HP 5254C - MIXER ASSEMBLY A3

Section
IV
Model 5254C
selected mixing
frequency.
The filter
has
a
50-ohm
termination
at
both
the input and
output.
The
output
signal
from the filter
(A4) is applied
to
one of the in-
puts of
the
mixer
assembly
(A3).
4-11.
MIXER ASSEMBLY
A3.
(See
Figure 4-3).
4-12. The mixer assembly uses
two
diodes in a
bal-
anced mixer circuit in
order
to
minimize the
genera-
tion of even
order harmonics of
both
the input signal
and the selected mixing frequency.
The combination
of
the terminating
resistor
A3R1 and
the shunting
ef-
fect of
the diodes gives an
input
impedance of 50 ohms
and
provides a low standing
wave ratio
(typically
be-
low
1.
5 up to
3.
0
GHz.
Capacitor
A3C1 provides dc
isolation
up to 100 volts.
A5R1, A5R2, and
A5R3
control the bias
currents
of
the mixer diodes
(A3CR1
and
A3CR2) and are adjusted
for maximum common
mode
rejectionwithinthe video
band
(1
MHz
to 53
MHz).
The non-linearity of
the diodes
(A3CR1
and
A3CR2)
gives rise
to
signals with frequencies
which are the
sum and
difference of
the two mixing
frequencies
Figure
4-2.
Multiplier Amplifier
Assembly Al,
Harmonic Generator
Assembly
A2,
and
Harmonic Selector
Cavity,
Block
Diagram
(5254C)
INPUT
SIG Jl
Y
MIXING
FREQ
FROM HAR
SELECTOR
CAVITY
Figure
4-3.
Low-Pass Filter Assembly
A4,
Mixer Assembly A3, and
Video Amplifier Assembly
A5,
Block Diagram (5254C)
4-2