Sweep Timing Adjustment.6-12 - Furuno 1730 Operator's Manual

(Remember that the top rad orne fixing bolts remain untightened. They should now be
secured if the following aligninent is not necessary.)
1. Identify a suitable target (e.g., ship or buoy) at a range between 1/8 to 1/4 miles,
preferably located on or around the heading mark. To minimize errors of bearing you
should generally keep echoes in the outer half of the picture by changing the range
scale.
aCAniNG ON RADAH DE ÅRING ON Ci tAflT
Fig.6-10 Relative Bearing Alignment
(When the relative bearing of a target'measured on the
radar screen @ does not agree with that measured on the
navigation chart@.)
2. Press the
EBL
touchpad to bring up the EBL on the screen.
3. Press either of the + or - touchpad until the EBL lies direetly over the target.
4. Read the EBL bearing at the bottom left on the screen.
5. Find the relative bearing to the target from the ship's bow visually, using a pelorus.
6. Compare the bearing measured in step 4 and 5 above, and calculate the direction and
magnittide of the bearing error.
7. Remo ve the ra dorne and slightly loosen the two screws which secure the heading mark
key mounting plate. If the screws are loosened excessively, fine adjustment will be
more difficiilt.
8. Adjust the position of the heading mark key, moving to the aft (or fore) direction if the
bearing "A" is greater (or smaller) than "B", respectively.
9. After adjustment, tighten the heading mark key fixing screws securely.
10. Install the radome on the radome base assembly, being careful of its direction. The
narrower recessed part should face the bow direction. See Fig.6-7.
11. Tighten the radome fixing bolts securely.
12. As a final test, move the boat towards a small buoy and ensure that the buoy shows up
dead ahead on the radar when it is visually dead ahead.
6-11
SWEEP TIMING ADJUSTMENT
This adjustment is carried out to ensure proper radar performance, especially on short
ranges. The radar measures the time required for a transmitted echo travel to the target
and return to the source, and the received echo is displayed on the CRT based on this
time. Thus, at the instant the transmitter is fired, the "Sweep" should start from the
center of the CRT (sometimes called sweep origin).
A "trigger" pulse generated in the display unit is sent to the scanner unit through the
intercormection cable to trigger the transmitter (magnetron). The time taken by the
signal to travel up to the scanner unit varies, depending largely on the length of
interconnection cable. Du ring this period the display unit should wait before starting the
sweep. When the display unit is not adjusted correetly, the echoes from a straight local
object, e.g., a harbor wall, straight pier, etc. will not appear with straight edges - i.e., they
will be seen as "pushed out" or "pulled in" near the picture center. The range of objects
will also be incorreetly shown. Therefore, the following adjustment should be carried out
after installation.
Procedure
1. Set the unit at 0.25 nm range and adjust the
GATN
and
A/C sea
Controls properly.
2. Visually, select a straight object, e.g., a harbor wall, straight'pier, etc.
3. Adjust the "TIMING" potentiometer (VR4) so that a straight object will appear straight
with no "pushing" or "pulling" near the picture center.
Fig.6-11 Location of Preset Potentiometers
(A) improper, pulling inward (B) proper (C)improper, pushing outward
Fig.6-12 Sweep Timing Adjustment
6-12