Hal Communications AK-1 User manual
.,.
....
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******************"k**"'k****************'"**i'\"-k*
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k·l\;'\"1co.Jc-k*'"*"k*·k··kk·k-k***-1<*
WARRANTY
HAL
Communications
Corp.
warrants
that
the
HAL
Communications
Corp.
factory-wired
AK-1
AFSK
Oscillator
shall
be
free
of
defects
in
materials
and
workmanship
under
normal
use
and
service
for
a
period
of
one
year.
Should
such
defects
occur
within
the
warranty
period,
notify
HAL
Communications
Corp.
promptly.
The
warranty
period
is
measured
from
the
date
of
the
original
invoice
to
the
postmar~-date
of
your
notification
letter.
Do
not
return
your
unit
to
the
factory
for
repair
or
adjustment
until
you
have
received
written
return
authorization.
In
the
case
of
AK-1
AFSK
Oscillator
Kits,
this
warranty
applies
only
to
the
parts
supplied
in
the
kit
and
does
not
apply
to
any
wiring
or
components
which,
in
the
judgement
of
HAL
Communications
Corp.,
were
damaged
by
incorrect
use
or
construction
on
the
part
of
the
kit
builder.
This
warranty
is
and
shall
be
in
lieu
of
all
other
warranties,
whether
expressed
or
implied,
and
of
all
other
obligations
or
liabilities
on
the
part
of
HAL
Communications
Corp.
resulting
from
the
installation
or
use
of
this
oscillator.
The
foregoing
warranty
is
completely
void
on
all
AK-l's
which
have
been
repaired
by
individuals
other
than
HAL
Communications
Corp.
personnel,
those
which
have
been
damaged,
abused,
modified,
improperly
installed,
or
tampered
with,
and
those
which
have
been
subjected
to
improper
voltages
or
currents.
*****************************************"'<***·k·k*·k-;'\-1<***"k***"k**'-k*-1<*
Copyright©
1974
by
HAL
Communications
Corp.,
Urbana,
Illinois.
Printed
in
the
U.S.A.
All
rights
reserved.
Contents
of
this
publication
may
not
be
reproduced
in
any
form
without
the
written
permission
of
the
copyright
owner.
...
~
I"'
""
CONTENTS
1.
INTRODUCTION
..
2.
SPECIFICATIONS
.
3.
OPERATION
OF
THE
AK-1
4.
AK-1
KIT
CONSTRUCTION
5.
INTERCONNECTION
OF
THE
AK-1
WITH
OTHER
EQUIPMENT
6.
TEST
AND
ALIGNMENT
....
7.
DIAGRAMS
AND
PHOTOGRAPHS
8.
PARTS
LIST . . . . . . .
ILLUSTRATIONS
Figure
1.
AK-1
Schematic
Diagram . . . . .
Figure
2.
AK-1
Circuit
Board
Layout
....
Figure
3.
Photograph
of
AK-1
Circuit
Board
Figure
4.
Typical
Connections
to
AK-1
...
Figure
5.
Direct
TTY
Keyboard
Connection
to
AK-1
Figure
6.
AK-1
Connection
to
Tube-type
Demodulators
Figure
7.
Direct
Loop
Connection
of
AK-1
Figure
8.
Connection
to
ST-5
Demodulator
Figure
9.
Connection
to
ST-6
Demodulator
Figure
10.
Wiring
Diagram
for
ST-6
Cabinet
.
Figure
11.
Use
of
AFSK
with
a
Typical
SSB
Transmitter
Figure
12.
Spectra
of
Signals
Generated
by
SSB
Transmitter
1
2
3
5
7
13
15
26
16
17
18
19
20
20
20
21
22
23
24
25
'
.~
:.
("'\.
"""'
1.
INTRODUCTION
The model
AK-1
AFSK
Oscillator
is
designed
to
generate
tone-encoded
teleprinter
signals
for
transmission
by
either
HF
or
VHF
radio.
Encoding
is
accomplished
by
shifting
the
frequency
of
the
internal
oscillator
from
its
normal
rest
frequency
("mark"
condition)
to
a
higher
frequency
("space"
condition)
as
teleprinter
keying
pulses
dictate.
The
rest
or
"mark"
frequency
output
of
the
AK-1
is
the
standard
2125
Hz
audio
tone
and
the
space
frequency
can
be
selected
to
be
either
2295
Hz
(170
Hz
shift)
or
2975
Hz
(850
Hz
shift).
Additionally,
the
"mark"
frequency
can
be
shifted
upward
by
approximately
100
Hz
with
a
telegraph
key
to
allow
for
CW
identification
of
the
radioteleprinter
transmission.
The
input
keying
requirements
of
the
AK-1
are
compatible
with
output
signals
from
the
HAL
Communications
ST-6
and
ST-5
demodulators
and
can
be
easily
keyed
from
other
sources
of
low-voltage
serial
teleprinter
data
.•
Both
hig~and
low-level
audio
outputs
are
available
from
the
AK-1,
providing
a
great
deal
of
flexibility
in
interfacing
the
oscillator
to
various
radio
transmitter
inputs.
A
five-pole
Butterworth
filter
in
the
output
stages
of
the
AK-1
prevents
generation
of
any
spurious
signals
in
the
form
of
harmonics
of
the
original
audio
tones.
The
entire
oscillator
assembly
is
contained
on
one
2
7/8"
X 5
3/4"
circuit
board,
plugs
into
a 12
pin
edge
connector,
and
requires
only
a
keying
voltage
and
+12
volt
power
supply.
The
AK-1
circuit
board
is
compatible
with
other
circuit
boards
in
the
HAL
ST-6
Demodulator
and
the
AK-1
is
a
common
option
included
in
the
factory-wired
ST-6.
The
HAL
AK-1
AFSK
oscillator
circuit
is
based
upon
a
design
described
by
Irvin
Hoff,
W6FFC,
in
the
February,
1969
issue
of
QST
magazine
(page
11)
.
•
1
.
2.
SPECIFICATIONS
Output
Frequencies:
Mark (170
and
850
Hz
shifts)
Space
(170
Hz
shift)
Space
(850
Hz
shift)
CW
ID
(key
down)
Output
Amplitude:
High-Level
Output
Low-Level
Output
.
2125
Hz
2295
Hz
2975
Hz
2225
Hz
100
mV
rms
20
mV
rms
Frequency
Stability
(after
15
minute
wa~-up)
+ 5
Hz
(all
tones)
Standard
Frequency
Shifts
available
170
and
850
Hz
Input
Keying
Voltage
Requirements:
Mark .
Space
less
than
0
volts,
greater
than
-20
volts
greater
than
+5
volts,
less
than
+20
volts
Power
Requirements
Size
2
. . +12 V de @ 30ma
. 2
7/8"
X 5
3/4"
circuit
board
(7.0
X
14.6
em)
•
J-
0-
~""
""
'•
~
""'
3.
OPERATION
OF
THE
AK-1
The
circuit
of
the
AK-1
AFSK
Oscillator
(see
Figure
1,
page
16)
is
made up
of
five
basic
sections:
oscillator,
keyer,
divider,
filter,
and
output
amplifier.
The
signal
is
generated
in
a
unijunction
relaxation
oscillator
(Q4)
at
twice
the
desired
output
frequency.
The
exact
mark
frequency
of
oscillation
is
determined
by
the
combination
of
C2
and
Rll,
Rl2,
and
Rl3
(also
Rc,
if
used).
The
frequency
of
oscillation
is
changed
from
mark
to
space
condition
by
paralleling
the
Rll,
Rl2,
Rl3
chain
with
either
R6
and
R7
(170
shift)
or
R4
and
R6
(850
shift)
series
resistor
chains.
Therefore,
shifting
from mark
to
space
frequencies
is
accomplished
by
changing
the
charging
time-constant
of
capacitor
C2, a
procedure
that
generates
no
abrupt
phase
discontinuities
in
the
oscillator
waveform.
This
is
a
particularly
important
feature
of
the
AK-1
when
it
is
to
be
used
in
a
SSB-type
of
transmitter
system.
For
ipstance,
oscillator
circuits
that
use
tuned-circuits
will
generate
spurious
signals
due
to
phase
discontinuities
when
shifting
from
mark
to
space.
These
spurious
signals
rarely
cause
problems
in
VHF-type
AM
orFM
applications
but
will
cause
radiation
of
illegal
signals
when
used
with
a
SSB-type
of
transmitter.
The
AK-1
will
not
produce
this
type
of
spurious
signal.
Changing
the
frequency
from
mark
to
space
is
accomplished
electronically
by
keyer
stages
Ql and Q2. Keying
voltages
are
presented
to
pin
6
of
the
edge
connector
with
the
convention
that
for
mark
condition
the
voltage
should
be
zero
or
less
(preferably
between
-5
and
-15
volts)
and
greater
than
+5
for
space
condition.
Therefore,
during
mark,
Ql
is
"off"
as
is
Q2
and
the
effective
charging
resistor
for
C2
is
only
the
Rll,
Rl2,
and
Rl3
series
chain.
During
space,·both
Ql
and
Q2
are
turned
"on",
paralleling
either
R4
and
R5
or
R6
and
R7
(depending
upon
which
is
selected
by
Sl)
with
the
Rll,
etc.
chain.
A
separate
keyer
transistor,
Q3,
is
provided
for
CW
identification.
When
pin
7
of
the
edge
connector
is
grounded,
Q3
is
biased
"on"
and
R8
is
placed
in
parallel
with
the
Rll,
etc.
chain,
increasing
the
frequency
by
approximately
100Hz.
Note
that
this
stage
can
be
activated
at
any
time
and
it
is
therefore
important
that
the
key
(or
its
shorting-bar)
not
be
closed
during
RTTY
transmission.
R8
has
been
chosen
to
give
approximately
100
Hz
shift
from
the
mark
tone,
but
the
exact
amount
of
CW
ID
shift
can
be
adjusted
by
changing
the
value
of
this
resistor.
It
is
important
to
note
that
both
space
tone
and
CW
ID
frequencies
are
determined
by
their
respective
resistor
chains
in
parallel
with
the
mark
resistor-chain.
Therefore,
it
is
necessary
that
the
mark
frequency
be
adjusted
first
since
any
change
in
this
resistor
chain
will
affect
all
other
tones.
To
allow
compensation
for
the
wide
range
of
possible
variation
of
the
unijunction
oscillator
transistor,
Q4,
and
timing
capacitor
C2,
both
a
fine
and
coarse
adjustment
are
provided
for
the
mark
frequency.
The
ranges
of
all
potentiometers
have
been
chosen
so
that
it
should
always
be
possible
to
adju.st
to
the
correct
frequencies
without
changing
fixed
resistors
if
the
unit
is
constructed
correctly.
3
The
output
of
the
oscillator
across
resistor
R22
is
a 2
volt
spike
at
twice
the
desired
output
frequency.
The
divider
stage
(BSMV),
Q5-Q6,
is
triggered
by
these
pulses.
The
output
of
the
divider
(measured
at
the
collector
of
Q6)
should
be
a
square-wave
of
approximately
10
volts
peak-to-
peak
amplitude
and
with
a
frequency
equal
to
the
desired
output
frequency
(2125Hz
for
mark
with
key-up).
The
low-pass
filter
removes
all
but
the
fundamental
component
of
the
square-wave,
resulting
in
a
sinusoidal
output
waveform.
R24
is
the
input
terminating
resistor
for
the
filter
and
R23
is
a
divider
to
reduce
the
voltage
output
and
provide
some
isolation
between
the
divider
and
filter.
If
desired,
the
output
of
the
AK-1
can
be
increased
somewhat by
reducing
the
value
of
R23,
but
care
should
be
taken
to
maintain
the
same
parallel
equivalent
of
R23
and
R24
to
keep
the
proper
filter
termination
impedance.
Since
it
is
only
necessary
that
the
filter
provide
rejection
of
the
harmonics
of
the
divider
output
(odd-order
harmonics
for
the
square-wave),
the
filter
does
not
require
critical
timing
and
can
be
assembled
directly.
If
problems
are
suspected
with
the
filter
circuit,
the
pass-band
can
be
checked
by
removing
the
end
of
resistor
R23
from
the
collector
of
Q6
and
substituting
an
audio
oscillator,
observing
the
output
across
C7. The
filter
should
be
"flat"
(within
1.
0 dB) up
to
3000
Hz
and
should
be
of
the
order
of
13
dB
down
at
4250Hz
(2 X 2125)
and
31
dB
down
at
6375
Hz
(3
X
2125).
This
check
is
not
normally
required
and
should
only
be
necessary
if
problems
occur.
Two
outputs
are
provided
from
the
AK-1:
an
attenuated,
high-impedance
output
of
20
mV
rms
for
typical
connection
to
the
high-impedance
microphone
input
on
a
transmitter,
and
a
500
ohm, 100
mV
rms
output
that
can
be
used
for
carbon-microphone
inputs,
to
drive
counters,
and
other
high-level
applications.
Transistor
Q7
is
used
as
an
emitter-follower
isolation
amplifier
to
drive
the
100
mV
output.
When
connecting
to
the
100
mV
output,
it
should
be
remembered
that
the
coupling
capacitor,
C9,
is
electrolytic
and
leakage
inherent
in
any
electrolytic
will
produce
a de
voltage
if
a
very
high
impedance
device
is
connected
to
this
output.
This
is
particularly
true
of
some
counter
input
circuits
and,
on
counters
without
a
blocking
input
capacitor,
can
cause
false
counting.
The
cure
is
to
terminate
the
output
in
lK
to
lOK
ohms.
Another
precaution
for
use
of
the
100
mV
output
is
to
maintain
fairly
low
shunt
capacitance
across
the
output.
Under some
conditions,
transistor
Q7
will
oscillate
in
the
5
to
10
MHz
range
if
the
100
mV
output
is
capacitively
loaded.
The
cure
is
to
reduce
the
capacitance
of
the
load,
or
use
ferrite
beads
on
the
leads
of
Q7. Use
of
resistor
Rx
to
provide
space-tone
pre-emphasis
is
discussed
in
detail
in
the
applications
section
of
this
manual.
Power
required
by
the
AK-1
is
connected
to
pins
5 (+12V @ 30
ma)
and
1
and
12
(ground
return).
An
additional
zener
regulator,
D3,
provides
+8.2
volts
regulated
to
the
oscillator
circuit,
but
regulation
of
the
+12
volt
input
is
also
highly
recommended.
4
~
~
,....,(
\,
4.
AK-1
KIT
CONSTRUCTION
Construction
of
the
AK-1
involves
two
steps:
assembly
of
the
circuit
board
and
interconnection
of
the
circuit
board
to
a power
supply,
control
switches,
connectors,
and
the
rest
of
the
RTTY
system.
Since
there
are
many ways
in
which
the
AK-1
may
be
interfaced
with
other
equipment,
a
number
of
common
interconnection
schemes
are
presented
and
discussed.
The
constructor
should
familiarize
himself
with
all
techniques
discussed
and
then
choose
the
one
that
is
most
convenient
for
his
particular
system.
Obviously,
the
circuit
board
must
be
assembled
in
any
case
and
this
task
may
be
tackled
first.
4.1
Circuit
Board
Construction
Construction
of
the
AK-1
involves
~ssembly
of
most
of
the
parts
on
the
circuit
board
and
then
installation
of
the
board
and
its
edge
connector,
switch,
and
connectors
in
whatever
housing
the
constructor
chooses.
Assembly
of
the
circuit
board
is
quite
simple
and
will
generally
not
require
more
than
one
hour
of
construction
time.
The
circuit
board
layout
in
Figure
2
and
the
photograph
in
Figure
3
(pages
17and
18)
should
be
closely
followed
for
correct
parts
placement.
The
following
assembly
order
is
recommended
for
the
circuit
board.
First,
mount
all
of
the
resistors
on
the
circuit
board,
starting
with
the
four
trimming
potentiometers.
Note
that
each
has
different
resistance
-
locate
the
proper
location
for
each
before
soldering
it
in
place.
The
~
watt
fixed
resistors
can
now
be
mounted
in
the
locations
indicated.
ALL
resistors
are
mounted
in
a
vertical
position
with
the
body
of
the
resistor
placed
over
the
hole
marked
with
a "V"
on
the
circuit
board
layout.
Resistor
locations
marked
"Ra",
"Rb",
and
"Rc"
are
provided
for
series
trimming
resistors
if
required.
They
are
generally
not
required
and
jumpers
should
be
inserted
in
these
locations
initially.
If
trimming
resistors
are
found
to
be
required
upon
alignment,
the
appropriate
jumper
can
then
be
replaced
by
a
series
resistor.
Resistor
"Rx"
location
is
provided
to
allow
a
limited
amount
of
"pre-emphasis"
on
the
space
tone.
Choice
of
this
value
depends
~pon
the
equipment
that
the
AK-1
is
used
with
and
this
location
should
be
left
open
until
tests
indicate
what
value
is
optimum.
Choice
of
~
values
is
discussed·
in
the
alignment
and
test
section
of
this
manual.
The
transistors
and
diodes
should
now
be
mounted,
being
very
careful
to
observe
correct
transistor
orientation
and
diode
polarity.
Note
that,
as
with
the
resistors,
ALL
diodes
are
mounted
in
a
vertical
position
with
the
body
of
the
diode
over
the
hole
indicated.
Place
the
capacitors
on
the
circuit
board
next,
starting
with
the
ceramic
and
mylar
capacitors
first.
When
mounting
the
electrolytics,
observe
the
polarity
marked
on
the
layout.
All
electrolytic
capacitors
are
mounted
in
a
vertical
position
with
the
body
placement
indicated
as
before.
The
.01
~f
polystyrene
capacitor
should
be
mounted
horizontally
in
the
position
indicated.
5
"\
The two 88
mhy
toroidal
inductors
should
be
mounted
last.
The two
halves
of
each
toroid
are
connected
in
"series-aiding"
with
the
"loose-end"
of
one
half
connected
to
the
"sleeved-end"
of
the
other
half
to
form
the
center-tap.
Fasten
the
toroids
to
the
board
with
the
6-32
hardware
furnished
with
the
kit.
The
correct
order
of
assembly
is:
screw-head,
flatwasher,
nylon
washer,
toroid,
circuit
board,
lockwasher,
and
6-32
nut.
The
completed
assembly
should
have
the
screwhead
and
toroid
on
the
component
side
of
the
circuit
board.
This
completes
the
assembly
of
the
circuit
board
and
it
should
be
set
aside
until
the
switch,
connectors
and
power
supply
have
been
mounted.
4.2
Installation
of
the
Circuit
Board
Since
the
AK-1
is
designed
to
be
used
in
conjunction
with
other
RTTY.
equipment,
it
does
not
have
a
self-contained
power
supply
and
must
therefore
be
furnished
with
+12
volts
de
at
30 rna.
This
voltage
can
be
obtained
from
the
demodulator
(such
as
the
ST-5
or
ST-6)
or
other
low-voltage
source.
Whatever
the
source,
the
+12
volts
furnished
to
the
AK-1
should
be
well-
filtered
(free
of
hum
and
noise)
and
reasonably
well
regulated
(zener
regulation
is
quite
adequate).
The
circuit
board
of
the
AK-1
should
be
mounted
in
a
metallic
container
(for
shielding),
away
from
obvious
heat
and
hum
sources.
When
the
AK-1
is
used
with
the
ST-6,
a
circuit
board
location
has
been
reserved
in
the
de-
modulator
cabinet
for
the
AFSK
oscillator.
A 12
pin
edge-connector
is
supplied
with
the
AK-1
kit
to
make
connection
with
the
circuit
board,
but
this
can
be
deleted,
if
desired,
and
connections
made
directly
to
the
circuit
board
at
the
extra
pads
provided.
This
technique
will
allow
the
fingers
of
the
board
to
be
cut-off,
saving
approximately
3/4
inch
in
overall
length
(fingers
plus
edge
connector).
Also
supplied
with
the
kit
are
two phono
pin-jacks
for
audio
output
connections
and
two
~"
phone
jacks
for
hand-key
and
RTTY
keying
signal
input.
A
DPDT
toggle
switch
is
provided
to
change
the
shift
of
the
AK-1.
Since
the
AK-1
requires
only
one
pole
of
the
switch,
the
other
pole
may
be
utilized
to
change
the
demodulator
shift
or
other
function
as
desired.
Typical
connections
to
the
AK-1
are
shown
in
Figure
4.
6
~
f"'
•
,...,
5.
INTERCONNECTION
OF
THE
AK-1
WITH
OTHER
EQUIPMENT
Interconnection
of
the
AK-1
in
the
RTTY
system
involves
two
major
points
of
consideration:
(1)
where
the
keying
voltage
is
obtained
and
(2)
how
the
audio
output
tones
are
applied
to
the
transmitter(s).
There
are
obviously
a
great
many
techniques
that
can
be
used;
some
of
the
more
popular
forms
~re
described
in
the
following.
5.1
Keying
the
AK-1
To
key
the
AK-1
from mark
to
space
condition,
it
is
required
that
pin
6
of
the
edge
connector
be
biased
between
0
to
-15
volts
for
mark
and
+5
to
+15
volts
for
space.
Three
simple
techniques
to
derive
the
required
keying
voltage
are
illustrated
in
Figures
5,
6,
and
7
(page
20).
The
simplest,
direct
keyboard
keying
(Figure
5)
involves
addition
of
one
resistor
(4.7
K-
furnished)
between
pins
5
and
6
of
the
AK-1
edge
connector
and
connection
of
the
teleprinter
keyboard
between
pin
6
and
ground
(pins
1
and
12).
This
allows
"full-duplex"
operation
of
the
AK-1;
the
keyboard
circuit
is
entirely
independent
of
the
printer
circuit
and
both
can
be
operated
simultaneously
without
interference.
Since
this
connection
does
not
easily
allow
local
copy
of
the
transmitted
text,
it
is
not
generally
used
for
radio-communications
teleprinter
systems.
A
second
system,
shown
in
Figure
6,
is
compatible
with
most
of
the
older
tube-type
demodulators.
The
general
form
of
the
demodulator
should
be
as
shown
with
a
keyer
tube
that
normally
operates
with
a
grounded
cathode
and
with
the
printer
and
keyboard
in
series
in
the
plate
circuit.
A
voltage
proportional
to
the
loop
current
is
obtained
with
the
47
ohm
resistor
between
cathode
and
ground.
Since
these
keying
pulses
are
inverted
with
respect
to
the
AK-1
input
requirements,
the
3.9
K
bias
resistor
and
2N697
inverter
stage
are
also
required.
As
in
the
direct
connection,
a
4.7
K
resistor
is
connected
between
pins
5
and
6
of
the
AK-1.
Any
NPN
transistor
of
moderate
beta
can
be
used
for
the
inverter,
but
the
3.9
K
biasing
resistor•may
re~uire
adjustment
for
devices
other
than
the
2N697.
It
should
be
noted
that
this
circuit
will
also
work
with
any
loop
system
if
one
point
on
the
loop
can
be
grounded.
Since
the
keyboard
and
printer
are
wired
in
series,
this
connection
allows
local
copy
of
the
transmitted
text.
A
third
technique
that
will
work
with
virtually
any
low-current
loop
system
(up
to
100
rna)
is
shown
in
Figure
7.
A
HAL
FLI-1
Floating
Loop
Interface
is
used
to
provide
complete
isolation
between
the
loop
circuit
and
the
AK-1.
Developed
for
use
as
an
isolated
input
option
for
the
HAL
RVD-1002,
the
FLI-1
uses
an
optical
isolator
to
provide
coupling
of
keying
pulses
for
loop
voltages
up
to
250
volts.
The -FLI-1
can
be
purchased
separately
from
HAL
Communcations
for
$10.00.
Since
the
AK-1
was
originally
designed
to
be
used
with
the
"Mainline"
series
of
RTTY
demodulators,
interfacing
with
the
ST-5
or
ST-6
demodulator
is
very
simple.
Interconnections
between
the
AK-1
and
the
ST-5
are
shown
in
7
-•
Figure
8.
Note
that
use
of
the
two-circuit
phone
jack
for
the
CW
ID
Key
~
j",
allows
choice
of
either
AFSK
or
FSK
ID
modes
without
internal
changes
in
the
~
w1r1ng.
Connections
between
the
ST-6
and
the
AK-1
are
shown
in
the
schematic
diagram
of
Figure
9
and
in
the
cabinet
wiring
diagram
of
Figure
10.
It
is
highly
recommended
that
these
diagrams
be
followed
exactly
when
building
the
ST-6.
Factory
wired
ST-6/AK-1
combinations
with
serial
numbers
higher
•
than
#168
follow
this
connection.
When
installed
in
this
manner
in
the
ST-5
and
ST-6,
the
shift
of
the
AK-1
is
controlled
by
the
demodulator
shift
switch
and
the
AK-1
tones
are
keyed
by
anything
keying
the
demodulator
loop,
including
incoming
signals
as
well
as
by
the
keyboard.
Since
the
AK-1
tones
are
always
"on"
with
these
connections,
the
AK-1
output
is
actually
a
"regenerated"
form
of
the
input
signal
to
the
demodulator,
conditioned
and
controlled
by
all
of
the
processing
circuits
of
the
demodulator.
This
out-
put
can
be
used
to
great
advantage
with
the
ST-6
autostart
system
if
the
AK-1
output
is
recorded
on
an
audio
recorder
whose
start-stop
f~nction
is.
controlled
by
the
ST-6
autostart.
Since
the
recorded
signal
has
already
been
processed
by
the
ST-6,
any
simple
demodulator
can
be
used
when
the
tape
is
played
back.
5.2
Connecting
the
AK-1
to
the
Transmitter
There
are
two
audio
outputs
from
the
AK-1,
one
with
an
output
level
of
100
mV
rms
and
500
ohms
internal
impedance
(pin
8)
and
one
with
an
output
level
of
20
mV
rms
(pin
11)
to
drive
high-impedance
microphone-
inputs
of
transmitters.
To
avoid
hum
(and
excessive
cable
capacitance)
the
audio
cables
between
the
AK-1
and
the
transmitter
should
not
be
longer.
than
three
feet.
The
AK-1
can
be
used
to
directly
modulate
an
AM
or
FM
transmitter
to
produce
type
A2
or
F2
emissions.
This
is
the
classically
"standard"
application
of
an
AFSK
oscillator,
and
the
AK-1
generates
the
AFSK
standard
tone
convention
of
2125
Hz
mark
(lower-frequency
tone)
and
2295
Hz
(170
Hz
shift)
or
2975
Hz
(850 Hz
shift)
space
with
a
high
degree
of
accuracy.
Since
these
modes
are
authorized
for
amateur
communications
on
frequencies
above
50.1
MHz,
this
technique
is
generally
restricted
to
VHF
operations.
Either
(or
both)
output
can
be
connected
to
the
appropriate
place
on
the
VHF
transmitter
and
the
transmitter
audio
gain
adjusted
for
proper
.
modulation
level.
Note
that
some
VHF
FM
transmitters
in
particular
are
not
designed
for
continuous
transmitter-on
operation
and
may
over-heat
if
the
transmitter
power
is
not
reduced
for
RTTY
operations.
A
second
use
of
AFSK
oscillators
in
radio
communications
systems
has
been
gaining
increasing
popularity;
connection
of
AFSK
tones
to
a
SSB
transmitter
to
generate
type
Fl
FSK
emissions.
Because
of
bandwidth
restrictions,
the
only
legal
mode
for
amateur
transmission
of
RTTY
signals
in
the
3.5
to
30
MHz
frequency
range
is
type
Fl
emission.
A
standard
way
to
generate
Fl
emission
is
to
frequency-shift-key
(FSK)
an
oscillator
in
the
transmitter
system
with
the
RTTY
pulses.
A
second
technique
that
can
be
used
to
produce
a
type
Fl
emission
is
to
use
an
AFSK
oscillator
with
a
SSB-type
of
radio
transmitter.
An
understanding
as
to
why
this
"AFSK"
8
~
,...,
•
!!"'.
technique
works
and
what
some
of
the
potential
problems
are
is
the
object
of
the
following
discussion.
First,
it
is
best
that
the
basic
requirements
and
standards
of
type
Fl
RTTY
emission
for
amateur
ratio
(as
well
as
most
other
HF
services)
be
understood.
A
basic
requirement
by
the
FCC
is
that
Fl
is
"telegraphy
by
frequency
shift
keying
•.•
one
of
two
frequencies
being
emitted
at
any
instant"
-two
frequencies
maximum,
only
one-at-a-time.
(FCC
Rules
&
Regulations,
Vol.
II,
Part
2,
Section
2.201
(f),
Sept.,
1972.)
A
further
convention
for
HF
transmission
of
RTTY
signals
is
that
the
higher
of
the
two
frequencies
is
the
rest
condition
of
mark
condition.
Note
that
this
is
the
reverse
of
the
VHF
standard
of
the
lower
modulating
tone
being
the
mark
tone.
Now,
consider
the
typical
filter-type
of
SSB
transmitter
shown
in
Figure
11.
For
the
sake
of
simplicity,
it
will
be
assumed
that
no
heterodyning
of
the
original
signal
is
required
and
that
the
SSB
signal
is
generated
directly
at
the
output
frequency.
Therefore,
the
carrier
frequency,
generated
in
the
BFO
stage
is
combined
with
the
audio
in
a
balanced
modulator
to
produce
a
double-sideband
supressed-carrier
signal.
This
signal
is
then
passed
through
a
"steep-skirted"
filter
and
only
one
of
the
two
sidebands,
the
lower
sideband,
is
passed
on
to
the
amplifier
and
then
to
the
antenna.
This
sideband
generating
and
selecting
process
is
illustrated
for
a
voice
signal
in
the
spectrum
diagrams
in
Figure
11.
If
audio
tones
are
substituted
for
the
voice
signal
and
subjected
to
the
same
processing
system,
the
upper
set
of
spectra
will
be
generated
to
each
stage.
It
is
therefore
apparent
that
introduction
of
two
discrete
audio
tones
into
a
SSB
transmitter
has
resulted
in
the
generation
of
two
discrete
radio
frequencies
at
the
transmitter
output.
Also
apparent
is
the
fact
that
although
the
mark
tone
was
the
lower
frequency
of
the
audio
tones
introduced,
the
radio
frequency
produced
by
the
SSB
transmitter
from
this
mark
tone
is
higher
in
frequency
than
that
for
space
condition.
This
is
because
of
the
sideband
inversion
of
the
LSB
mode;
if
the
upper
sideband
had
been
selected,
no
sideband
inversion
would
have
occurred
and
the
radio
frequency
corresponding
to
mark
condition
would
have
been
lower
than
that
for
space.
Since
it
is
usually
desirable
to
conform
to
the
standard
of
mark
being
the
higher
frequency,
the
LSB
mode
is
generally
used
so
that
the
same
AFSK
os·cillator
can
be
used
for
both
VHF
and
HF
operations
without
an
inverting
switch.
Another
result
of
the
SSB
technique
is
that
the
frequency
of
the
mark
signal
is
not
the
same
as
that
of
the
carrier
and
therefore
the
transmitter
dial.
The
transmitter
dial
does
not
then
indicate
the
true
frequency
of
the
RTTY
signal
and
a
correction
must
be
made
to
determine
the
actual
frequency.
When
the
actual
spectrum
of
the
SSB
signal
is
considered
in
greater
detail
as
shown
in
Figure
12,
other
problems
become
apparent.
As
shown
in
Figure
12a,
the
BFO
frequency
of
a
voice
LSB
transmitter
is
placed
with
respect
to
the
filter
pass-band
so
that
the
audio
spectrum
of
300
Hz
to
2400
Hz
corresponds
to
the
-3
dB
response
points
of
the
filter.
Note
that
there
is
only
a
little
more
than
20
dB
of
carrier
suppression
contributed
by
the
filter.
Although
another
20
to
30
dB
of
carrier
suppression
can
9
reasonably
be
expected
from
the
balanced
modulator,
a
little
carrier
leakage
on
a
voice
SSB
signal
is
of
little
concern
since
single-sideband
voice
with
a
carrier
is
just
as
legal
as
single-sideband
voice
without
a
carrier.
If
the
normal
RTTY
tones
of
2125
Hz
(mark)
and
2295
Hz
or
2975
Hz
(space)
are
connected
to
the
SSB
transmitter
the
output
of
Figure
12b
results.
Obviously,
wide-shift
operation
is
out
of
the
question
if
the
filter
is
very
good
at
all
since
the
2975
Hz
output
is
down
from
the
2125
Hz
level
by
approximately
36
dB
in
this
example.
Note,
however,
that
there
is
little
differential
attenuation
between
the
two
narrow
shift
frequencies,
suggesting
that
operation
on
at
least
170
Hz
shift
is
possible.
(The amount
of
differential
attenuation
will
be
controlled
by
the
"squareness"
of
the
"corner"
of
the
filter
response
curve.)
But,
also
note
that
the
carrier
suppression
is
the
same
as
for
voice
operations.
Because
generation
of
more
than
one
frequency
at
a
time
is
contrary
to
the
FCC
defini~ion
of
type
Fl
emission,
any
carrier
that
is
radiated
is
considered
to
be
a
spurious
emission.
The
exact
definition
of
what
is
a
spurious
signal
depends
upon
many
factors
and
interpretations
but
since
they
are
all
generally
based
upon
potential
interference
to
other
users
a
good
practice
to
follow
would
be
to
assure
that
such
signals
cannot
be
heard
at
another
station.
Since
this
is
obviously
controlled
by power
level,
distance
between
transmitter
and
receiver,
receiver
sensitivity
and
a
lot
of
other
hypothetical
considerations,
the
most
practical
approach
is
to
reduce
any
spurious
signals
to
as
low a
level
as
possible.
Fortunately,
a
fairly
simple
modification
of
the
SSB
transmitter
will
allow
both
a
considerable
increase
in
the
carrier
rejection
of
the
filter
and
permit
wide-shift
operation.
The
modification
is
to
change
the
frequency
of
the
BFO
for
LSB
mode
so
that
the
RTTY
tones
are
now
centered
in
the
filter
passband.
For
a
typical
SSB
transmitter
with
a
2.1
kHz
filter,
this
amounts
to
changing
the
BFO
frequency
by
approximately
1200
Hz
from
its
voice
operation
frequency. This
procedure
is
indicated
in
Figure
12c.
Note
that
now
all
three
RTTY
frequencies
pass
through
the
filter
unattenuated
and
that
the
carrier
rejection
of
the
filter
is
greater
than
60 dB.
Proper
procedure
to
determine
the
correct
RTTY
BFO
crystal
frequency
is:
1.
Locate
the
LSB
BFO
crystal,
note
its
frequency
and
whether
it
is
lower
or
higher
in
frequency
than
the
filter.
2.
Choose a new
crystal
frequency
that
is
approximately
1200
Hz
further
away from
the
filter
center
frequency
than
the
original
LSB
crystal.
3.
Order
a
good,
commercial-quality
crystal
for
this
frequency
don't
buy
a
general
purpose,
low-cost
crystal
-
it
will
probably
drift.
An
alternate
approach
that
can
be
used
if
the
center
frequency
of
the
filter
is
known
is
to
choose
a
crystal
frequency
that
is
2550
Hz
(center
between
2125
and
2975
Hz)
away from
the
filter
center
frequency,
in
the
same
10
• I
I
~
I
"""
..
\
..
~
,
1.!"\,
•
direction
as
the
original
LSB
crystal.
Often
a
switch
or
socket
can
be
installed
in
the
transmitter
so
that
LSB
voice
or
RTTY
operation
can
be
selected
at
will.
This
procedure
will
work
well
with
most
filter-type
heterodyne
SSB
exciters.
However,
it
may
not
be
possible
to
make
this
crystal
change
in
equipment
in
which
the
BFO
crystal
frequency
is
used
more
than
once
in
the
heterodyne
scheme
or
in
some
systems
that
switch
filters
instead
of
BFO
crystals
to
change
sidebands
(some
Drake
equipment).
The
exact
form
the
modification
takes
is
up
to
the
individual
and
HAL
Communications
Corp.
assumes
no
responsibility
for
any
such
modifications.
It
should
be
noted
that
use
of
the
AFSK-SSB
system
to
generate
RTTY
signals
is
NOT
RECOMMENDED
with
phasing
types
of
SSB
transmitters
because
of
their
relatively
poor
stability.
Radiation
of
spurious
signals
is
highly
probable
with
such
equipment.
Another
AFSK-SSB
RTTY
generation
scheme
that
is
nqt
recommended
is
the
use
of
"low-tones",
AFSK
tones
of
lower
frequency.
Referring
to
Figure
12b,
it
can
be
seen
that
if
the
frequency
of
the
audio
tones
were
lowered
to
say
1275
Hz
mark
and
1445
Hz
or
2125
Hz
space,
all
tones
would
easily
pass
through
the
filter
and
modification
of
the
SSB
transmitterwould
not
be
required.
Although
this
is
at
first
very
attractive,
it
has
the
following
serious
defects:
1.
The
carrier
suppression
is
the
same
as
for
voice,
not
necessarily
desirable
as
discussed
earlier.
2.
Harmonics
of
the
lower
tones,
particularly
the
2nd
harmonics
of
1275
and
1445 Hz,
will
be
radiated
with
little
attenuation
by
the
filter.
These
harmonics
can
be
easily
caused
by
distortion
in
the
SSB
transmitter
itself.
3.
The
unwanted-sideband
suppression
of
SSB
transmitters
is
greatest
for
high
audio
frequencies
and
less
for
lower
frequencies.
4.
The
percentage-change
in
frequency
is.
much
greater,
particularly
for
wide-shift.
This
means
that
low-pass
filters
for
the
AFSK
oscillator
and
bandpass
filters
for
the
demodulator
(if
transceive
operation
is
used)
are
very
difficult
to
design
and
considerably
more
complicated.
A
relatively
simple
transmitter
modification
is
therefore
traded
for
a
complex
redesign
of
both
the
AFSK
oscillator
and
demodulator.
It
can
therefore
be
concluded
that,
if
possible,
the
BFO
frequency
for
LSB
mode
should
be
shifted
to
optimize
RTTY
operations
and
that,
if
this
is
not
possible,
the
unmodified
transmitter
can
be
operated
with
170
Hz
shift
(but
not
850
Hz
shift)
if
care
is
taken
to
check
the
carrier
suppression
often.
Use
of
phasing-types
of
SSB
transmitters
or
"low-tones"
is
not
recommended.
Another
consideration
in
the
use
of
SSB
transmitters
for
RTTY
transmission
is
that
this
equipment
has
usually
been
designed
specifically
11
for
voice
operation
and
power
supply
and
output
tube
power
ratings
may
not
handle
the
100%
duty
cycle
of
RTTY.
The power
rating
of
each
transmitter
varies
with
manufacturer,
but
few
SSB
transmitters
will
last
long
operating
at
full
power
in
RTTY
mode. The
manufacturer
of
the
transmitter
under
consideration
should
be
consulted
to
determine
proper
operating
parameters
for
100%
duty
cycle
operati3n.
A
problem
noted
with
some
SSB
transmitters
is
that
in
addition
to
placing
the
BF.O
frequency
optimally
for
voice
operation,
the
frequency
of
the
audio
circuits
has
also
been
restricted
to
300
to
2400Hz.
This
can
generally
be
cured
by
changing
the
audio
circuit
slightly
(usually
a
capacitor
th
the
coupling
circuits
between
stages)
or
by
pre-emphasis
of
the
tones.
!\As
discussed
earlier,
resistor
Rx
allows
a
limited
amount
of
space-tone
'~re-emphasis
for
wide-shift
tones.
The
proper
adjustment
procedure
would
be
to
measure
the
transmitter
power
output
for
mark
and
space
(850
Hz
shift)
and
decrease
the
value
of
Rx
until
the
two
powers
are
the
same. The
powers
at
both
frequencies
will
be
affected
by
changing
the
resistance
and
it
is
impractical
to
try
to
compensate
for
more
than
2
dB
of
differential
signal
power
with
this
technique.
No
compensation
should
be
required
for
170
Hz
shift
since
both
tones
should
be
well
within
the
pass-
band
of
the
filter.
12
•
~
If',
~"'
•
8"\.
6.
TEST
AND
ALIGNMENT
Refer
to
the
schematic
diagram,
Figure
1,
and
the
circuit
board
layout,
Figure
2,
to
locate
the
test
points
mentioned
in
the
following
procedure.
After
the
AK-1
circuit
board
and
related
connectors
and
power
supply
have
been
wired,
apply
power
to
the
oscillator
and
check
for
the
presence
of
+12
volts
de
at
pin
5
of
the
edge
connector
and
for
+8.2
V de
at
the
emitters
of
Q2
and
Q3. The
total
current
drain
from
the
+12
volt
power
supply
should
be
of
the
order
of
30
rna
±5 rna.
If
the
voltages
are
not
correct
or
if
the
current
consumption
is
wrong,
a
mistake
in
wiring
has
been
made
and
should
be
located
and
corrected
before
proceeding.
If
an
oscilloscope
is
available,
proper
operation
of
the
oscillator
and
bistable
multivibrator
(BSMV)
can
be
checked.
The
waveform
across
the
0.01
~fd
polystyrene
timing
capacitor
should
be
a
saw-tooth
of
approximately
two-times
the
desired
output
frequency
and
the
waveforms
at
the
collectors
of
either
Q5
or
Q6
should
be
square
waves
of
the
same
frequency
as
the
output.
The
waveform
at
the
base
and
emitter
of
Q7
should
be
a
sine-wave
at
the
output
frequency.
If
an
oscilloscope
is
not
available,
the
100
mV
output
of
the
AK-1
can
be
coupled
to
a
RTTY
demodulator
and
the
tones
adjusted
to
the
frequencies
of
the
demodulator.
Generally,
there
should
be
little
trouble
with
the
AK-1,
experience
has
shown
that
99%
of
problems
with
the
AK-1
can
be
traced
to
wiring
errors.
After
it
is
determined
that
the
AK-1
is
functioning
correctly,
the
frequencies
of
the
tones
should
be
checked
with
a
frequency
counter.
The
counter
should
be
connected
to
the
100
mV
output.
Note
that
some
counters
(such
as
the
Heath
IB-101)
have
a
very
high
input
impedance
and
no
blocking
capacitors.
In
this
case,
the
very
small,
but
finite,
leakage
in
electrolytic
capacitor
c9
can
place
a
de
potential
at
the
counter
input
and
cause
no
indication
or
faulty
indication.
It
is
therefore
recommended
that
the
100
mV
output
be
terminated
in
1000 ohms when
aligned
in
this
manner.
Always
adjust
the
AK-1
in
the
mark
condition
first
and
then
adjust
the
two
space
tones.
Therefore,
set
the
input
keying
signal
for
marking
condition
and
adjust
R12
and
R13
for
an
output
of
2125 Hz.
Note
that
R1
3
is
a
coarse
adjustment
and
R12
is
a
fine
adjustment
for
the
mark
tone.
The mark
tone
should
be
2125
Hz
for
either
shift.
Now
place
the
shift
switch
in
the
170
Hz
position
and
set
the
keying
input
for
a
space
condition.
Adjust
R6
for
an
output
frequency
of
2295 Hz.
Change
the
shift
switch
to
850
Hz
and
adjust
R4
for
an
output
frequency
of
2975 Hz. Check
the
amount
of
CW
ID
shift
by
returning
the
keying
signal
to
the
mark
condition
and
shorting
the
key
jack
-
the
frequency
should
shift
to
approximately
2225
Hz
in
either
position
of
the
shift
switch.
This
frequency
can
be
adjusted
by
changing
the
value
of
R8,
but
this
is
normally
not
necessary.
As
discussed
previously,
resistor
locations
Ra, Rb,
and
Rc
have
been
provided
to
allow
further
trimming
of
the
total
series
resistance
for
each
tone
if
necessary.
Experience
has
shown
that
the
ranges
of
the
13
f
t
I
I
i
potentiometers
are
sufficiently
great
to
account
for
component
tolerances
and
it
should
therefore
be
possible
to
adjust
all
of
the
tones
directly
without
changing
or
adding
resistors.
The
low-pass
filter
requires
no
adjustment.
Proper
performance
is
indicated
by
comparing
the
output
voltage
for
2125
Hz
with
~hat
of
297~
Hz.
The two
levels
should
be
within
0.5
dB
of
each
other
if
the
filter
is
performing
correctly.
As
mentioned
earlier,
resistor
location
~
is
provided
to
allow
a
small
amount
of
space-tone
pre-emphasis.
The
audio
stages
of
some
transmitters
may
tend
to
have
slightly
reduced
output
of
2975
Hz
as
compared
with
2125 Hz.
Insertion
of
a
resistor
at
Rx
forms
a
single-pole
low-pass
filter
with
C10
and
can,
in
some
cases,
provide
some
compensation
of
the
low-level
space
carrier
output.
It
should
be
noted,
however,
that
both
tones
will
suffer
some
attenuation
and
it
is
impractical
to
try
to-compensate
for
more
than
a
2.0
dB
difference
in
levels
with
this
technique.
When
the
HAL
AK-1
is
constructed
as
a
part
of
the
HAL
ST-6,
the
alignment
procedure
can
be
somewhat
modified
and
portions
of
the
ST-6
used
in
the
test.
After
it
is
determined
that
supply
voltages
and
currents
are
correct
and
that
the
oscillator
is
functioning
correctly,
connect
the
100
mV
output
of
the
AK-1
to
the
audio
input
of
the
ST-6.
Put
the
ST-6
AUTO-STAND-BY
switch
in
STAND-BY
position
and
the
LIMITER
switch
in
the
ON(FM)
position.
Connect
the
frequency
counter
to
pin
8
of
the
edge
connector
of
the
number 1
board
for
the
shift
under
test
(i.e.,
for
the
170
Hz
shift,
connect
the
counter
to
1-170(8)
and
for
850
Hz
shift
to
1-850(8)).
This
technique
has
the
advantage
that
the
input
bandpass
filter
and
limiter
stages
of
the
ST-6
serve
as
counter
input
stages,
reducing
noise,
increasing
signal
strength,
and
improving
accuracy
of
the
measurement.
With
the
controls
set
in
this
fashion
and
the
printer
jack
of
the
ST-6
unconnected
to
anything
(self-shorting),
the
AK-1
is
in
the
mark
condition
and
the
2125
Hz
tone
can
be
adjusted
as
before.
To
obtain
the
space
condition,
plug
an
unconnected
plug
into
the
ST-6
printer
jack,
opening
the
loop.
Now
adjust
the
space
tones
-
note
that
it
is
necessary
to
move
the
counter
connection
point
from
one
board
no.
1
(pin
8)
to
the
other
when
changing
shifts.
An
interesting
variation
of
this
technique
is
that
the
AK-1
can
be
used
to
check
the
center-frequency
of
the
ST-6
discriminators
by
simply
observing
the
frequencies
at
which
peaks
on
the
ST-6
tuning
meter
occur.
14
1
I
t!"'
~
't
...
•
~
' '
7.
DIAGRAMS
AND
PHOTOGRAPHS
The
schematic
diagrams,
parts
layout
and
circuit
board
photographs
are
shown on
the
following
pages.
15
I'J
:J
~
·-~
W<:'1
"""1111111
'-
+12V
~
f
--~--------------------r-----------------------~------------~----.-------_,
5 I
+l2VDC!nput
fR15
1-'
Cl'
Keying
Voltage
lnput
,_
.....
-.
Mark'
-5ta-15V
Space'
+5
to+l5V
~,:
1N4148
01
R9
Keyer
CW
ID
I 10k
10k
+8.2V
Keyer
R3
I
~
t:Ic1
I I
D3
T
101'1
lfi.I47~J:I
RIO
2.2k
RB
430k
Mark
Freq.
Adj.
(2125Hz)
]R4
Space
25k
-~
Freq.
~';(·
200 k
Adj.
(2975Hz)
(2~Hz)
RS
33k
180k
RS
R7
RA
~Ra
2 I
110
I I 9 I l!J
to
Key
for
CWID
__J
Shift Switch
51
1k
Rc
Rll
15k
Fin
Il
~;;~04
~
r
2N4871
R2l
-rC2
120
~
R22
27
Oscillator
M
Ground
Return
BSMV
0
GJ
No
Connection
Rl6
lk
R23, lBk
R24
1.2
k
•
Figure
1.
AK-1
""matic
Diagram
.j,_'
_.·
Low
-poss
Filter
Notes·
R26
220
R27
22 k
Amplifier
R25
T
R28
T
R29
lk
5.6k
470
I 0
Cl0,.0151'1 I
Rx
~~~
100
mV
RMS
Output
(Low-zl
20
mV
RMS
Output
(High-
zl
1. All resistors
l/4W
unless otherwise noted.
2. Reststors R4, R6,
~12,8Rl3
ore
25
turr:!
trimming potentiometer.
3. Resistors RA,Ra,
8Rc
ore positions
on
the
circuit
board for
additional series trimming resistors.
They
ore
not
normallyrequired
and o jumper
is
installed at
these
locations.
4. Reststor
Rx
con
be added
if
required
to
qive space-tone pre-emphasis.
This location
is
normally not used.
1
r>o
x
2.47
'lt()
) j
;..
Jrio
2
~
$''1-
[M(lCOMMUNJCATIONS
CORP.
mLJ
BOX
365,
URBANA
ILLINOIS,IleOl
OAT£
APflftOVI:O
()
-~~-~.:.._-~.:._~.:.:.....:......_.
__
~----...:.__..,___-
........_
.........
_~
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