If Agc; Rx Att - Furuno FS-1575 Service Manual

2. IF AGC

IF AGC automatically controls the gain level of the 2nd IF Q1 with hardware. IF AGC
signal is generated on the FPGA of the T-CPU board.
• AGC initiates control from a gain level of −50 to −55dBuV in reverse gain mode.
• IF AGC is not available for the manual ON/OFF operation of AGC.
• RF gain is incorporated in the IF AGC control voltage.
4.0V
AGC Voltage at RF GAIN MAX
3.0
2.0 AGC Voltage at RF GAIN 20
1.0
-10
0
0
Fig. 7.3.8 Example of IF AGC Characteristics

3. RX ATT

RX ATT (receive attenuator) is effective in preventing the distortion of received signal
caused due to its extreme strength.
The RX ATT bypasses the 1st amplifier "Q1" of the RX board. Turning ON the RX ATT
will drop the reception gain by approximately 10dB. The RX ATT switches between ON
and OFF every time the "RF GAIN" knob is pressed.
In AM mode, the RX ATT is activated to prevent the distortion of strong signal received
automatically.
The RX ATT provides hysteresis characteristics so that the RX ATT will turn ON when
the signal reception level reaches approximately 85dBuV(30% MOD) and turn OFF
when it falls to 55dBuV.
However, even if the RF ATT automatically turns ON, "ATT" will not appear on the RT
window.
CONFIDENTIAL (internal use only)
This confidential document is used only by FURUNO authorized persons.
It is strictly prohibited to reproduce the document in whole or in part without prior written permission of FURUNO.
RF GAIN ADJ.
10 20 30 40 50
15 10 25 20 35
SSG Level / RF GAIN VR
7-47
SSB 8MHz
60 70 80 90 100
RF GAIN VR
30 35 40
7.3 Receiver Circuit
dBuV
110