Heathkit HW-12 - Page 6

through receive-transmit bandpass coil L2 to re-
ceiver mixer stage V8B. In V8B, the incoming
signal is mixed with the VFO signal from V14
to produce the IF signal, The IF signal from V8B
passes through the crystalfilter, receive-trans-
mit IF amplifier V3, and then to receiver IF
amplifier V9. The crystal filter passes only the
IF signal and rejects all others.
Amplified signal from V9 is fed through IF
transformer T3 to product detector V11A. In
the product detector, the incoming signal is mixed
with a signal from the carrier oscillator topro-
duce an output signal that contains only the re-
ceived voice frequencies,
The voice frequency signal is amplified by AF
amplifier V12B. A portion of this amplified sig-
nal is used to obtain a control voltage which is
re
fed back to some of the preceding stages to main-
tain the volume at a constant level over a wide
range of received signal strength. This is called
AVC (automatic volume control), Finally, the
voice signal is amplified by AF output amplifier
V12A and is then applied to the speaker output
of the Transceiver,
To keep the speaker output from tripping the
transmitter VOX stages, aportion of the receiver
output signal is fed toan anti-trip circuit to keep
the relay from switching to transmit operation,
POWER SUPPLY
Operating voltages for the Transceiver are ob-
tained from a separate power supply. The volt-
age and current values required are listed in the
Specifications section of the manual.
CONSTRUCTION NOTES
This manual is supplied to assist you in every
way to complete your kit with the least possible
chance for error, The arrangement shown is
the result of extensive experimentation and
trial, If followed carefully, the result will be
highly stable and dependable performance, We
suggest that you retain the manual in your
files for future reference, both in the use of
the equipment and for its maintenance,
UNPACK THE KIT CAREFULLY AND CHECK
EACH PART AGAINST THE PARTS LIST. In so
doing, you will become acquainted with the
parts, Refer to the information on the inside
covers of the manual to help you identify
the components, If some shortage or parts
damage is found in checking the Parts List,
please read the Replacements section and sup-
piy the information calied for therein, inciude
all inspection slips in your letter to us,
Resistors generally have a tolerance rating of
10% unless otherwise stated in the Parts List,
Tolerances on capacitors are generally even
greater, Limits of +100% and -20% are common
for electrolytic capacitors,
We suggest that you do the following before work
is started:
1. Lay out all parts so that they are readily
available.
2. Provide yourself with good quality tools.
Basic tool requirements consist of a screw-
driver with a 1/4'' blade; a small screw-
driver with a 1/8" blade; long-nose pliers;
wire cutters, preferably separate diagonal
cutters; wire strippers or a penknife for
stripping insulation from wires; asoldering
iron and rosin core soider. A set of nut
drivers and a nut starter, while not neces-
sary, will aid extensively in construction of
the kit,