Equipment Location And Grounding L0; Antenna Considerations L0 - Yaesu FT-747GX Operating Manual

Equipment Location and Grounding
In all
base
station installations, the
GND
terminal
on the rear
panel
of
the
transceiver
should
be
connected
by a
heavy
braided
cable
to a
good earth ground. Best perfor-
mance
on all
frequencies
may require
that
the
grounding
cable be less than
l0
feet
(S
meters)
long.
All
station
equipment
should
have
its
own
grounding
cable
(independent of
signal
or
control cables), connected
to
a
common
point on the ground bus close
to
the
transceiver
or
linear amplifier
(if
used).
See
the diagram below.
Locate
the
transceiver
so that
air
can
flow
freely into the
air
intake
on the
left
side,
and
out
the rear. Avoid placing
the
trans-
ceiver on top
of
another heat
generating
device such as
a
linear
amPlifier.
Antenna Considerations
The
FT-747GX
is
designed
for
use
with
any
antenna system having
a
50-ohm
resistive
impedance
at
the operating frequency. Auto-
matic
final
protection (AFP) circuitry
is
included
to
protect
the final
transistors
by
automatically reducing power output when
an
impedance mismatch (hiSh SwR)
is
present.
With an
SWR
of 3:l
for
example, about
75olo
of full
power output
is
available.
Despite
this protection, the
transmitter
should
never
be
activated unless
an
antenna
or
dummy
load
is
connected
to
the ANT
jack.
Use 50-ohm coaxial cable
with a
proper
@eo
o
@(
C=
@rEt"€l
(type-M, PL-259) plug
to
connect
the
trans-
ceiver
to
the
antenna
or
load, and
if
SWR
is
too
high
to
permit
the
desired performance,
connect
an
antenna
tuner such as the
auto-
matic FC-757AT
or
FC-
1000 between
the
transceiver and
the
antenna. See page 12
for
interconnection information.
Receiver
Front End Protection
The receiver
front
end
in
FT-747GX
includes
a
surge suppressor and
a
lamp fuse
to
protect
the sensitive receiver
circuitry
from
high
voltage pulses (EMP)
at
the
antenna terminal,
and
a
choke
to
bypass
DC
overload.
Several
thousands
of volts
can
develop naturally
when
dry
wind
or
electrical
storms
create
an
electrostatic charge
on the
antenna elements,
and
this
ib
delivered
to
the
antenna
jack if
the
antenna
is
connected
to
the
transceiver-
In
such
a
case,
the lamp fuse may burn
out
(even
if
the
transceiver
is
turned
off at
the
time). The only sure way
to
avoid this
condi-
tion is to
disconnect
the
antenna
from
the
transceiver whenever
the
weather
is likely
to
create high voltage
on the
antenna
(the
feedline should
be
grounded
to
allow
the
charge
to
dissipate).
If
the receiver
is
found
to
have
suddenly
lost
sensitivity, inspect
the
filament
of
the
lamp fuse
(Fl00l
on the MAIN Unit).
If it
is
open, determine
the
cause
of
the
overvoltage;
eB., was
the
antenna
left
connected during
an electrical storm
or dry
windy
weather
since
you last
used
the
equipment?
To
obtain
replacement lamp fuses, ask
your local
Yaesu
ooooooO
Station Ground Connections