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285
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CIRCUIT
DESCRIPTION
A
field effect transistor is used in a type of Hartley oscillator
circuit in
me VFO. Part of coil
L1201,
variable capacitor
C1201
(the main tuning capacitor), and fixed temperature
compensating capacitors are used
in-the frequency
determining circuits. The remaining part of coil
LIZ01
is
used for feedback to maintain oscillation.
Diode
Dl201
acts as a switch to add or remove
C1209
and
C1211
from the circuit. These capacitors shift the VFO
frequency so the output carrier frequency remains the same
when you switch sidebands.
Dl201
is switched by the
polar~ty of the voltage applied to its anode by the
LSB
pushbutton switch.
ZDlZOl
is a zener diode to regulate the
i
voltage to the drain of
Q1202.
1
The output of oscillator
01202
is
coupled to
source-follower transistor
Q1203,
which acts as a buffer and
impedance matchingdevice.
01204
and
Q1205
are fix&tuned amplifiers, temperature
compensated by diodes
Dl202
and
D1203.
Variable resistor
R1232
controls the buffer output.
1
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