Yaesu FC-902 User manual

INSTRUCTION
MANUAL
FC-902
YAESU MUSEN CO., LTD.
TOKYO, JAPAN

THE FC-902 ANTENNA COUPLER
The FC-902 antenna coupler is designed for low and medium power
applications in the HY amateur bands from 160 through 10 meters.
It is designed to minimize the adverse effects of high SWR on a coaxial
line or wire antenna which may result in difficulty in tuning a transmitter
designed to work into a resistive 50 ohm load.
The FC-902 comes equipped with three UHF-type female coax receptacles,
and a threaded terminal to accept a single-wire antenna.
The front panel controls include a bandswitch for selecting proper
impedance values for matching, TUNE and LOAD controls for adjustment
of the capacitive coupling, and a POWER & SWR switch for setting
the meter sensitivity for the power being used. The ANT SELECT
switch chooses among any of four antennas to be matched, and if it
is desired to feed an antenna directly through the coupler to the trans-
mitter without any matching done by the coupler, a position of the
BAND switch will accomplish this.
High-quality low-loss components are used throughout the FC-902
antenna coupler, and-the matching function it performs means your
transmitter will always ''see"' the resistive termination it was designed
for. The inherent selectivity of the FC-902 matching circuitry helps
attenuate harmonics, too, thus reducing harmonic-related TVI or
out-of-band emission,

FC-902
SPECIFICATIONS
FREQUENCY COVERAGE
Input impedance
Max. variation in load
impedance
Maximum
transmitter
power
Power
meter
calibration
scales
Insertion loss
Rear
panel
antenna
connections
Dimensions
Weight
SWR calibration
160mL
1.8-2.0
MHz
160mH
1.9-2.4
MHz
80m
3.5
-4.0
MHz
40m
7.0-7.5
MHz
30m
10.0-10.5
MHz
20m,
14,0-14.5
MHz
lim
18.0-18.5
MHz
15m
21.0-21.5
MHz
12m
24.5-25.0
MHz
10m
28.0-29.7
MHz
50-75
ohms
50 ohm in: 10-250 ohms
75 ohm in: 18-300 ohms
500 W PEP @ 50 ohms
25 W, 250 W, 500 W
0,5 dB max.
3 coaxial "UHF" type
1 single wire terminal
208 (L.)x152(H)x324(D) mm.
6.5 kg.
To 4:1SWR

FRONT PANEL CONTROLS
TUNE
The TUNE control is a dual capacitor to provide capacitive adjustment
of the coupling between the transmitter and the impedance established
by the BAND switch and the LOAD control, The TUNE and LOAD
controls are adjusted for minimum SWR.
BAND switch
The BAND switch selects the inductance required to accomplish
matching on the band in question, The operator should select the
BAND switch position which best covers the portion of the band
being used, The DIREGT position of the BAND switch connects the
transmitter directly to the antenna, bypassing the FC-902 matching
circuitry, but permitting measurement of the SWR on the line at
that point.
SWR SET
This control is used to calibrate the SWR METER: the SWR may
be read accurately by adjusting the SWR SET control for full deflection
of the FWD POWER meter with the POWER & SWR switch in the
SWR SET position.
LOAD
The LOAD control is connected to a variable capacitor which adjusts
the coupling between the antenna feedline and the impedance presented
by the BAND switch inductor and the TUNE control.

ANT SELECT
This switch selects the antenna to be matched. The operator
has the choice of one of three coax-fed antennas or a single wire
antenna.
POWER &SWR switch
This switch is used to select the proper sensitivity of the FWD POWER
raeter for the power being used, and to provide calibration for the
measurement of SWR,
FWD POWER meter
The FWD POWER meter reads the output power on three scales of
25 watts, 250 watts, and 500 watts maximum.
SWR meter
When calibrated, this meter provides accurate measurement of SWR
for purposes of adjusting the LOAD and TUNE controls for the best
match,
CM COUPLER UNIT
2500)
(500)

REAR PANEL CONNECTIONS
ANT 1, ANT 2, ANT 3
These three female UHF -type connectors will accept the coaxial
feedline from the antenna. As well, a dummy load such as the
YAESU YP-150 may be attached to one of these connectors for
tuning or test purposes.
WIRE
This threaded terminal accepts a single-wire antenna such as the
"Windom" type.
GND
This terminal should be connected to a good earth ground so as to
provide a DC path to ground for stray currents, and to reduce
“RF in the shack" and ground loops, etc., that may make antenna
matching difficult. This is particulary important in the case of
certain types of single-wire antennas.
INPUT
The INPUT connector is another female UHF receptacle for connection
between the FC-902 and the RF output connector of the transmitter
or transceiver,
COAXIAL CABLE
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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

———
5)
Once
the
initial
procedure
has
been
followed
to
yield
a
near-
perfect
match,
the
POWER
&
SWR
switch
may
be
placed
in
the
position
which
most
closely
corresponds
to
the
transmitter
output
power
expected.
The
transmitter
may
then
be
adjusted
for
full
power
(some
adjustment
of
the
transmitter
load
and
tune
controls
may
be
necessary
during
matching
adjustments),
and
the
FC-902
LOAD
and
TUNE
controls
may
be
adjusted
to
yield
zero
deflection
of
the
SWR
meter.
When
the
POWER
&
SWR
switch
is
not
calibrated
with
the
SWR
SET
controls,
the
SWR
meter
will
not
accurately
read
the
SWR,
but
it
will
indicate
minimum
reflected
power.
NOTES
ON
ANTENNA
MATCHING
1)
It
is
very
important
that
the
maximum
time
limits
during
tune-up
conditions
for
the
transmitter
are
not
exceeded.
This
is
particularly
important
when
the
transmitter
is
being
used
at full
power.
2)
It
should
be
noted
that
any
matching
performed
by
the
FC-902
in
the
shack
will
have
no
effect
on
the
losses
due
to
SWR
on
the
coaxial
line
between
the
FC-902
coupler
and
the
antenna,
The
operator
should
consult
one
of
the
popular
antenna
handbooks
to
determine
whether
or
not
matching
between
the
coaxial
line
and
the
antenna
must
be
performed
at
the
antenna.
For
exemple,
a
100-foot
length
of
RG8A/U
coax
typically
has
a
loss
(with
1:1
SWR
between
it
and
antenna)
of
less
than
1
dB
at
21
MHz.
Lf
this line
is
operated
with
a
3:1
SWR
due
to
a
low
or
high
antenna
impedance,
the
loss
due
to
SWR
will
increase
roughly
0.5
dB,
an
imperceptible
degradation
as
compared
to
the
1:1
condition.
In
this
case,
attempts
to
reduce
the
3:1
SWR
at
the
antenna
end
would
serve
no
useful
purpose
as
far
as
reducing
losses
in
the
coax,
through
matching
with
the
FC-902
would
improve
the
ance
presented
to
the
transmitter
output
cirenitry.
However
if
a
500-foot
length
of
the
above
cvax
were
used
instead
of
only
100
feet,
somewhat
more
than
1dB
of
loss
would
occur
in
the
coax
due
to
the
3:1
SW,
possibly
justifying
further
matching
attempts
at
the
anteara,
3)
Whea
using
a
transceiver
such
as
the
FT-301D
which
has
protection
for the
output
transistors
against
high
SWR,
it
can
be
seen
that
the
matching
action
of
the
FC-902
will
ensure
that
a
59
ohm
load
is
presented
to
the
output
circuitry,
thus
ensuring
full
transmitter
power.
4)
It
may
be
useful
for
the
operator
to
record
in
a
notebook
the
proper
TUNE
and
LOAD
positions
for
a
particular
anteana
for
qaick r
fabricate
reace,
Alternatively,
apptopriate
labels
may
be
and
applied
2o
the
FC-902
front
panel
showing
the
tions
of
the
TUNE
and
LOAD
controls.
proper pt

PARTS LIST
al
2
DIAGRAM

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