Inovonics 705 Manual

Steam Powered Radio.Com

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

Steam Powered Radio.Com

_

.......

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

Steam Powered Radio.Com

'-.

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™

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

/

,,

,

V

-30

Figure

1

i I

8d8

(SPEC)

t_

' V

✓--

-

,-

(~os)l7

/ ,

~

s'

}'

r

I/

\

/.

,,...

V

14d8

~

~v

V s

-20

-10 OdB

INPUT

+10

V

(IOOOi,

MOO.)

\

OdB

-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

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

the

power

transformer

may

be

installed

in

either

of

two

positions

for

the

two

nominal

mains

voltages.

A

silkscreened

legend

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

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

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.

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

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

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

Inovonics 705 Manual

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