RCA BPA-10 Installation, Operation & Maintenance Instructions Manual

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ANTENNA

TUNING

UNIT

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Type

BPA-10

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INSTALLATION-OP~RATION-MAINTENANCE

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Printed

in

U.

S.

A.

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INSTRUCTIONS

1B-30168-3-21-46

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Title

Technical Summary

Electrical Characteristics
Tube Complement . .
Mechanical Specifications

Description

Installation

Tuning

......................................•.....................••...................

Purpose

Construction .....

Circuit

Mounting
R-F

Connecfions

Remote Metering and
Static Drain
Tower Lighting,

............

General Considerations ........

Tuning Procedure with
Tuning Procedure without

Final Check
Remote Metering Equipment

.........

.... , ....................•.......••....

.........................•.....••...............................................

...................................................................•..........

.........•...........................................................

..........•....•..................•...........................................

.. ~ .....................................................................

..

......................••....••.••...........................................

TABLE

.... , ...........................................................

....

...................

..

.................

...................................

.............

Audio

.......

R-F

Bridge
R-F

....•....

Monitoring

.......

Bridge ...................

...........•.••................................................

.................................

...........•..•

.............•..

...

......

OF

......

. •

.........

CONTENTS

........

....

........

.

...............••

.•.....

..... .............•........••..........

..........

....

.

.......................................

..

..................

. . .

...........

............

.. ..........

·.·

...........................

..••.•

........

............

......

...

.............

......

................

...........•....

·•· . .

...

....

. .

.........

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.....

...

.....

.........

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...

,

..

. : . . .

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Page

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Maintenance

Parts

List

.........

Figure

1-Type
2-Simplified
3-Coupling
4-Antenna
5-Antenna
6-Antenna

2

BPA-10 Antenna Tuning Unit (Exterior View)

................•........••••...•.

..........................•..•.•...........•.........

Circuit Diagram (K-861732)

Circuit and Tuning Unit
Tuning Unit (Interior View)
Tunin·g Unit (S;hematic M-428316)
Tuning Unit (Outline M-428610)

........... , ...............................•..........

Network

.............•.....

, ,

.......

..

ILLUSTRATIONS

(K-861757)

......

.........•............

.........................................

.........

..

...

.......

.............

............................

.....

. · .

...........................

,

•...................

...

..................

............ ..

....•.....•.

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TECHNICAL

ELECTRICAL

TUBE

CHARACTERISTICS:

Operating Limits:

Carrier Frequency • • . • • • • • . • • • • • • • • • • • • • • . • . • . . . . . . • • . • . • • . . • . • . . . • • . . . • •

Transmitting

Antenna Resistance:

Output

· Output 10 kw

Line Impedance

Antenna Reactance

Can be extended in a positive direction
direction

Monitoring Rectifier:

Output Impedance
Output

At

At
Rectified current
Frequency Characteristic

Power Supply . • • . . • • .• . • • • • • . • • • • • • • • • . • • • • • . . . . . . . . . . . . . • . • . . . • . .. . • . . . • . . . 230 volts, 60 cycles

COMPLEMENT:

Rectifier . . . . . . . . • • • • • • • • • • • • • • • . • • • • • • • • • • • • . . . . . . . . . . . • • . • . . • • • • . . • • . • . • . . • . . one RCA-5V 4G

Power

(maximum)

5 kw

or

less

. • . • . . • • • . • • . . . • • . • • . . . . . . . . . . . . . • . . . . . . . . . . . • . . . l O

or

less

. . . • . . . . . • • . . . . • • . . . • . . . . . • . . . . . . . . . . . . . . . . . . . • . . 20

••....................•....•............................

......•............

if

operating from a line

...••.......•........•..........

Level

(program

5-10-kw output . . . . . . • • . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 9

1-kw output

.........•........•••.••...•.....

level-including

.........•..•.......•........................................

.....•...••.•...•••.•..............•......

...•••••..

,

of

lower impedance than the antenna resistance.

SUMMARY

•

•...•....•••••.••.•..••••••.••..•......

.••..............................

by

the addition

bridging

Joss):

of

a series capacitor; and in a negative

.

..

to

operate into 20,000-ohm bridging load

75

ma

d.c. maximum into a maximum of l 000

substantially

540

ohms
ohms

50

ohms

+j500

flat

to l 0,000 cycles

kc

to

, . . .

to

1100

to

1100

to 350

to

-j500

1700

10

-15

kc

kw

ohms
ohms

ohms

ohms.

vu
vu

ohms

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MECHANICAL

Dimensions:

Height
Width

Depth . . . . . . . • . • . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . .

Weight

SPECIFICATIONS:

...••....•.•...••.•...•.•••••.••................•.•..•.••..•...•....•...

.•.•..•..•......••••.••..•••••.•..........................•.............

(net)

••..•••••.•.•••••••••••••••••••..........•...•.•.••.•.•••..•.•.....•.

44 inches
34 inches
23

inches

330 pounds

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4

Figure

1-Type

BPA-10

Antenna Tuning Unit

(Exterior View)

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Description

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Purpose

Type BPA-10 Antenna Tuning Equipment serves

The

double

the
vergent characteristics
transmission lines
on transmitters up

purpose

of

and

to

matching antennas

either toncentric

to

suppress·ing

of

ten kilowatts

(kw)

of
or

carrier

output

di-

widely

open -wire

harmonics

.

Construction

furnish,

to

monitoring

weather

door

a

with

is

door

protected

is

*(

if

monitoring

pro-

Ml­de-

rectifier.

enclosed in a

this equipment

of

parts

All

access

means

only

.

equipped

window

by

within

-28902-A does

Ml

metal housing

proof
affording
vided with a lock. The antenna ammeter may be read
through a circular
from lightning surges

open,ted

is
side
7488-A)
sired, audio-frequency
and rectified carrier current
indication.

ready

by

the housing. A monitoring rectifier unit

of

contained

is

*Ml-28902-B

are

front

the

at

the interior. This

to

and

door

the

in

a short-circuiting switch, which

a knob extending through the

of

the housing

program

voltage

for

remote antenna current

for

contoin

not

Installation

Mounting

mounting on a wooden

designed

The unit

form

the bottom

at
are
right

Figure 6.

Care

tion where the antenna lead

is

It

connecting the housing

heavy conductor

R-F

The antenna lead-in post
unit,
(Ml-19413-1
housing in case an

line when employed should _be
in the bottom
upper terminal

is

angle

a steel

or

of

provided

posts. Dimensions

also

to

should be taken

important

Connections

provision

and

bowl

of

of

for

by

cradle

the housing. Rear mounting strips also

permit mounting the unit on

or

is

insulator) on the left-hand side

the cabinet and connection made

coil L 1. In cases where a remote an-

given in the outline

are

installation

at

insure

to

the

to

copper

a

made

open-wire

the side flanges

of

means

select a posi-

to

be as short as possible.

will

adequate

ground

bus.

located on the

is

mounting a similar post

for

line

brought

grounding

system through a

used. Concentric

is

in through a hole

plat-

two

drawing,

of

top

of

to

up-

by

the

the

the

Circuit

this antenna tuning unit essentially con-

The circuit

of

sists
the number
schematic

series inductors (L

two
adjust independently the respective terminating im­pedances
cuit. The capacitive shunt leg, which

branches,

two

­operating

Signal energy

is

fier
coupled
energy

and

tube

a monitoring

of

connection to a remote antenna ammeter and inter-

for

relay

lock
60-cycle
rectifier filament transformer (

tenna ammeter
should be connec_ted

Remote

An a-c supply

operate

to
ing. The associated filament transformer
operation
adjusted
Terminals

power

the

Static

No
no conductive
drain

some

at

or

Tower

No
as the shunt arm

of

a single T-section low-pass filter which reduces-

elements

of

diagram,

the transmission line and the antenna cir-

of

fixed

is

frequency

for

obtained from a tuned pickup coil (

the antenna

to

rectified

is

the

located in the transmitter house. A 230-volt,

power

Metering

at

to

No

supply.

in

output

amplifier

supply

not used, terminals

is

and

230

of

the rectifying equipment

190, 210,

tap

the

and

. 2

a minimum. Referring to the

to

Figure 5, there will be observed

) which

L2

1,

a value determined

at

the station.

of

operation

loading

wave

a full-

balanced

is

. Terminals also

required

is

Tl

together

by

Audio

60

volts,

or

230

nearest the existing line voltage.

are

3

No.

are

is

the monitoring recti-

of

inductor (

circuit using an

ground

to

for

).

No.

means

Monitor1ng

cycles

for

volts

250

for

used

Drain

provision

should be mounted across the antenna horn

for

path

suitable place.

other

ground exists elsewhere, a static

to

made in this unit.

is

drain

static

Lighting

lighting

tower

complication as

to

open circuit

is

to

power

employed

common

energizing the

of

will

remote meter-

is

and

connection

frequencies.

to

by

) which

L3

).

L2

5V4G

excitation

for

provided

are

No.

and

5

a jumper.

be required

tapped

'should be

introduced

is

This

gap,

to

the
the

is

8

for

of

If

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CAUTION
VOLTAGE
ANTENNA
POWER
BEFORE
PLETED.
THROUGH
DAMAGE

REMOVE

-

PRIOR

AND

SHOULD

PROPER

DANGEROUS

IMPROPER

THE

TO

I

TRANSMITTER

THE

APPLIED

BE

VOLT

EQUIPMENT_

AND

ADJUSTMENT

HAVE

AGES

EACH

TO

TRANSMISSION-LINE

NOT

ADJUSTMENTS

TERMINATION

LINE

OF

CIRCUITS.

THE

TO

BEEN

MAY

RESULT

AND

Tuning

PLATE

THE

FULL

LINE

COM-

OCCUR

IN

6enaral

functions
concurrently,

resonate the reactive component
tenna; or,

Conditions

Although

For antenna tuning, the coil

the network used in this unit serves the

impedance matching

of

desirable

is

it

the antenna

if

to

inductive, the reactive com-

is

consider them separately.

L2

antenna tuning

and

can be used

a capacitive

of

to

two

series-

an-

5

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being absorbed into the

as

ponent' can be thought
antenna tuning coil.

the antenna impedance

portion
pedance matching function can be regarded
place between purely resistive impedances, inasmuch
the characteristic impedance

ployed are determined
to be matched, with the phase shift through the network
as
pass
zero and
of
too close to the
section,
second harmonic will not be sufficiently attenuated,

hence a value near
most suitable.
upon examination
actances
and line impedances. Referdng to Figure
a simplified circuit diagram, the reactances are:

of

Under these conditions, the values

-a parameter. Since the circuit
filter, the phase shift may be anywhere between

degrees, moking possible a wide range

-180

reactance values. However, it

or

with

the arms

of

-180

such

These

~r

~

= -

X2

~

+ - -

Xa=

of

either case, only the

In

the values

by

degree (or cut-off) point

values

low

degrees will usually be found

-90

statements will become clearer

the equations re'lating

of

the network and the antenna

of

1-

sin

1-

[

most lines

of

is

not advisable

is

phase shift

of

~cosP]

P

v'i½

is

a section

and

left,

is

reactance em-

of

the impedances

of

which

2,

P]

cos

~

p

sin

P

sin

resistive

the im-

taking

as

resistive.

a low-

of

work

to

of

that

the re-

to

shows

(1)

as

the
the

Line impedance

Antenna resistance

shift through network

Phase

=

near zero

p

=

-90

of

of

for

degrees,

reactance

these values.

It will be appreciated

degrees leads to large values

-180

or

arms since

all

the other hand, if we take

On
equations simplify to:

=

X1

+

sin

~

p

choice

that

approaches zero

p

X2=+~
Xa=-~

X2,

,

X

of

If this leads to inconvenient

can be chosen

p

a new value

the desired reactance.

for

Tuning

The

insure accurate tuning adjustment and the applica-

to

of

tion
treatment
bridge
a substitution method, also

To
tance
tuning, it
antenna
comparison, the resistances and reactances
heights
and self-supporting types

of

Procedure

of

use
this instrument will be assumed during the ensuing

of

not available, measurements can be made

is

determine the values

be

to

is

at

typical insulated towers

of

with

a radio-frequency

the tuning procedure. In

proper line matching ond antenna

for

used

essential

the operating frequency. For purposes

to

sizes

to

Bridge

R-F

bridge

be described.

to

inductance and capaci-

of

know the impedance

shown in Table

are

1

yield better values

recommended

is

cases

the guyed-mast

of

for

In

these

(2)

Xa,

or

where a

by

the

of

of

various

I.

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6

x,

X3

Figure 2-Simplified Circuit

Diagram

Xz

BOWL.

INSUI..ArOR

X-S6173Z

-

-

-

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Antenna
Height•

Electrical
Degrees

• Height

in

kilocycles

in

G

50

60
70

80

90
100
110
120
130
140

150

160
170
180
190
200

·

in electrical

X

TABLE

Self-Supporting Guyed-Mast

Type Type

R

7

9
14
20
40

60

90

175
190
165
130

82

60

40
28
23

degrees

1.016

X

10-0

jx

-jlOO

-j

70

-j

25

+ j

11

+j

35

+j

80 80

+j

90

+j

80

+J

15

-j

70

-j

85

-J

55

-J

25

5

-J

+J

25

+J

50

=

X

360.

I

Height

R

13
19
28

36

140

220
370
660

1100

550

280

180

120

80

in

8

feet

+j

+j140

+j320

+J500

+J600

+j480
+j

-J250

-J450

-J500

-J430

-J400

X

-j220

-j170

-j

-j

jx

75

28

0

0

frequency

to

be

obtained
the network hove been adjusted to the
of

the 102.5 ohms, there will ex i
pedance match between the line and the antenna re­sistance
removed

In

making these adjustments, the line should be di
connected
the input terminals
of

60

ohms hos been obtained . When measurements

show

that
antenna connected
reconnected
power

.

Calculations

ore

made to insure
not exceeded. Proper capacitors
basis

of

To

enable
inductances
L2,

it should be mentioned

ance

is

120 microhenries.

in the coil

and

the antenna reoctonce will hove been

as

a cause

and

_ the impedance

to

the input impedance

is

for

a final check before turning on .full

of

the current in the capacitive branch

information received with the

intelligent estimates

obtained

L2

.

When

the other arms

proper

st

a condition

of

loss

.

bridge

determine when the desired value

60

ohms resistive, the line may be

that

the

rot

by

topping

that

connected across

of

the tuner with the

ing

of

the capacitor

are

supplied on the

order

to

be mode

down on coi

their maximum induct-

v

alue

of

im-

.

of

the

ls

L 1

and

of

s-

is

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Substitution
antenna impedances in the equations (
of

X

,

X

1

(ng function. Examination
indicates the reoctonce necessary
ample, suppose
degree antenna
ohms

of
175 ohms in equations (2) gives the
ohms

for

To tune

only

necessary
the required
antenna reoctonce from 102.5 ohms leaves 22.5 ohms

of

the resistance components

and

X

2

reoctonce. Substitution

X

1

out

necessary

3

we

hove a 60-ohm line

with

175 ohms

,

X2

and

X3.

the antenna reoctonce in this case,
to

assume

value

of

for

of

the reactive components

of

that

this reoctonce

X

.

Subtracting the

2

the impedance m·atch-

for

resistance

of

of

1)

gives the values

tuning . For ex-

and

and

the values

value

of

is

a

80

line

a 120-

+j80

60

102.5

port

ohms

and

and

it

of
of

is

Tuning

stitution method
proper
necessary

to

change in line current accompanying the switching.

When

ment. Because it
to
a relatively

low

ment.

and a series tuning

Figure

Procedure

If

no impedance

adjustment has been obtained .

to

a resistance equal

no change occurs, the tuner

the test resistor, which will usually have a roting

power

stage in the transmitter during this adjust-

To

make the adjustment simple, a coupling circuit

3.

Without

bridge

may

arrange

is

not desirable

few

watts, connection should be made

capacitor

R-F

Bridge

is

available,

be used

to

switch the line from the tuner

to

the line impedance, noting the

to

determine when a

To

is

in

to

apply

con be used, as shown in

a simple sub-

do

this, it

proper

full

adjust-

power

of

to

LZ

c1,,c2

(AS

REQUIRED}

is

a

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Figure

3-Coupling

I

2

K-86/757

Circuit and Tuning Unit

7

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resistor position, capacitor C

switch in

the

'

With

can be tuned

Then, on switching

G.

in which capacitor
current
reactance in the antenna circuit . If
be increased, the
capacitance must
reactive;
Similarly, if the current reading
than before, the
reading

Z

than

0

to

equal

CAUTION-Remove

This method may be used

sistances simply

unknown reactance values may be determined

wise,

using a

Check

Final

Upon completing the tuning procedure as outlined in

the preceding paragraphs, the adjustments should be

checked before full power
antenna. The recommended method
scribed in the

With

· tuning unit, attach the transmission line
low-range thermal milliammeter in the ungrounded side

each end of the line.

at
vide a
current values. These values should
cent when the tuning adjustment has been correctly per­formed . Under

to

plied

Upon

of

each

measured under conditions
maximum permissible current values

three nominal frequencies

at
plates.

be

will

currents

such
should

for

again

no change

if

than before, the

less

is

there

if

;

Zo-

calibrated

following

the measuring equipment disconnected from the

readable

the line

application

the tuning capacitors

intervening frequencies, the maximum values

At

approximately

are

rearranged in the circuit.

be

the

a maximum current reading in meter

the tuner input, the direction

to

turned

be

must

C

a maximum indicates the sign

to

is

load

decreased, the

be

necessary,

is
resistance

load

no change, the

is

unused jumpers.

using a

by

condenser

paragraph.

Apply

deflection on each meter and note the

conditions, full

such

removing the millammeters.

after

fvll

of

proportional

to

found

the

capacitively reactive;

the

resonance

at

less

is

load

determine unknown re-

to

calibrated

C.

at

applied

is

sufficient

agree

power, the current through

(Cl,

full modulation. The

of

shown on the name-

are

excessive, the capacitors

be

increase the

to

capacitance must

inductively

is

load

resistive.

is

load

greater

is

;

Z

than

0

greater

resistance

load

test resistor; like-

power

for

to

is

resistance

the line

to

check

of

insert a

and

to

power

within 15

may be

C2) should be
these capacitors

those listed. If

of

if

if

is

the
the

that

by

and

de-

pro-

per
ap-

Remote

equipment
for
frequency energy
fier. The method
as
Communications Commission.

current
corresponding

is

It should be equipped with a shunt adjusted
deflections
5-ohm
pose.

minals No.

remote meter and transmitter interlock relay . Sufficient

output

be obtained
tenna

coil (

quency. A
taps on the pick-up coil and
tors (C4, C5) wh i
or

connection of these capacitors.

is

approach

selectivity of this circuit

frequency response characteristic.

sponse

db

series

d.

level of

this source, the circuit

and may be used to feed a 500-ohm

this case must be

current. It

or

only

be inserted in series with the 500-ohm transformer.

Under this condition, the direct-current

and the output level from the rectifier

dbm

tion.

Metering

The antenna tuning unit embodies the necessary

outlined herein has been approved

The remote meter should require 25

As

in

Maximum output will be secured

tuned

. Under no conditions should the current through the

c.

When an

greater

to

measuring antenna current and also furnishes audio-

full-scale deflection and should have a scale

for

of

variable

shown

5

proper

for

by

loading

} and

L3

wide

parallel.

resonance . It

to

resonance

10,

at

resistors (

approximately

desirable, therefore,

is

bridging

a 500-ohm input, a 20,000-ohm carbon resistor may

5-kw operation and to

at

Equipment

enable the installation of a remote meter

a monitoring ampli-

operation

for

remote antenna-current indication

of

of the antenna ammeter (M

that

to

both meters

shunt will be satisfactory

the schematic

by

are used

8

.

No

and

deflection of the remote meter may

adjusting the coupling between the an­inductor (
by

ch

Jumpers are provided

000

Rl,

audio

L2

tuning the latter

tuning range

may be employed singly, in series,

too

will

cycles will be

be

R4)

tor

moni

of

capable

. If the monitoring ampfifier has

load

of

the Federal

by

direct

ma

50

to

that

so

most cases, a

identical.

are

diagram

} and the monitoring pick-up

is

by

not advisable, however,

is

closely since the increasing

seriously impair the audio-

allowed

to

is

17 dbm

+

which

handling 25

of

-7

In

for

(Figure 5), ter-

connection

for

the carrier fre-

to

afforded

use

the

as

resonance, the re-

At

down

to

be used,

is

balanced

is

feed a 20,000-ohm

to

dbm

by

two

of
facilitate inter-

to

the pick-up coil

approximately

exceed

an

available

to

The

.

load

ma

negligible

is

flow

reduced

is

1-kw opera -

at

th is pur-

to

the six

capaci-

75

output

from
ground
load

direct

of

to

the

the

ma

-1

1)

I
I
I

.

I

to

4

in

The antenna ammeter shorting switch

kept closed except when readings

connections, especially the coil connector clips,

All

8

(Sl)

being taken.

are

Maintenance

should

be

should be inspected

avoid

thus
ventilation openings should be unobstructed
free circulation

regularly

undue heating

air.

of

at

insure tightness and

to

points. Screens and

such

to

permit

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Symbol

No.

Al

Cl

C2

C4

C5

C6

l2

Ll,

l3

Description

Rectifier, monitor

Copocitor

Capacitor

Capacitor,
Capacitor, 200
Capacitor, 1 000

Coil
Coil

(frequency deter-

mined)

(frequency deter-

mined)

300

mmf
mmf

mmf

47

LIST

Symbol

Ml

Rl
R2

R3,R5

R4

Tl

XI

Meter (frequency determined)

Resistor,
Resistor,
Resistor, 250 ohms, 10 W 17901 K-891887-2
Resistor, 125 ohms, 10 W 17902

Transformer

Socket, vacuum

PARTS

Stock

No. No.

69860
69864 P-32220-683 SI Switch,
42335

17898 M-415903

Dwg. No,

K-891875

See Ml-7444-C

See Ml-7444-C

P-32221-532

P-722009

T-611579-501

-5

Description

K,

6.4
90

K,

IO

V.,

250

Stock

No.

Ml-19465

See

90 W

W

amp.

30

octal 18007 K-844041-50 I

tube,

17899 K-890162-2

17900 K-890162-3

90038 K-890957-1
17897 K-900433-501

Dwg. No.

K-891887-1

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Figure

4-Antenna

Tuning

Unit

(Interior

View)

9

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AUDIO

OUTPUT

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L·3

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-,

6

---

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···-

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8

ANT.

REMOTE

-=-

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c

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AMMETER'-.,..!

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6-Antenno

Tuning Unit

Outline

11

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