Icom IC-471H Instruction Manual page 6

error of 40% or more. Instead, use an in-line watt meter
similar to the Bird model 43 or Sierra model 164B with
UHF cartridge. Further, when adjusting a mobile antenna,
do so with the engine running preferably above normal
idling speed. This will insure proper voltage level to the
transceiver.
As the output is quite high, avoid connecting the antenna
connector to open lines and do not transmit under
mismatched conditions. If SWR is high (more than 3), the
output power is reduced to prevent damage to the final
transistors.
The RF coaxial connector on the rear chassis mates with a
standard N-type (UG-21/U) connector.
3-5 MICROPHONE
A high quality electret condenser microphone is supplied
with your transceiver. Merely plug it into the proper
receptacle on the front panel. Should you wish to use a
different microphone, make certain it has proper output
level. Particular care should be excercised in wiring also, as
the internal electrical switching system is dependent upon
it. See the schematic for the proper hookup.
Microphone plug exploded view
Ll
3-6 CW KEY
When operating CW, connect a key to the Key Jack with
the plug supplied. The connection of the plug is shown
below.
If using an electronic keyer, observe proper polarity when
installing the key plug. Make sure that the key down
voltage across the plug is less than 0.4V DC or improper
operation will result.
Key Wiring Diagram
3-7 EXTERNAL SPEAKER
The 1С-471Н 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.
3-8 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, or you wish to record contacts
using a tape recorder connected to the headphone jack.
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.
3-9 GROUND
In order to prevent electrical shocks, TVI, BCI 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.
3-10 COOLING FAN
The rear of the PA unit is designed to provide for adequate
cooling, but with 200 Watts input the final stage produces
quite a bit of heat, and its temperature may rise during
prolonged transmissions. The fan is connected to a tem-
perature monitoring circuit which monitors the temperature
of the final stage. The fan operates as follows:
1. The fan speed is slow in the receive mode and moderate
in the transmit mode.
2. When the temperature rises to a point (50°C) detected
by the temperature monitoring circuit, the fan speed
will increase during both transmit and receive modes to
provide additional cooling.
3. If the temperature rises to a danger limit (90°C) the fan
will run much more rapidly. At this time the output
power is reduced to a half of the maximum power
(about 30 watts) and the RECEIVE INDICATOR will
be blinked for a warning until the temperature goes
under 90°C. Investigate the cause of overheating i.e.
antenna mismatching, etc. and correct the cause of the
overheating before starting to transmit again.