Furuno 841 MARK-2 manual Entering Initial Settings, Relative Bearing Alignment, Sweep Timing

5.6 Entering Initial Settings

1)At the Installation Setup 1 menu, press the cursor pad to select Key Beep. (Key Beep turns on or off the buzzer which sounds when a key is pressed.)

2)Press the cursor pad to select OFF or ON.

3)Select Hdg Sensor.

4)Select type of heading sensor connected to the radar; MAGnetic compass or GYROcompass.

5)Press the [ENT] key.

6)Select ANTENNA UNIT.

7)Select M841 when using M841 antenna unit.

Leave the menu open to complete the next several adjustments.

5.7 Relative Bearing Alignment

You have mounted the antenna unit facing straight ahead in the direction of the bow. Therefore, a small but conspicuous target dead ahead visually should appear on the heading mark (zero degrees).

In practice, you will probably observe some small error on the display because of the dif- ficulty in achieving accurate initial position- ing of the antenna unit. The following adjustment will compensate for this error, up to ± 30 degrees.

1)Identify a suitable target (for example, ship or buoy) at a range between 1/8 to 1/4 miles, preferably near the heading mark. To mini- mize error, keep echoes in the outer half of the picture by changing the range.

2)Display the Installation Setup 2 menu.

● INSTALLATION SETUP 2 ●

Select item and option by trackball.

1.Align Heading

2.Adjust Sweep Timing

3.On Hours 000019.8 H

4.Tx Hours 000016.0 H

. . . . . . . . . . . . . . . . .

Press HM-OFF to temporarily hide menu.

<Press MENU for main menu.>

3)Select Align Heading and press the [ENT] key.

4)Press the cursor pad to bisect the target se- lected at step 2 with the EBL.

5)Press the [ENT] key,

6)As a final test, move the boat towards a small buoy and confirm that the buoy shows up dead ahead on the radar when it is visually dead ahead.

5.8 Sweep Timing

This adjustment ensures proper radar perfor- mance, especially on short ranges. The radar measures the time required for a transmitted echo to travel to the target and return to the source. The received echo appears on the dis- play based on this time. Thus, at the instant the transmitter is fired, the sweep should start from the center of the display (sometimes called sweep origin.)

A trigger pulse generated in the display unit goes to the antenna unit through the signal cable to trigger the transmitter (magnetron). The time taken by the signal to travel up to the antenna unit varies, depending largely on the length of signal cable. During this period the display unit should wait before starting the sweep. When the display unit is not ad- justed correctly, the echoes from a straight local object (for example, a harbor wall or straight pier) will not appear with straight edges—namely, they will be seen as “pushed out” or “pulled in” near the picture center. The range of objects will also be incorrectly shown.

(1) Correct	(2) Target pushed	(3) Target pushed
	inward	outward

Figure 5-19 Examples of improper and

correct sweep timings

Figure 5-18 Installation setup 2 menu 37