Heathkit HW-9 User Manual

Page
98
Heathkif
CIRCUIT
DESCRIPTION
Refer
to
the
Schematic
(fold-in) while you read
the
following
information. The
component
numbers are
arranged
in the
following groups to
help you locate
specific parts
on the
schematic, circuit boards,
and
chassis.
i
1-99
Parts
mounted on
the chassis.
101
-
299
Parts mounted
on the
oscillator circuit
board.
301
-
599 Parts mounted
on the T/R
circuit board
and the RF probe.
RECEIVER
SIGNAL FLOW
During receive, the
incoming
signals that are
present
at
the antenna
connector pass
through a
low-pass
filter
on the T/R
(transmit/receive)
circuit
board. The
Band switch
selects the
proper filter,
which rolls off
the high
frequencies
on each band.
A diode
switch
routes this
filtered signal
through a bandpass
filter.
The
resulting signal is
mixed with a
premix signal
to
produce an 8.83
MHz IF
signal.
The 8.83
MHz IF signal
is routed
through another
diode
switch; then it
is amplified
and passed
through a
4-pole IF filter. The
signal is
amplified
again
before it is routed to
the product
detector. An
AGC
(automatic gain
control) voltage is
produced
at this point to
keep the 2nd
IF amplifier
operating
linearly.
The product
detector converts the 8.83
MHz IF sig-
nal to
audio frequencies,
which then pass through
either
a
wide or a
narrow audio-active
filter. An
audio frequency
amplifier
then amplifies this fil-
tered signal so
it can drive an
8-ohm speaker or
a
set
of headphones.
TRANSMITTER SIGNAL
FLOW
Although
the
transmitter
signals flow in a direction
that is opposite to
the receiver, the stages
for both
modes
are very similar.
During
CW
transmissions,
an 8.8307 MHz signal is
coupled to
the 2nd mixer
where it is mixed with
a
premix signal from
the oscillator circuit
board
to
produce the desired
transmitter signal. This signal
is then filtered by
the same bandpass
filters that are
used
during the receive mode
before it is pre-
amplified and applied to
the power
amplifier.
The
power amplifier is made up
of two transistors
in parallel to produce
an RF output
signal. This sig-
nal is
filtered
by
the
proper low-pass filter
for
the
selected
band to reduce
harmonic
radiation before
it is applied to the
antenna.
The
following sections
describe the operation of
each
circuit in greater
detail.

Heathkit HW-9 Specifications

General

Brand	Heathkit
Model	HW-9
Category	Transceiver
Language	English