If Transmitting Circuit - Furuno Felcom 250 Service Manual

1. IF Transmitting Circuit

The transmitting data signal from the MODEL board (base band: I, Q) is converted by U4
to L-Band transmitting frequency.
π
/ 4 QPSK
Fig. 11.1.3
Reference)
16QAM: 16-positions Quadrature Amplitude Modulation
A type of multi-valued quadrature amplitude modulation where 4 phases and 4
amplitude statuses are combined to create 16 different statuses to be able to transmit 4
bit (16 values) data by a single symbol.
The data volume that can be transmitted by a single symbol is larger when compared
with other digital modulation methods, and is characteristic of being able to realize
high-speed digital communication in narrow band.
π / 4 QPSK
A QPSK which alternately uses QPSKs of a phase 45 degrees (π4/ radian) rotated in a
single modulation (a single symbol).
Since it does not go through zero point during phase deviation, a limiter can be used for
receiving, and therefore it can be strong for amplitude fluctuation.
Controlling the output level:
U2 implements adjustment for the IF board output level.
Transmitting level will be adjusted based on the "TX ATT" value captured during "cable
calibration" which was executed when the power was turned on. The required TX ATT
value is the TX ATT value for when the output level is set to the maximum level. The TX
ATT value can be confirmed on the "BDE" in the Service menu of the Web MMI.
Note that the TX ATT value displayed after cable calibration is not stable, and the
displayed value will change communication is started.
16QAM
π
/ 4 QPSK constellation and 16QAM constellation
11-3
11.1 Communication unit: FB-2000