Yaesu FC-902 - Notes on Antenna Matching; Tune-up Time Limits; Shack Matching vs. Line Losses; Transceiver Protection

———
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