Anritsu RA773UA, Инструкция по эксплуатации

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D. Distant false echoes caused by duct phenomenon
Depending on meteorological conditions, duct phenomenon sometimes occurs in temperature
inverting layers of air. In such a case, the wave propagates erratically reaching a location surprisingly far
away from the ship. In this case, a target present at a distant location more than the radar's maximum
distance range appears on the screen presenting a false echo that can be misunderstood to be present nearer
than the actual position. This phenomenon is attributed to the fact that since echo from the distant target
arrives late, it gets out of the pulse repetition frequency and is displayed on the screen as an echo in the
next frequency. If the target distance changes as you switch over the distance range, you can determine that
it is a false echo.
Radar interference
If a radar operating in the same frequency exists near your ship,
interference noise may appear on the screen that is caused by
transmitted waves from that radar. This interference appears in various
ways. In most cases, however, it appears as spiral or radial patterns.
The RA773/774UA radar has a function to eliminate interference.
Use of this function helps you minimize interference.
2.3 Terms Specific to Radar
HM (Heading Marker)
This is a line-shaped marker used to indicate the
advancing direction of your ship.
North Mark
This marker indicates the north direction. It is a short line approximately 1/6 of the screen size.
Display modes
This refers to a radar's display modes. There are four display modes depending on the direction in which the
top of the screen faces with respect to the ship.
Fig.2-8 Radar interference
Fig.2-9 Heading Marker and
North Mark