Heathkit HM-2102 - Page 24

Page 20
Ge JHEATHKIT:
CIRCUIT DESCRIPTION
Refer to the Schematic while reading this “Circuit
Description.”
SWR BRIDGE CIRCUIT
Toroid coil L1 is a current pickup element for forward and
reflected power. A bus wire is routed from the Input jack
through toroid coil L1, and then to the Output jack. A
transmitted signal routed along this wire induces a current in
coil L1. The voltage formed in coil L1 is rectified by diode
D3 and decoupled by capacitor C7 and resistor R4. Reverse
power readings are determined, in the same manner, by the
circuit consisting of diode D2, capacitor C8, and resistor R5.
Forward and reverse voltages are connected to the meter
through switch S2, Sensitivity control R9, and Function
switch S3.
Resistor R2 is a ground-return path for diodes D2 and D3.
Capacitors C3, C4, C5, and C6 form a voltage divider circuit
to balance the capacitive effects of the bifilar (doubled)
windings in coil L1, which provides correct SWR readings.
POWER METER CIRCUIT
Current is induced in toroid coil L1 in the same manner as
for the SWR bridge circuit. Resistor R3 forms a load across
coil L1 to reduce the Q of the coil circuit. This prevents the
transmitted frequency from affecting the wattmeter.
The wattmeter is calibrated by measuring the voltage at
control R6, which varies the current going to the meter.
Resistors R7 and R8 are voltage dividers for the two power
ranges: 25 watts and 250 watts.
Capacitors C1 and C2, diode D1, and voltage divider resistor
R1 through the calibrate jumper complete a voltmeter
circuit for the wattmeter calibration.
Ferrite beads L2 through L6 prevent RF from traveling
through the cable into the readout circuits.
CIRCUIT BOARD X-RAY VIEW
NOTE:
To
identify
a
part
shown
in
this
View,
so
you
can
order
a
replacement,
proceed
in
either
of
the
following
ways:
Refer
to
the
place
where
the
part
is
installed
in
the
Step-by-Step
instructions
and
note
the
“Description”
of
the
part
(for
example:
2200
&,
.005
yF,).
100A,
B.
Look
up
this
Description
in
the
‘’Parts
List.”
(Viewed from foil side)
Note the identification number of the part
(R-number, C-number, etc.).
B. Locate the same _ identification number
(next to the part) on the Schematic. The
“Description” of the part will also appear
near the part.
Cc. Look up this Description in the “Parts
List.”