Magnetron Heater Voltage Adjustment; Measurement Of Blind Shadow Sectors - Furuno 1830 Operator's Manual

MAGNETRON HEATER VOLTAGE ADJUSTMENT
Mflgnfitron
henter
voltage is formed
at the
MD board
of the
Scanner Unit
and
preadjusted at the factory. Therefore no adjustment is required even
though the cable length between the Display Unit and the Scanner Unit is
changed. Execute the following procedure to confirm.
Procedure
1-
Suspend
the
antenne rotation
by
turning off (downward)
the SCANNER
switch located at the rear panel of the Display Unit.
2. Connect a multimeter, set to lOVDC range, between #4 ft) and #6
(-)
of
test point TP803 on the MD board. See Fig.20.
3. Confirm that the multimeter shows 7.5V O.lV. If not, adjust
putentiuiiieter VR801 (Fig,20) on the MD board.
MEASUREMENT OF BLIND SHADOW SECTORS
In some shadow sectors. it should be remembered Ihat there may not be
sufficient intensity to obtain an echo from very small targets even at close
range, despite the faet that a large vessel may be detected at a mueh
greater range
in
non-shadowed sectors. For
theso
rcaoono the
an gular
width and relative bearing of any shadow sectors should tae determined.
This section describes how to do this. In the case of a new vessel this
should be done during sea trials. In other ships it should be done at the
first opportunity after fitting a new radar set.
It should be reahzed that even a small shadow sector may hide another
veasel if ahe is on a collision course. The bearing will remain constant in
the shadow area and the approach of the other vessel may remain undetected
until it is too late to avoid a dangerous situation.
Two methods of determining the angular width of a shadow sector are;
1) Turn the boat very siowly through 360" while a small but clearly defined
target is ubserved at a distance uf a udle or su, (Du not use a buoy wlth a
reflector as this target is too powerful to achieve the required result.)
If the echo disappears while the boat is turning, the target has entered a
shadow sector and it will again become visible when the target emerges from
the shadow. Very quiet conditions of wind and sea are essential to ensure
reliable results when this operation is carried out on a small eraft since a
rough sea can cause a buoy to be lost in tne dutter or to be lemporarily
submerged or hidden by waves. An unsteady movement may cause the boat
to swing through a shadow sector before the scanner has completed one
revolution. In any case an average nf several observations of
each
shadow
sector should be taken. It is a waste of time to attempt the operation in
anything other than very sinooth water with Httle wind.
2) Another method is to observe the shadow sector against a background of
sea dutter. Any shadows will show as dark sectors in the dutter. See
Fig.16.
20