Furuno FAX-410 - Manual (Page 23)

- 17 -
２ .５ Operation with external receiver
(1) External receiver
When an external receiver is used, it should have a local oscillator with very good
frequency stability. The A1 detected beat, a low-frequency output, can be
monitored with the unit when the signal is supplied through receiver jack of the
external receiver. If the signal is supplied from the speaker terminal, it is
suggested to use a dummy resistor and supply signal from both ends of the dummy
resistor. The signal enters the input terminal (EXT-IN) on the back of the unit
and should be 50mV or larger at the input terminal. When an external receiver is
of ordinary type, there will be no problem of excessive input since there is a
protection circuit inside the unit. However, if direct current is superposed, be
sure to input it through a non-polarized capacitor of about 1μF.
(2) Operation
a) Beat adjustment
When using an external receiver whose beat frequency is adjustable within a
range of ±2kHz or more by means of the beat knob, set the frequency dial so as
to maximize the deflection of the receiver’s “S” meter, and adjust the beat knob
so that the center LED of the tuning indicator of the unit is lit. When a signal
from station with ISB communication from a U.S. Navy station, e.g., Guam,
Pearl Harbor or San Francisco, is received, sometimes an adjustment of the
frequency is necessary with a variable condenser or spread variable condenser,
because the frequency may shift within a range of ±2kHz from the specified
frequency of the station.
b) Band width
When noise is low, a wide bandwidth is advantageous to have good picture
quality. However, a narrow bandwidth down to 1kHz is preferable in a noisy
condition.
c) Selection of external receiver
Refer to 1.4.1 to use an external receiver and also to return to the internal
receiver.
d) Recording
Refer to 1.3.3 for recording operations and for reverse reception. In reverse
reception, set the external receiver to the FBO, LSB or USB mode similarly.
NOTE
BFO : Beat frequency oscillator LSB : Lower side band
USB : Upper side band ISB : Independent side band