Icom IC-R71A Instruction Manual page 6

3-4 ANTENNA
The antenna plays a very important role in radio com-
munication. If the antenna is inferior, your receiver cannot
give you the best performance. With a good antenna and
feeder cable having 50 ohms impedance, you should easily
get the desired matching and performance. Carefully install
a high performance antenna that suits the frequency band(s)
you wish to operate on and place it as high as possible. Be
especially careful of the condition of the connectors as
loose connections will deteriorate the performance.
Since the IC-R71 is a general coverage receiver it is recom-
mended that a long-wire general coverage antenna and an
antenna coupler be used. To attempt to use a Ham band
antenna for general coverage reception could result in
mismatching, and attendant poor reception. However, it is
good enough for strong broadcasting stations. Also, the
supplied antenna wire can be used as a temporary antenna.
Example of various antennas:
e Long Wire Antenna
30 - 60 feet (10 - 20m)
insulator Insulator
30 feet or more
Antenna wire a Insulator
Antenna wire
\ Soidered
"~\ \
50/75 ohm coaxial cable Outer braid
m Frequency (MHz) Frequency (MHz)
e Multiband Antenna
L1, L2 and L3 can be
calculated by the same
formula as for dipole
antenna.
Use insulators
to make each
section shorter
than L3/2
coaxial cable
3-5 GROUND
In order to prevent electrical shocks, and other problems,
be sure to connect a heavy wire ground, as short as possible,
from a good earth point to the ground terminal on the rear
panel.
Example of various ground systems:
Ground wire
City water pipe
(lead type)
Copper plate Copper rod
3-6 EXTERNAL SPEAKER
The IC-R71 contains an internal speaker, and is also
designed so that it can drive an external speaker from the
external (EXT) speaker jack on the rear panel. Be sure the
impedance of the external speaker is 8 ohms, and remember
that with the external speaker connected, the internal
speaker is disabled.
3-7 HEADPHONES
Any good headphone set, including stereo type, that have
4-16 ohms impedance can be used. With the plug inserted
halfway into the PHONES jack, both the headphone and
speaker will operate. This is convenient when others wish
to listen in-on the station.
With a stereo headphone set inserted this way, however,
the headphone will lose the sound on one side. With the
plug inserted completely, only the headphone works.
3-8 CAUTIONS
As the unit has already been closely adjusted with highly
sophisticated measuring instruments, never tamper with the
turnable resistors, coils, trimmers, etc.
C-MOS is used in the Logic unit as well as the PLL. C-MOS
ICs are very susceptible to excessive static charges and over-
current and care must be used when handling them. There-
fore, avoid touching the Logic unit and the nearby circuitry
unless absolutely necessary. When it is necessary to check
the circuitry, observe the following points.
Ground all measuring instruments, the soldering iron, and
other tools. Do not connect or disconnect the C-MOS IC
from its socket, or solder it when the power is on. Do not
apply voltage of less than —0.5 or more than +5 Volts to
the input terminals of the 1C. DO NOT MEASURE WITH
AN OHMMETER.