Inovonics 705 Manual

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I
I
I
I
I
/
OPERATING & MAINTENANCE
INSTRUCTION
MANUAL
MODEL
705
'FM/
FMX™
STEREO GENERA
\

Steam Powered Radio.Com
USER'S
RECORD
Model
705
-
Serial
No
......
.
Date
Purchased
.............
.
Warranty
Card
Returned?
.
...
.
Purchased
From
.....
.
.......
.
INSTRUCTION
MANUAL
MODEL
705
- I
FM/
FMX™
STEREO
GENERATOR
March,
1988
1305
Fair
Avenue
-
Santa
Cruz,
CA
95060
(408)
458-0552

Steam Powered Radio.Com
I
II
III
IV
V
VI
TABLE OF CONTENTS
FUNCTIONAL DESCRIPTION .
Introduction - Audio Pre-Processing Require-
ments - About FMX™ - Specifications - Block
Diagram - Patent Notice
INSTALLATION
Unpacking and Inspection - Mounting - AC Power
- RFI - LINE INPUT and Range Selection - Pre-
emphasis Selection -COMPOSITE OUTPUT and
Impedance Selection - Installation of FMX™
3
9
SETUP AND OPERATION . . . . 13
Panel Controls - Setup Procedure - Composite
Equalization Adjustment
CALIBRATION
Equipment Required - Visual Inspection - Strap-
ping and Presets - Power-Up - Input Gain -
Highpass Filter - Preemphasis - Filter Tuning
- Overshoot Compensation Adjustment - Crosstalk
Trim - FMX™ Plug-In Option Calibration
- Final Level Setup
CIRCUIT DESCRIPTIONS ..... .
Input and Preemphasis Stages - Filter Overshoot
Compensator - Lowpass Filter - Subcarrier and
Pilot Generation - Output Amplifier - Power
Supply - Plug-In Option for FMX™
. . 17
.. 24
APPENDIX . . . . . . . . .
31
Part Lists - Schematics - Warranty
PAGE 2

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_ .......
I FUNCTIONAL DESCRIPTION
Introduction
Inovonics' 705 is a full-featured FM Stereo Generator (or
"Stereo Coder" in European parlance) which includes the FMX™
"coverage extension" transmission system as an easily-installed
plug-in option. FMX™ was developed jointly by the Columbia
Broadcasting System (CBS) and the U.S. National Association of
Broadcasters (NAB). The system is discussed in more detail at
the end of this section.
The 705 Generator incorporates the preemphasis and lowpass
functions required in customary broadcasting practice and
features patented compensation circuitry to avoid modulation
sacrifices due to filter overshoots. FM subcarrier(s) and Pilot
are digitally synthesized for optimum and adjustment-free
operation. User adjustments have, in fact, been reduced only to
those essential for system matching; INPUT, OUTPUT and PILOT
levels. The one exception is a "COMPOSITE EQ" control which is
preset at the factory for optimum stereo separation, but which
may be readjusted to at least partially compensate for
deficiencies in other parts of the transmission system.
Audio Pre-Processing Requirements
Though overmodulation protection circuitry is included in the
705, it is anticipated that the Generator will be preceded by
some form of "audio processing" system which places a ceiling on
program peaks with specific allowances for "protection" of the
preemphasis characteristic. It is essential that this need for
"split spectrum" audio processing be understood and met.
In FM broadcasting, a high frequency preemphasis (high-end
boost) characteristic is imparted to the input program signal
prior to transmission. At the receiver a complementary
g~~m£hssi~ (high-end rolloff) network restores overall flat
frequency response. The purpose of this exercise is to reduce
the high frequency noise inevitably added in transmission. This
noise generally gets worse as the listener's distance from the
broadcasting station increases.
If a low frequency tone (300Hz) is applied to the transmitter
input at a level which yields 100% carrier modulation, a high
frequency tone (l0kHz) applied at the same level would over-
~ modulate the carrier (400% or more) because of the preemphasis
curve. Fortunately, normal voice and music program signals have
comparatively low energy at the higher frequencies, and actual
statistics of program spectral composition were taken into
PAGE 3

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'-.
account
when
the
preemphasis
characteristic
was
established
years
ago.
Nevertheless,
occasional
high
energy,
high
frequency
peaks
(sibilants,
cymbals,
etc.)
can
still
cause
carrier
overmodu-
lation,
even
when
program
peaks
are
broadband-limited
to
100%-
modulation
values.
This
is
especially
true
when
modern-day
recordings
of
contemporary
music
are
the
program
source.
A
preemphasis
network
ahead
of
a
broadband
limiter,
and
a
deemphasis
circuit
following
it,
will
deal
with
this
situation,
though
the
overall
level
will
"duck"
whenever
a
high-end
peak
occurs.
This
imparts
a
'"choppy··
sound
to
the
program
and
reduces
both
intelligibility
and
perceived
loudness.
What
is
instead
required
is
a
program
limiter
operating
as
a
dual-band
device
with
a
broadband
section
to
cope
with
normal
program
peaks
and
an
inde£endent
high
frequency
limiter
section
(with
proportionally
faster
time
constants)
to
deal
with
those
program
components
subject
to
accentuation
by
the
transmission
preemphasis
characteristic.
A
limiter
of
this
type
(now
common
in
FM
broadcasting
systems)
has
negligible
audible
effect
on
most
program
material,
while
it
provides
absolute
protection
from
carrier
overmodulation.
Overmod
protection
circuitry
within
the
705
takes
the
form
of
a
complex,
active
peak
QliEE~~
integral
with
the
filter
overshoot
compensator.
Because
of
its
unique
mode
of
operation,
a
good
deal
more
peak
clipping
may
be
tolerated
than
with
more
simple
signal
clipping
circuits.
The
705
may,
in
fact,
even
be
used
"barefoot,"
or
with
minimal
audio
pre-processing,
yet
still
yield
quite
acceptable
and
"competitive"
performance.
About
FMX™
FMX™
is
the
tradename
for
a
patented,
improved
system
of
FM
stereo
broadcasting
which
is
fully
compatible
with
the
customary
standards
and
practices
used
throughout
the
world.
This
means
that
not
only
can
FMX™
transmissions
be
received
by
existing
mono
and
stereo
receivers
with
no
performance
compromises,
but
a
new
generation
of
FMX™-equipped
receivers
can
provide
the
broadcaster
with
a
substantial
increase
in
stereocasting
coverage
(up
to
400%
has
been
claimed
by
the
inventors),
nearly
equalling
the
noise-free
coverage
of
mono
reception.
Development
of
the
Inovonics
705
Stereo
Generator
was
actually
inspired
by
Torick
and
Keller's
1983
invention
of
FMX™
(U.S.
Pat.
4,485,483),
and
the
improvements
it
implied
for
the
entire
FM
broadcasting
industry.
The
Inovonics
Generator
was
designed
from
the
beginning
to
accept
and
support
a
plug-in
circuit
card
for
the
FMX™
system,
leaving
the
"whether"
and
"when"
at
the
option
of
the
individual
broadcaster.
The
FMX™
system
employs
a
second,
"quadrature"
subcarrier
at
the
same
38kHz
as
the
regular
L-R
signal,
but
with
a
90-degree
phase
o££set.
The
additional
subcarrier
is
modulated
by
PAGE
4

Steam Powered Radio.Com
"compressed" L-R program information which is "expanded" in the
FMX™ receiver for a much-improved signal-to-noise figure.
The compression transfer function (input vs. output) of the
"quadrature" subcarrier (S') has a "reentrant" or dynamic
inversion characteristic; that is, the level of S' reaches a
maximum
value then begins to drop (even as the input continues to
increase) until it "shuts off" completely. S' shutoff is
concurrent with maximum levels of the normal stereo subcarrier
(S). Total modulation, including the L+R "mono" (M) component,
(M + S + S') should never exceed the usual 100% value of the
"interleaved" stereo signal. The FMX™ compression function is
graphed in Figure 1.
/
,,
/
-40
/
/
,,
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-30
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/ ,
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-20 -10 OdB
INPUT
+10
V
(IOOOi, MOO.)
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-10
-20
-30
-40
+10
0
u
T
p
u
T
FMX™ COMPRESSION CHARACTERISTIC
(S' compressor IN vs. OUT relative to S)
The FMX™ receiver has a dual demodulator which independently
recovers program information from both the Sand S' subcarriers.
Because both signals are always available, ··servo·· techniques may
be used in the complementary expansion process. This obviates
the perfect tracking of levels and time constants demanded by
most traditional compander schemes. Dematrixed and recovered
-~ Left and Right program channels are thus optimized for best S/N
at low levels.
PAGE 5

Steam Powered Radio.Com
The
FMX™
system
is
currently
owned
and
licensed
by
Broadcast
Technology
Partners
(BTP).
It
was
re-engineered
in
1987
to
resolve
certain
technical
issues
which
prevented
universal
acceptance
by
FM
broadcasters
and
receiver
manufacturers
at
the
time
of
first
introduction
in
1986.
The
current
plug-in-option
circuit
card
available
from
Inovonics
contains
all
updates
as
of
the
date
of
manufacture.
Furthermore,
since
FMX™
circuitry
may
be
user-installed
in
a
matter
of
minutes,
any
future
updates
are
very
easily
implemented.
Specifications
Freguenc~
ResEonse
(preemphasis
defeated):
+/-0.5dB,
25Hz-16kHz;
-20dB
or
better
at
lOHz,
-60d8
or
better
at
19kHz
.
Distortion:
<0.1%
THD
in
baseband
and
subcarrier
at
90%
modulation.
NQi~§
(below
100%
modulation,
Pilot
OFF):
-75dB
or
better
in
baseband
and
subcarrier;
38kHz
residual
and
"digital"
noise
above
54kHz,
-60dB
or
better.
Stereo
Separation:
Better
than
55dB,
25Hz-
5kHz;
better
than
50dB,
5kHz-16kHz
.
Crosstalk
(M/S
or
S/M)
:
better
than
-60dB
.
EilQt:
19kHz,
+/-lHz;
<2%
THD
(distortion
products
better
than
55dB
below
100%
modulation);
Pilot
injection
level
adjustable
between
6%
and
12%
relative
to
100%
modulation.
ln~~t~ (LEFT
and
RIGHT) :
Active-balanced,
bridging;
accept
line
input
levels
between
-15dB
and
+15dB
for
100%
modulation.
(OdB = 0 . 775V
r.m
.
s.)
In~ut
Filtering:
7-pole,
phase-corrected,
active-elliptic
"FDNR"
lowpass
with
defeatable
overshoot
compensation
circuitry.
Third-order
Chebyshev
highpass
section.
Preem12hasis:
Selectable
for
75-
or
50-
microsecond
or
"flat
··
transmission
characteristics.
PAGE
6

Steam Powered Radio.Com
-~-
Output:
Single-ended
(unbalanced);
select-
able
75-ohm
or
"zero"
(voltage
source)
impedance.
Level
adjustable
between
-5
and
+12dB
(0.5-3V
r.m.s.
or
1.
2-8V
p-p).
Overmodulation
Protection:
Integral
with
input
filter
overshoot
compensation
circuit
and
defeatable
with
same.
QigiLal
SYnLhesis
Sami;ui~
RaLe:
608kHz
(16X
subcarrier).
O~tion
For
FMX™:
User-installable
auxiliary
plug-in
circuit
board
with
all
parameters
preset.
Power
Requirement:
105-130
or
205-255VAC,
50/60Hz;
8
Watts.
Size
gnd
Y!.§J.gh,t.:
1-3;4··
x
19··
x
8"
(lU);
8
lbs.
Block
Diagram
A
simplified
block
diagram
of
the
705
Stereo
Generator
is
shown
on
Page
8.
Generator
circuitry
is
explained
in
detail
under
Circuit
Descriptions,
Section
V,
which
reference
the
complete
set
of
schematic
diagrams
contained
in
the
Appendix,
Section
VI.
fgt.§nt
Notice
Lowpass
filter
overshoot
compensation
circuitry
employed
in
Inovonics'
Model
705
Stereo
Generator
is
covered
by
U.S.
Patent
No.
4,737,725.
PAGE
7

Steam Powered Radio.Com
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Steam Powered Radio.Com
II INSTALLATION
Unpacking and Inspection
Upon receipt of the equipment, inspect carefully for shipping
damage. Should any such damage be observed, notify the carrier
at once; if not, proceed as outlined below. It is recommended
that the original shipping carton and packing materials be saved
should future reshipment become necessary. In the event of
return for Warranty repair, shipping damage sustained as a result
of improper packing for return may invalidate ~h~ Warranty.
IT IS Y~BY IMPORTANT that the Warranty Registration
Card found at the front of this manual be completed
and returned. Not only does this assure coverage of
the equipment under terms of the Warranty, and pro-
vide some means of trace in the case of lost or sto-
len gear, but the user will automatically receive
specific SERVICE OR MODIFICATION INSTRUCTIONS should
they be issued by the factory.
The Inovonics 705 is packaged to mount in a standard 19-inch
equipment rack and requires only 1-3/4 inches (lU) of vertical
rack space. The 705 generates negligible heat and, itself, is
unaffected by wide variations in ambient operating temperature.
AC Power
Unless specifically ordered for export shipment, the 705 is
delivered for operation from 125V, 50/60Hz AC mains. The
back-panel designation next to the fuseholder will confirm both
the mains voltage selected and the value of the fuse to be used.
Mains voltage reselection is easily made with the top cover
removed. A plug-on jumper strip next to the power transformer
may be installed in either of two positions for the two nominal
mains voltages. A silkscreened legend next to the connector
clearly indicates its orientation. A proper fuse must always be
installed, and the appropriate back-panel voltage designation
should be marked to indicate the input power requirement.
PAGE 9

Steam Powered Radio.Com
,
__
The
detachable
power
cord
supplied
with
the
705
Generator
is
fitted
with
a
North-American-standard
male
connector.
The
individual
cord
conductors
are
§~QQQ§~gly
color-coded
in
accordance
with
CEE
standards:
BROWN=
"hot,"
BLUE=
neutral,
GREEN/YELLOW=
earth
ground.
If
this
turns
out
IlQ~
to
be
the
case,
we
offer
our
apologies
(cord
vendors
vary)
and
advise
that
U.S.
color
coding
applies:
BLACK=
"hot,"
WHITE=
neutral,
GREEN
=
earth
ground.
REI
Though
the
705
has
been
designed
to
operate
in
close
proximity
to
broadcast
transmitters,
care
should
be
exercised
in
locating
the
unit
away
from
abnormally
high
RF
fields.
In
some
installation
situations
an
RF
ground
loop
may
be
formed
between
the
input
or
output
cable
shield
grounds
and
the
AC
power
cord
ground.
Use
of
a
"ground-lifting"
AC
adapter
should
remedy
the
problem,
though
the
chassis
must
ultimately
be
returned
to
earth
ground
for
safety,
LINE INPUT
and
Range
Selection
The
Model
705
has
electronically-balanced
(transformerless),
bridging
(10k-ohms
or
greater)
LEFT
and
RIGHT LINE INPUTS .
These
are
brought
out
to
the
rear-panel
barrier
strip
and
include
chassis
ground
connections
for
cable
shields.
Should
the
equipment
which
fggg§
the
Generator
require
output
loading,
600-ohm
terminating
resistors
may
be
placed
across
the
705
input
terminals.
The
705
accepts
"zero-reference"
program
input
levels
between
-15
and
+15dB
(0dB
=
0.775V
r.m.s
. ) .
This
30dB
input
level
range
is
divided
into
two,
more
manageable
15dB
segments
which
correspond
to
the
15dB
range
of
the
INPUT GAIN
controls
.
There
are
i~Q
sets
of
dual
jumper
strips
under
the
top
cover,
just
behind
the
LINE
INPUT
barrier
strip.
Though
the
two
positions
for
range
selection
"shunts"
are
clearly
marked
in
the
board
legend
("H"
for
HIGH
level
, 0
to
+15dB;
"L"
for
LOW
level,
-15
to
0dB),
Figure
3
shows
the
jumpering
options.
As
shipped,
the
705
is
jumpered
for
HIGH
level
inputs.
PAGE
10
BIGH
LEVEL
INPUTS
(OdB
to
+15dB)

Steam Powered Radio.Com
Preemphasis
Selection
Both
75-microsecond
(U.S.)
and
50-microsecond
(European)
FM
broadcasting
preemphasis
standards
are
readily
accommodated.
Two
jumper
strips,
each
with
a
shorting
"shunt,"
are
located
under
the
top
cover,
just
next
to
the
LEFT
and
RIGHT INPUT GAIN
controls.
The
"shunts"
may
be
installed
in
either
the
"50"
or
the
"75"
(microsecond)
positions
as
indicated
in
the
circuit
board
legend.
When
the
front
panel
PRE-EMPHASIS
switch
is
ON,
the
selected
characteristic
is
imparted
to
the
input
program
signal.
With
the
switch
OFF,
input
signals
are
transmitted
"flat,"
iii.:t.hout
preemphasis,
as
required
for
testing
or
when
preemphasis
is
provided
by
preceding
audio
processing
gear.
COMPOSITE
OUTPUT
and
Impedance
Selection
The
single-ended,
"unbalanced"
COMPOSITE
OUTPUT
of
the
705
is
ground-referenced
and
has
a
"zero"
impedance
(voltage-source)
output
characteristic.
A
75-ohm
"buildout"
resistance
is
provided,
however,
and
may
be
placed
in
series
with
the
Lo-Z
output
when
the
705
is
presented
with
complex
reactive
loads
which
might
otherwise
cause
the
output
stage
to
become
unstable.
A
short
coaxial
cable
"pigtail"
runs
from
the
rear-panel
COMPOSITE
OUTPUT
jack
to
a
connector
strip
located
beneath
the
top
cover,
between
the
PILOT
and
COMPOSITE
LEVEL
controls.
The
end
of
the
cable
may
be
plugged
onto
the
strip
in
either
of
two
positions,
labeled
"LO-Zand
"75-OHMS"
in
the
board
legend.
Figure
4
pictures
the
two
impedance
selection
options.
As
shipped,
the
LO-Z
output
is
routed
to
the
rear
panel
jack.
LOW-Z
OUTPUT
(voltage-source)
Installation
Qi
E~X™
Figure
4
75-OHM
OUTPUT
(series
resistor)
Whenever
the
705
is
used
~i:t.h.Qut
the
FMX™
option,
a "dummy
plug"
must
be
kept
in
the
FMX™
accessory
socket.
This
plug
turns
off
the
FMX™
mode
indicators
and
normalizes
internal
levels
at
the
input
of
the
subcarrier/pilot
combining
stage.
The
FMX™
option
circuit
board
is
installed
on
the
four
threaded
standoffs
protruding
from
the
main
Generator
board.
PAGE
11

Steam Powered Radio.Com
_
__._
...
Remove
the
screws
from
the
tops
of
the
four
standoffs
and
secure
the
FMX™
circuit
assembly
in
place
with
components
facing
up
and
the
ribbon
cable
"pigtail
"
to
the
left.
Remove
the
"dummy
plug"
from
the
FMX™
accessory
socket
and
insert
the
ribbon
cable
connector.
The
cable
has
been
preformed,
and
there
is
only
one
way
it
can
be
plugged
into
the
accessory
socket.
This
completes
installation
of
the
FMX™
option.
Be
sure
to
save
the
"dummy
plug";
it
can
be
stuck
to
the
inside
of
the
top
cover
with
a
length
of
masking
tape.
PAGE
12

Steam Powered Radio.Com
,-
III
SETUP
AND
OPERATION
Panel
Controls
A
brief
description
of
the
various
front
panel
controls
and
indicators
is
given
here.
The
user
is
encouraged
to
at
least
skim
this
section,
checking
that
terminology
used
here
agrees
with
his
understanding.
LEFT
and
RIGHT
INfQI
Q~IN
are
adjustments
to
accommodate
different
program
line
levels.
The
controls
have
a
15dB
range
and
cover
inputs
between
-15
and
0dB,
and
between
0
and
+15dB,
depending
on
the
position
of
the
input
gain
range
jumpers
described
on
Page
10.
(0dB
=
0.775V
r.m.s.)
The
eR~-EMPHASIS
switch
turns
ON
and
OFF
the
75-
(or
50-)
microsecond
preemphasis
curve
for
both
the
LEFT
and
RIGHT
program
channels.
Preemphasis
is
normally
imparted
by
the
Stereo
Generator,
and
this
switch
is
turned
OFF
only
during
testing,
or
in
the
unusual
event
that
preceding
audio
processing
equipment
has
a
preemphasized
(rather
than
a
proper
"flat··)
output
response.
The
OVERSHOOT
QQNIHOL
circuitry
compensates
for
the
natural
and
unavoidable
property
of
all
lowpass
filters
which
results
in
output
amplitude
over-excursions
even
when
a
complex
input
signal
_,__.
has
been
pre-limited.
This
circuit
establishes
a
maximum
value
for
input
signals
and
maintains
this
level
for
all
program
components,
effectively
eliminating
the
tendency
of
the
filter
to
overshoot
the
amplitude
constraint.
The
switch
is
turned
OFF
only
for
testing
or
as
otherwise
necessary
to
modulate
the
transmitter
in
excess
of
100%.
LEFT
and
RIGHT INPUT
CLIP
indicators
(red
LEDs)
light
when
the
program
input
signal
reaches
the
threshold
of
clipping
(actually
about
0.5dB
into
peak
clipping),
and
FILTER
QQtlf.
indicators
(green
LEDs)
show
that
correction
is
being
applied
to
the
signal
for
control
of
filter
overshoots.
The
COMPOSITE
LEVEL
control
adjusts
the
level
of
the
Stereo
Generator
output
signal
over
the
nominal
range:
-5
to
+12dB
(0.5
to
3.0V
r.m.s.,
or
1.2
to
8V
p-p).
These
figures
are
for
the
Lo-Z,
"voltage
source"
output
characteristic.
When
the
?5-ohm
buildout
resistance
is
inserted,
it
may
form
part
of
a
voltage
divider
and
somewhat
reduce
the
maximum
level
available.
PILOT
LEVEL
(pilot
..
insertion"
level)
is
adjustable
over
a
range
of
6
to
12
percent,
relative
to
100%
carrier
modulation.
The
adjusted
piiot
percentage
remains
constant
and
does
not
require
readjustment
when
the
COMPOSITE LEVEL
is
changed.
PAGE
13

Steam Powered Radio.Com
_, -
The ElkQT may be turned OFF independently of the subcarrier
for certain tests. When the Pilot is OFF in the stereo mode, a
red indicator lights. The switch is normally left in the ON
position with a green LED indicating stereo operation.
The EMX™ option is switched ON or OFF by the appropriately
labeled switch with its attendant LED indicators. When the option
is IlQ.1 included with the 705, an FMXTM "dummy plug" is kept in
the accessory socket to normalize levels and render the LED
indicators inoperative regardless of switch position.
The MQQE switch lights a green indicator during STEREO
operation and enables the PILOT and FMX™ switch functions and
indicators. When switched to MONO, all subcarrier and pilot
signals are turned OFF, and the red indicator next to the switch
is then the only one of that group which lights.
The EQNER switch does, indeed, turn the 705 ON and OFF.
§.§..11!£ Procedure
This setup procedure for the 705 Generator presupposes a
simple installation with the Generator fed directly from the
output of a properly adjusted audio processor. As explained on
Pages 3 and 4, the processor should maintain program peaks at a
ceiling value corresponding to 100% modulation, and incorporate
"preemphasis protection" (independent high frequency) limiting in
addition to broadband peak control.
The Procedure also assumes direct connection of the 705 output
to the "composite" (broadband) input of the transmitter or
exciter.
Variations from these conditions, such as an intermediate STL
(microwave link) in either the input or output path of the 705,
may require considerations not addressed here.
1. Double-check board jumpering for proper mains voltage, line
input level range, preemphasis characteristic and composite
output characteristic.
2. Set the 705 MODE switch to STEREO, PILOT switch ON, O-SHOOT
CONTROL switch ON, and PRE-EMPHASIS switch ON.
3. Feed the ~JJgiQ processor LEFT channel input with a 500Hz
sinewave test signal which yields 6 to l0dB of signal
limiting. This should drive the processor line output to its
"ceiling" value and present the 705 LEFT input with a signal
representing 100% modulation of that channel.
4. Adjust the 705 LEFT INPUT GAIN control clockwise until the
LEFT INPUT CLIP indicator comes on, then slowly back the
control down (counterclockwise) until the indicator ~~2~ goes
out.
PAGE 14

Steam Powered Radio.Com
5.
Shift
the
test
tone
to
the
RIGHT
input
of
the
audio
processor
and
verify
the
same
amount
of
peak
limiting
as
for
the
LEFT.
Repeat
Steps
3
and
4
for
the
RIGHT
channel
of
the
705
.
6.
Feed
the
processor
with
a
typical
stereo
program
signal.
A.
The
audio
processor
should
indicate
a
normal
amount
of
broadband
peak
and
high
frequency
limiting.
B.
It
is
normal
for
the
LEFT
and
RIGHT INPUT
CLIP
indicators
(red)
to
flash
on
program
material,
even
though
the
input
level
is
held
at
an
absolute
ceiling
value.
This
is
due
to
accumulated
phase
shifts
in
the
25Hz
highpass
and
30kHz
lowpass
input
filters,
as
well
as
phase
response
differences
between
the
705
active
preemphasis
circuitry
and
that
of
the
preemphasis
protection
limiter.
7.
Observing
the
station
Modulation
Monitor,
adjust
the
COMPOSITE
LEVEL
control
for
an
indication
of
100%
modulation
on
program
peaks.
8.
Also
with
the
aid
of
the
Modulation
Monitor,
set
the
PILOT
LEVEL
for
the
desired
injection
level;
typically,
8-10%.
Composite
Equalization
Adjustment
(OPTIONAL)
Provision
has
been
included
in
the
705
for
limited
equali-
zation
of
the
composite
output
signal.
The
adjustment
is
optimized
at
the
factory
for
best
stereo
separation
based
on
the
,.>~
"oscilloscope
method
"
of
measurement
at
the
705
COMPOSITE
OUTPUT
connector.
It
is
possible,
however,
to
readjust
the
EQ
to
correct
for
other
transmission
system
response
deficiencies,
either
in
the
exciter
input
stages,
in
a
Composite
STL,
or
even
in
a
lengthy
cable
run
between
the
Generator
and
the
transmitter.
If
the
frequency
and
phase
response
of
the
transmission
system
2~Z2~1
the
705
Generator
is
known
to
be
linear,
it's
best
to
leave
the
EQ
adjustment
alone!
A
procedure
for
this
adjustment
is,
nonetheless,
outlined
here.
1.
Remove
the
top
cover
of
the
Generator
and
locate
the
Composite
Equalization
Control,
R188,
the
single-turn
trim
pot
just
to
the
lgf1
of
the
PILOT
LEVEL
control.
2.
Turn
the
PRE-EMPHASIS, PILOT
and
FMX™
switches
OFF .
Feed
a
lkHz
sinewave
signal
to
the
LEFT
input
(only)
of
the
705
and
adjust
the
signal
level
for
about
90%
modulation.
It
is
important
that
there
is
no
test
signal
leakage
into
the
RIGHT
input
of
the
Generator.
PAGE
15

Steam Powered Radio.Com
3.
With
an
oscilloscope,
monitor
the
demodulated
composite
signal
at
the
appropriate
wideband
output
of
the
Modulation
Monitor.
A
short
length
of
coax
should
connect
the
Mod
Monitor
gir~Q~
to
the
vertical
input
of
the
'scope.
Do
IlQ1
use
a
'scope
probe
to
monitor
this
signal,
and
be
sure
that
the
oscilloscope
is
known
to
be
in
proper
calibration
.
Phase
shift
in
the
'scope
input
circuitry
will
result
in
improper
adjustment!
It's
best
to
externally
trigger
the
'scope
timebase
directly
from
the
audio
signal
which
feeds
the
LEFT
input
of
the
705
to
assure
a
more
stable
display
of
the
demodulated
composite
waveform
which
should
resemble
Figure
5.
4.
Increase
vertical
sensitivity
of
the
'scope
to
resolve
"flatness"
of
the
baseline.
NOTE:
some
oscilloscopes
will
show
erroneous
distortion
at
the
baseline
when
severely
overdriven.
Watch
for
an
abrupt
change
at
the
baseline
as
the
vertical
sensitivity
is
progressively
increased;
ie:
a
change
in
flatness
which
does
IlQ~
correspond
to
a
step
increase
in
the
vertical
gain
.
Keep
gain
below
such
an
overload
point.
5.
As
R188
is
rotated
from
one
extreme
to
the
other,
the
observed
baseline
should
pass
through
a
point
of
optimum
flatness
as
depicted
in
Figure
6.
6.
Increase
the
oscillator
frequency
to
15kHz
and
again
check
for
baseline
flatness.
It
should
be
possible
to
adjust
R188
for
a
best
flatness
(separation)
compromise
at
the
two
test
frequencies.
7.
Replace
the
top
cover
and
return
the
Generator
to
normal
operation.
Don't
forget
to
turn
the
PILOT,
PRE-EMPHASIS
and
FMX™
(if
used)
switches
back
ON.
PAGE
16

Steam Powered Radio.Com
--~
IV CALIBRATION
1.
EQUIPMENT
REQUIRED
A.
Dual
Trace
Oscilloscope;
2mV
sensitivity,
20MHz
bandwidth
and
two
matched
10:1
probes.
B.
Audio
Generator;
10Hz
-
1Mhz,
+20dB
output
capability
with
step
and
vernier
attenuators.
C.
AC
Voltmeter;
lmv
(-60dB)
sensitivity,
5MHz
bandwidth.
D.
Frequency
Counter;
1Hz -10MHz
range
with
1Hz
resolution.
2.
VISUAL INSPECTION
A.
Inspect
the
board
for
general
workmanship
and
to
verify
polarized
components
installed
properly.
All
ICs
should
be
facing
the
rear
of
the
chassis.
B.
Check
that
the
Voltage
Selector
is
positioned
for
the
mains
supply
to
be
used,
and
that
an
FMXM
"dummy
plug"
is
inserted
in
the
Jl
socket.
3 .
STRAPPING
AND
PRESETS
A.
Set
all
front
panel
slide
switches
OFF
and
turn
all
front
panel
controls
fully
CCW.
B.
Center
all
single-turn
circuit
board
trimpots.
C. Move
Input
Gain
Jumpers
to
"L
··
and
Preemphasis
Jumpers
to
··
75";
Output
Characteristic
Selector
to
"LO-Z."
4.
POWER-UP
A.
Turn
POWER
ON
and
check
the
+/-15
volt
and
+/-6
volt
supplies.
The
left-hand
end
of
the
four
diodes
next
to
the
regulator
ICs
are
convenient
test
points.
B.
Monitor
the
"clock"
at
TP9
with
a
'scope
probe
for
a
12
volt
p-p
squarewave.
Transfer
the
probe
from
the
'scope
to
the
frequency
counter
and
trim
C57
for
exactly
1216.000kHz.
With
the
probe
reconnected
to
the
'scope,
turn
POWER
on
and
off
several
times
to
ensure
that
the
clock
starts
every
time
without
hesitation.
PAGE
17

Steam Powered Radio.Com
~-·--.
5.
INPUT GAIN -HIGHPASS
FILTER
-PREEMPHASIS
A.
Monitor
TP5
and
TP6
with
probes
connected
to
the
A
and
B
channels
of
the
'scope.
Apply
a
lkHz
oscillator
signal
at
-l0dB
to
both
the
Left
and
Right
Line
Inputs,
single-ended,
using
the"+"
terminals
and
Ground.
The
two
'scope
traces
should
each
show
a 2
volt
p-p
signal.
B.
Observing
the
'scope
traces,
momentarily
short
the"+"
terminal
of
each
input
to
its
companion
··
- "
terminal.
In
each
case
the
waveform
should
disappear,
indicating
rejection
of
the
induced
common-mode
signal.
C.
Reinstall
the
four
Input
Gain
Jumpers
in
the
"H"
position.
The
'scope
waveforms
should
drop
to
0.5
volts
p-p
.
Repeat
the"+"
to"-"
common-mode
check.
D.
Superimpose
the
two
'scope
traces
to
form
a
single
apparent
trace.
If
necessary,
adjust
one
of
the
INPUT
LEVEL
controls
to
equalize
amplitude,
and
trimpot
R47
to
equalize
the
phase
between
the
two
signals.
Sweep
the
oscillator
frequency
upward
from
lkHz;
the
traces
should
remain
superimposed
with
flat
amplitude
response
to
abotlt
12kHz
(with
filters
unadjusted).
Sweeping
the
oscillator
frequency
downward
from
lkHz
should
show
flat
frequency
and
phase
response
to
25Hz,
the
amplitude
dropping
abruptly
below
20Hz.
E.
Turn
PRE-EMPHASIS
ON
and
again
sweep
the
oscillator
upward
from
lkHz.
The
traces
should
remain
superimposed
and
increase
to
2
volts
p-p
at
l0kHz.
With
the
oscillator
set
at
l0kHz,
change
the
Preemphasis
Jumpers
to
"50";
the
p-p
amplitude
should
drop
to
1.4
volts.
Leave
the
Preemphasis
Jumpering
set
for
the
transmission
characteristic
to
be
used,
but
turn
PRE-EMPHASIS OFF
for
the
remainder
of
checkout.
6.
FILTER
TUNING
A.
Apply
a
lkHz,
0dB
signal
to
both
Line
Inputs("+"
and
Ground)
and
monitor
TP5
and
TP6
with
the
'scope.
Increase
Left
and
Right
INPUT GAIN
for
a 6
volt
p-p
waveform
on
each
trace.
B.
Set
the
oscillator
frequency
to
exactly
19,ll0Hz
and
adjust
R118
and
R141
for
nulls
in
both
channels.
C.
Set
the
oscillator
to
exactly
21,780Hz
and
adjust
R124
and
R147
for
nulls.
D.
Set
the
oscillator
to
exactly
34,570Hz
and
adjust
Rl12
And
R135
for
nulls.
PAGE
18

Steam Powered Radio.Com
7 .
OVERSHOOT
COMPENSATION
ADJUSTMENT
(Continuation
of
FILTER
TUNING
procedure.
Follows
previous
steps
directly
with
identical
setup.)
A.
Turn
trimpots
R55
and
R83
fully
CCW.
Turn
O-SHOOT
switch
ON
and
apply
l00Hz
to
both
inputs
at
a
level
that
causes
the
two
red
INPUT
CLIP
LEDs
to
just
come
on.
Balance
INPUT
GAIN
controls
for
equal
sensitivity.
B.
Increase
the
oscillator
output
level
by
exactly
10dB.
The
monitored
points
should
show
squarewaves
of
about
8
volts
p-p
.
Using
the
'scope
variable
attenuators,
set
the
two
waveforms
to
exactly
3
divisions
p-p
with
the
top
and
bottom
"flats"
precisely
on
the
graticule
divisions.
C.
Increase
the
oscillator
frequency
to
about
3.lkHz,
fine-tuning
for
maximum
amplitude
of
the
"double-hump"
waveform(s)
.
While
continuing
to
fine-tune
the
oscillator
frequency
for
maximum
amplitude
,
adjust
R47
and
R75
so
the the
left-hand
"hump"
at
the
top
of
each
trace
is
the
same
distance
below
the
upper
graticule
division
as
the
right-hand
"
hump"
is
above
it
.
D.
Increase
the
oscillator
frequency
to
15kHz
and
adjust
R55
and
R83
for
exactly
3
divisions
p-p.
FOLLOWING
THIS,
RESET 'SCOPE
ATTENUATORS
TO
THEIR "CAL"
POSITIONS.
8.
CROSSTALK
TRIM
A.
Connect
the
COMPOSITE
OUTPUT
of
the
705
Generator
gir~£11Y
to
the
vertical
input
of
the
'scope
using
a
short
BNC-to-BNC
cable.
Apply
a
lkHz,
+l0dB
oscillator
signal
to
both
Line
Inputs("+"
and
Ground).
Reduce
the
INPUT GAIN
controls
until
the
red
INPUT
CLIP
LEDs
just
come
on,
then
lower
the
oscillator
output
to
+?dB.
The
COMPOSITE
OUTPUT
waveform
should
be
a
0.8
volt
p-p
sinewave.
B.
With
the
MODE
switch
in
STEREO ,
but
with
PILOT
OFF ,
advance
the
COMPOSITE
LEVEL
for
exactly
1
Fine-adjust
one
INPUT GAIN
control
to
minimize
(38kHz
component)
riding
on
the
waveform
.
turned
volt
p-p
.
I I I I
grass
C.
Reconnect
the
Line
Inputs
to
feed
the
two
channels
out-of-phase
.
Jumper
the"+"
terminal
of
the
Left
Channel
Line
Input
to
the
..
_
..
terminal
of
the
Right
,
and
strap
the
"+"
terminal
of
the
Right
Channel
to
Ground.
The
Composite
Output
should
now
show
a 1
volt
p-p,
38kHz
DSB
waveform
modulated
by
the
1kHz
input
signal.
PAGE
19