Block Diagram Of Spu Board (Video Amplifier) - Furuno FR-2115 Service Manual

Block Diagram of SPU Board (Video Amplifier)

about
4 Vpp
VIDEO IN
Buffer
A/C AUTO : OFF
R140
A/C AUTO : ON
Q9
Gate Filter Buffer
U87 Q11, Q12
3.5V
TP9
0
1us
One-shot
U35(Gate Array)
SMPL T
1) Mixer (Q17): In A/C AUTO mode, the pulse, whose level is the same as the main bang, is mixed with the video signal.
The falling edge of the pulse is coincident with the beginning of the video signal.
2) Mixer (Q46): The output of Q17 is amplified in reverse polarity by Q28, and at the same time, differentiated and then amplified by Q27.
The output of Q27 and Q28 is mixed so that the positive video signal without ac component is obtained.
Mixer eliminates the DC component of the video signal, or outputs the ac component of the video signal.
3) Peaking (Q26): not used. To improve range discrimination on short ranges, add capacitor C228, 56 to 100 pF on the SPU board.
4) STC Curve: The STC curve is menu-selectable; "ANT HGT", INITIAL SETTING 1 and "CTR STC CURVE", INITIAL SETTING 4.
The latter is determined the STC curve near screen center, up to about 10 us.
5) STC in A/C AUTO mode (Q18): A/C AUTO works more effectively, compared with the FR-2100 series. Under heavy rain,
use AC AUTO rather than AC SEA, and reduce the gain setting.
6) Video constant (U96) : The video constant is selected in the initial setting 3 menu. Factory-setting is 3 for long range detection,
Under snow, rain, and heavy sea, select either 1 or 2.
1: Wide dynamic range. Similar echo to FR-2100.
2: Middle dynamic range.
3: Narrow dynamic range, but high visual intensity.
Mix
about 4 Vpp
(Adjust by R140)
Q17
Inverter Mix
Amp. &
Buffer
Gate
Q28 Q46 Q44, 55, 56
U56
Differential
Peaking
Q27 Q26
*not used
A/C AUTO
(From SPU Board)
about 4.2 Vpp
TP11
TP12
Gain &
A/C RAIN Buffer Echo stretch
STC
(range direction)
Control
Q66, 67 CR75 Q65 Q60 ' Q64
TP13
STC Curve
STC Buffer Amp.
Gate
Q25, 52, 53 U93
U54
STC data
STC in D/A Conv.
A/C AUTO memory
mode
U68
U35
Q18
Conv.
GAIN: -7 to 0 V
STC VR Curve Generator
U100
Q30, 32, 10, U92
A/C SEA: 0 to 5V
0 to 5 V
Ant. Height
(menu selection)
2-9
Video
Amp. Log to Linear Amp.
Contrast
Converter
Selector
Q35, Q37 U96
CR57, 59, 71, 72 Q13, 14, 21
Video contrast
(menu selection)
Echo
Gain Cont.
stretch
Gain Cont.
on/off (short range)
U95 Q34
Q19/20
*Gain reduced when
*Noise is controlled and
FTC is on.
gain lowered on ranges
up to 6 mile.
A/C RAIN: -7 to 0 V
Conv.
U100
0 to 5 V
Antenna Height vs. STC Curve
Low Antenna
4.5 V
0 V
Near STC Curve Selection
Sharp Curve (H)
4.5 V
Gentle Curve (L)
0 V
10 us
Figure 2.5 @
VIDEO
(To ARPA Board:P551 A18)
about
TP4
4.0 Vpp
Buffer Selector
RF VIDEO
(To AD Conv.)
Q22, 23, 15 U43
QV VIDEO
(From ARPA Board:P551 C19)
High Antenna
Range
Standard (M)
Range
STC Curves
FR2115-SME-10G