HP 8340A Service Manual page 81

Rl, R2, R3,
TP3 should be at approximately -14.B Vdc for correct bias.
100 MHz Buffer Amplifier
Transistors Q9 and QB function as buff er amplifiers to isolate the
vcxo from variations in load which would otherwise cause frequency
pulling of the
which presents a high impedance to the VCXO output. QB buffers the
output of Q9. Components
match the impedance of the collector output of QB to 50 ohms. This
signal, 100 MHz OUT,
The signal at the emitter of QB,
(emitter�follower configuration),
a common-base buffer amplifier. The output at the collector of
Qll, through the tuned circuit of L7,
the power splitter,
In one path,
is a common-emitter amplifier with emitter degeneration
gain stability. The outp�t at the collector of Q6,
tuned circuit of LB,
splitter, T2,
path, the signal goes through a 3 dB pad and a tuned LC circuit
and becomes the 100 MHz O UT signal sent to the A29 Reference Phase
Detector and the A39 P LL3 Upconverter.
In the second path from power splitter T3,
a common-emitter buffer amplifier. The output at the collector of
Q7, through the tuned circuit of L9,
the Quadrupler,
Quadrupler C
The 100 MHz signal from Q7 in Block B is applied to power splitter
Tl. The two outputs of Tl are input to transistors Q3 and Q4,
which form a Class C amplifier,
Positive half-cycles of the 100 MHz signal into Tl turn on Q3
while negative half-cycles turn on Q4. The collector outputs are
connected together to provide a fullwave rectified signal that is
rich in even harmonics. The tank circuit of C3 and LlO is tuned to
pass the 4th harmonic,
MHz Amplifier,
400 MHz Amplifier
Q2 and Ql are both common-emitter amplifiers which have .
approximately 20 dB gain each.
8-108
Model B340A - Service
Rll, R54, and Ll determine the bias and gain of Q5.
B
oscillator. Q9 is an emitter-follower amplifier
L6,
is sent to the AB 3.7 GHz Oscillator.
T3, which splits the signal into two paths.
the signal from·T3 goes to U6 through a 3 dB pad. Q6
C27, and C2B,
which splits the signal into two paths. In each
Block c.
400 MHz. This signal is applied to the 400
Block D.
o·
Scans by HB9HCA and HB9FSX
Cl5, and Cl6 form a tuned circuit to
equal to the input signal
is input to the emitter of Qll,
Cl9, and C20,
is applied to the power
the signal goes to Q7,
C32, and C33,
full-wave rectifier circuit.
Both have tuned outputs to filter
is applied to
(R27) for
through the
is applied to