch S6 is returned to operation in
conjunction with AMPL TRIMMER capacitor Cl7B for
peaking the RF output uSing the leveling signal feedback
from Modulators QB-Q9.
4-51. ATTENUATOR SECTION.
4-52. To extract power from the RF Generator Sec-
tion, a piston-type attenuator is used. The attenua-
tor housing projects through the rear of the generator
housing, and provides an open-ended termination near
the power amplifier plate-circuit inductor. A single·
turn pick-up loop at the end of the attenuator probe
couples energy to an impedance-matching network
consisting of capacitors C69 and C37, and resistors
R58 and R59. Capacitor C37 is a movable slug in the
probe body that Is used to adjust the standing· wave
ratiotoamlnimum value when RF OUTPUT connector
J4 is terminated In a 50-ohm load.
4-53. The front-panel mounted Attenuator Control
moves the probe in the aUenuator housing, and con-
trols the amount of RF energy passed to the output
connector. In both the Model 608E and 608F. cali-
bration is accomplished by adjusting the RF OUTPUT
and AMPL TRIMMER controls for a steady +7 dBm
(ATTENUATOR CALIBRATED) indication on the RF
OUTPUT meter across the frequency range in use.
An
adjustment of the Attenuator Control after calibra-
tion procedures are completed prOVides the RF out-
put level indicated on the control dial as long as the
RF OUTPUT meter needle remains in the ATTENUA-
TOR CALIBRATED position. In the Model 608E only,
an rf output between +7 dBm and +13 dBm can be se-
lected. The AUenuator Control is set to the +7 dBm
position (maximum clockwise), and the RF OUTPUT
and AMPL TRIMMER controls are adjusted for the
R F OUTPUT meter indication of +7 dBm as previously
discussed. The desired output level above +7 dBm is
then selected by operation of the R F OUTPUT control
only. and the output is read directly from the RF OUT-
PUT meter.
Section IV
4-54. Two parallel wires crossing the open end of
the attenuator housing are used to provide a sample
of RF energy delivered by Power Amplifier V8. The
energy is applied to the Bolometer through ferrite-
bead RFCI, which provides isolation between the
Bolometer and Attenuator. The Bolometer contains
frequency-response coil Ll7, diode CR2 and resistor
R60. The RFsignal detected across resistor R60 and
diode CR2 is passed throughanRFfilter conSiSting of
capacitor C38 and resistor RU9. Thedetected Signal
is then applied through RFI filter FL8 to the Modula-
tion Meter Section discussed in paragraph 4-60, and
to transistor Q2 in the Amplitude ModulaUon Section
discussed in paragraph 4-40.
4-55. CALIBRATOR SECTION.
4-56. The Calibrator Section consists of 5-MHz Oscil-
lator V9A, I-MHz Oscillator V9B, Harmonic Genera-
tor and Mixer CRI, Amplifiers VIOA and VII. and
output transformer T3. The oscillator and mixer
circuits are Illustrated in Figure 7-4, while the ampli-
fiers and transformer are located on Figure 7-5.
4-57. The 5- MHz Oscillator is a crystal-controlled,
electron-coupled oscillator utiliZing the pentode half
of a type 6UB tube. The plate and screen circuits are
tuned to the crystal frequency of 5 MHz by coils L6
and L7. Trimmer capacitor C23 is used for fine-
frequency adjustment of the oscillator. The I MHz
Oscillator consists of the triode portion of the tube.
with coil Ll8 used to adjust the osci'Uator to a point
where the fifth harmonic is synchronized with the 5-
MHz output of Oscillator V9A. WhenXTAL CAL switch
84 is set to the 5-MC position, only Oscillator V9A is
active. In the I-MC position both oscillators are
operating, with Oscillator V9A referencing the i-MHz
oscillator.
4-58. The output signai from Oscillators V9A or V9B
is passed across dc blocking capacitor C24 to diode
CRI which acts as a harmonic generator and mixer.
The anode of diode CHI is inductively coupled to the
output circuit of Power Amplifier V8 by running a lead
near the plate of the amplifier. Oscillator harmonics
within the diode are mixed with RFoutput signals to
produce audio-beat frequencies across resistor R50
in the grid circuit of Amplifier VIOA. The output of
amplifier VIOA is again amplified in VII and applied
across capacitor C36 to 600-ohm, line-matching trans-
former T3. The secondary of transformer T3 is con-
nected to XTAL CAL OUTPUT connector J3 where the
calibrating signals can be monitored. XTAL CAL
GAIN resistor R56 provides front-panel control of the
audio level output at connector J3.
4-59. MODULATION METER SECTION.
4-60. The Modulation Meter Section consists of a
detector network in the Bolometer portion of the At-
tenuator Section, Amplifiers Vl8 and V19. Rectifier
4-7