Radar Overlay; Radar Overlay And Chart Data Alignment; Showing The Radar Overlay; Stopping The Transmission Of Radar Signals - Garmin GPSMAP 8500 Black Box Owner's Manual

The range and the bearing to the target location appear in
the upper-left corner of the screen.

Radar Overlay

When you connect your chartplotter to an optional Garmin
marine radar, you can use the Radar overlay to overlay radar
information on the Navigation chart or on the Fishing chart.
The Radar overlay superimposes radar information on the
Navigation chart or the Fishing chart. Data appears on the
Radar overlay based on the most recently used radar mode
(such as Harbor, Offshore, or Sentry), and all settings
configurations applied to the Radar overlay are also applied to
the last-used radar mode. For example, if you use Harbor mode
and then you switch to the Radar overlay, the Radar overlay
would show Harbor mode radar data. If you changed the gain
setting using the Radar overlay menu, the gain setting for
Harbor mode would change automatically.

Radar Overlay and Chart Data Alignment

When using the Radar overlay, the chartplotter aligns radar data
with chart data based on the boat heading, which is based by
default on data from a magnetic heading sensor connected
using a NMEA 0183 or NMEA 2000 network. If a heading
sensor is not available, the boat heading is based on GPS
tracking data.
GPS tracking data indicates the direction in which the boat is
moving, not the direction in which the boat is pointing. If the
boat is drifting backward or sideways due to a current or wind,
the Radar overlay may not perfectly align with the chart data.
This situation should be avoided by using boat-heading data
from an electronic compass.
If the boat heading is based on data from a magnetic heading
sensor or an automatic pilot, the heading data could be
compromised due to incorrect setup, mechanical malfunction,
magnetic interference, or other factors. If the heading data is
compromised, the Radar overlay may not align perfectly with
the chart data.

Showing the Radar Overlay

The Radar overlay displays data based on the most recently
used radar mode.
From a Radar screen, select Menu > Radar Menu >
Change Radar > Radar Overlay.
The radar picture appears in orange and overlays the
Navigation chart.

Stopping the Transmission of Radar Signals

From a Radar screen, select Menu > Radar Menu > Radar
to Standby.

Optimizing the Radar Display

You can adjust the radar display settings for reduced clutter and
increased accuracy.
NOTE: You can optimize the radar display for each radar mode.
1
Select a radar range (page
2
Restore the default value of the gain setting
3
Adjust the gain setting manually

Range of Radar Signals

The range of the radar signal indicates the length of the pulsed
signal transmitted and received by the radar. As the range
increases, the radar transmits longer pulses in order to reach
distant targets. Closer targets, especially rain and waves, also
reflect the longer pulses, which can add noise to the Radar
screen. Viewing information about longer-range targets can also
decrease the amount of space available on the Radar screen
for viewing information about shorter-range targets.
14
14).
(page 14).
(page 14).

Radar Gain and Clutter

Automatically Adjusting Gain on the Radar Screen

Auto is the default value for the gain setting. The automatic gain
setting for each radar mode is optimized for that mode, and may
differ from the automatic gain setting used for another mode.
NOTE: Depending upon the radar in use, the gain setting
configured for use in one radar mode may or may not be
applied to other radar modes or to the Radar overlay.
From a Radar screen or the Radar overlay, select Menu >
Radar Menu > Gain > Auto.
The chartplotter sets the gain automatically once, based on
average conditions, the range of the radar signal, and the
selected radar mode. The chartplotter does not readjust the
gain automatically in response to changing conditions.

Manually Adjusting Gain on the Radar Screen

For optimal radar performance that accounts for actual
conditions, you can manually adjust the gain.
NOTE: Depending upon the radar in use, the gain setting
configured for use in one radar mode may or may not be
applied to other radar modes or to the Radar overlay.
1
From a Radar screen or the Radar overlay, select Menu >
Radar Menu > Gain.
2
Select Up to raise the gain, until light speckles appear across
the Radar screen.
Data on the Radar screen is refreshed every few seconds.
As a result, the effects of manually adjusting the gain may
not appear instantly. Adjust the gain slowly.
3
Select Down to lower the gain until the speckles disappear.
4
If boats, land, or other targets are within range, select Down
to lower the gain until the targets begin to blink.
5 Select Up to raise the gain until the boats, land, or other
targets appear steadily lit on the Radar screen.
6
Minimize the appearance of nearby large objects, if
necessary.
7
Minimize the appearance of side-lobe echoes, if necessary.

Minimizing Nearby Large-Object Interference

Nearby targets of significant size, such as jetty walls, can cause
a very bright image of the target to appear on the Radar screen.
This image can obscure smaller targets located near it.
NOTE: Depending upon the radar in use, the gain setting
configured for use in one radar mode may or may not be
applied to other radar modes or to the Radar overlay.
1
From a Radar screen or the Radar overlay, select Menu >
Radar Menu > Gain.
2
Select Down to lower the gain until the smaller targets are
clearly visible on the Radar screen.
Reducing the gain to eliminate nearby large-object
interference may cause smaller or distant targets to blink or
disappear from the Radar screen.

Minimizing Side-Lobe Interference on the Radar Screen

Side-lobe interference may appear to streak outward from a
target in a semi-circular pattern. Side-lobe effects can be
avoided by reducing the gain or reducing the radar range.
NOTE: Depending upon the radar in use, the gain setting
configured for use in one radar mode may or may not be
applied to other radar modes or to the Radar overlay.
1
From a Radar screen or the Radar overlay, select Menu >
Radar Menu > Gain.
2
Select Down to lower the gain until the semi-circular,
streaked pattern disappears from the Radar screen.
Reducing the gain to eliminate side-lobe interference may
cause smaller or distant targets to blink or disappear from
the Radar screen.
Radar