Yaesu FC-902 - Antenna Matching Procedure

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The

reader

is

referred

to

Fig.

1,

which

contains

the

approximately

correct

positions

of

the

BAND,

LOAD,

and

TUNE

controls

for

a

50

ohm

load

impedance,

such

as

that

presented

by

a

dummy

load.

A

dummy

load

is

extremely

useful

for

tuning

up

a

transmitter

in

preparation

for

adjustment

of

matching

of

an

antenna.

If

the

control

positions

shown

in

Fig.

1

are

utilized

in

conjunction

with

a

50

ohm

dummy

load,

only

very

minor adjustments

of

the

TUNE

and

LOAD

controls

will

be

necessary

for

a

perfect

match.

Of

course,

a

50-ohm

dummy

load

should

require

no

matching

for

a

perfect

match

to

a

50-chm

transmitter

output,

but

this

information

is

presented

because

the

control

positions

in

Fig.

1

represent

useful

starting

points

for

matching

unknown

impedances.

‘The

following,

then,

is

a

step-by-step

procedure

to

follow

for

the

matching

of

an

antenna

feedline

that

has

not

been

matched

previously.

1)

Tune

up

the

transmitter

in

the

normal

way

into

a

50-ohm

dummy

load

(if

50

ohm

coax

is

used

between

the

transmitter

and

the

FC-902)

or

other

resistive

50

ohm

termination.

Reduce

the

gain

control

on

the

transmitter

to

a

minimum,

and

place

the

transmitter

in

"standby"

for

the

moment,

2)

Place

the

BAND,

LOAD,

and

TUNE

controls

in

the

positions

indicated

in

Fig.

1

for the

frequency

at

which

the

line

is

to

be

matched.

Place

the

ANT

SELECT

switch

in

the

position

which

corresponds

to

the

rear

panel

connector

of

the

antenna

to

be

matched.

Place

the

POWER

&

SWR

switch

in

the

SWR

SET

position,

and

place

the

SWR

SET

knob

in

the

12:00

position.

3)

It

is

desirable

to

make

preliminary

matching

adjustments

with

as

little

transmitter

output

power

as

possible.

Place

the

transmitter

in

the

"transmit"

condition,

and

slowly

advance

the

output

level

until

deflection

of

the

FWD

POWER

meter

is

observed.

Adjust

the

SWR

SET

control

to

line

up

the

meter

needle

of

the

FWD

POWER

meter

with

the

SWR

SET

position

at

the far

right

end

of

the

FWD

POWER

meter,

using

the

minimum

power

necessary

to

accomplish

this.

With

the

needle

in

the

SWR

SET

mark

of

the

FWD

POWER

meter,

the

SWR

meter

will

accurately

read

the

SWR.

4)

Adjust

the

TUNE

control

for

minimum

reading

on

the

SWR

meter.

If

necessary,

adjust

the

SWR

SET

control

and/or

trans-

mitter

power

to

ensure

proper

calibration.

Once

the

"dip"

has

been

found

using

the

TUNE

control,

move

the

LOAD

control

either

to

the

left

or

right,

by

a

small

amount.

Adjust

the

TUNE

control

for

a

"dip"

again,

and

if

the

SWR

improves

(again,

make

sure

that

you

are

reasonably

well

calibrated)

move

the

LOAD

control

slight-

ly

more

in

the

same

direction.

Again

"dip"

the

TUNE

control,

and

continue

this

procedure

until

no

further

improvement

is

noted.

If

the initial

direction

of

adjustment

of

the

LOAD

control

worsened

the

SWR,

move

it

an

equal

direction

from

the

starting

point

IN

THE

OPPOSITE

DIRECTION

and

follow

the

above

procedure

with

sive

adjustment

of

the

TUNE

and

LOAD

controls.

suce

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