Furuno DSC-60 - Low Sensitivity of the Receivers

7-11
2.5 Low sensitivity of the receivers
1. Press [3/TEST/DEF] key, and execute the daily test. If the test results of RX is “NG”, refer to Page
5-3.
2. Check the jumper wire setting, J3, on RX board.
When connecting FAX-5, an active antenna, DC 12 V must be supplied the preamplifier inside the
antenna unit. Set “J3” at ACTIVE side on both RX boards: DSC watch keeping receiver and general
watching receiver. Refer to Page 4-21.
Reference-1)Reference-1)
Reference-1)Reference-1)
Reference-1)
There is no problem about the receiver sensitivity if the test result is OK. The level of 18 MHz test
signal is equivalent to SG output of about 0 dBuV.
The following method can be used as a guide for on-site diagnosis of failures. No receiving signal is
required.
1. Measure the LINE OUT levels of RX boards; DSC watch keeping receiver and general
watch keeping receiver in same frequency band, and compare them. If the one is lower than
the other, its RX board or antenna is faulty.
2. Exchange the two antennas each other, and compare the LINE OUT levels in the same way. If
the output level of RX board with the previous lower level does not change. The RX board is
faulty, and if the output level rises, its original antenna is faulty.
Reference-2)Reference-2)
Reference-2)Reference-2)
Reference-2)
With Antenna disconnected: Level at TP-6 of RX board, noise level is 100 to 200 mVpp.
With Antenna FAX-5+2.6m connected: Level at TP-6 of RX board, noise level is 500 mVpp to
1 Vpp.
Antenna input level vs. LINE OUT levelAntenna input level vs. LINE OUT level
Antenna input level vs. LINE OUT levelAntenna input level vs. LINE OUT level
Antenna input level vs. LINE OUT level
2. Countermeasures against Various Failures
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0.1
0.2
0.4
0.3
0.5
0.6
0.7
0.8
0.9
1.0
-20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120 130
(Vrms)
(dBuV)
0
10
20
30
40
DISTORTION
(dBm)
ANTENNA IN
AF OUT:TP-6