Furuno 851 MARK-2 - Manual (Page 29)

3. ADJUSTMENT
3-6
3.6 Sweep Timing
This adjustment ensures proper radar performance, 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 display 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 adjusted 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
inward (3) Target pushed
outward
Figure 3-8 Examples of improper and correct sweep timings
1. Display the Installation Setup 2 menu and select Adjust Sweep Timing by
pressing omnipad.
2. Transmit the radar on the shortest range.
3. Visually select a straight echo (harbor wall, straight pier).
4. While looking at the target selected above, press omnipad at the 9 o’clock or 3
o’clock position to straighten the target.
5. Press the [ENT] key.
6. After adjustment press the [MENU] key and turn off the power to close the
installation menu.