Furuno NX-700B - Antenna Unit (NX-7 H)

5.3 Block Description
5-14
5.3.3 Antenna unit (NX-7H)
The antenna (NX-7H) is a non-directional, magnetic field type antenna. The gain of
this unit is approximately 10 dB at 518 kHz and 490 kHz, and approximately 20 dB at
4209.5 kHz.
The circuit is comprised of two antenna coils and amplifier circuits for 4 MHz band
and MF band.
The antenna coils are arranged on orthogonally-oriented X and Y axes. The phase
difference of signals induced by them is 90 degrees. To obtain this phase difference, a
signal is composed by shifting the phase of the signal from the X and Y axes by 45
degrees in the “45 deg. Phase shift” circuit. One end of the “45deg. Phase shift” circuit
is provided with the capacitor C13 and the other end with the resistor R23.
Fig. 5.3.7 Block Diagram of Antenna unit
BPF
BPF
X
Y
518/490kHz
4209.5kHz
Q5, 6
Q5, 6
Q1, 2
Q1, 2
Q3, 4
Q3, 4
OUT
Vcc (+9V)
45deg.
phase shit
45deg.
phase shit
45deg.
phase shit
45deg.
phase shit
C13
R23
R23
C13
ANT A
ANT A
ANT B
ANT B