Garmin GNC 420W Pilot's Manual Addendum

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Garmin GNC 420W Pilot's Manual Addendum Manual pdf 18 page image

14Part Two: Section 2XM Weatheris “METAR” (rather than “NEXRAD”), pressthe small right (CRSR) knob to highlightthat word. Then turn the small right knob tochange “METAR” to “NEXRAD.”3. Press the small right knob again to bringdown the cursor (that is, to stop the blinkinghighlighting of “NEXRAD”) and retain theselection.NEXRAD IntensityColors are used to identify the different NEXRADecho intensities (reflectivity) measured in dBZ (deci-bels of Z). “Reflectivity” is the amount of transmittedpower returned to the radar receiver. Reflectivity(designated by the letter Z) covers a wide range ofsignals (from very weak to very strong). So, a moreconvenient number for calculations and comparison, adecibel (or logarithmic) scale (dBZ), is used. The dBZvalues increase as the strength of the signal returnedto the radar increases. There are seven gradations forrain, two gradations for mixed rain and snow, and twogradations for snow.To display the Nexrad Intensity Legend:1. While viewing the XM Weather page, press theMENU key to display the Page Menu.2. Turn the large or small knob to select “Displaylegend?”3. Press ENT to display the Nexrad IntensityLegend.4. Turn the large or small knob to scroll throughthe full table. Press CLR to return to the normalview.NEXRAD AbnormalitiesThere are possible abnormalities regarding dis-played NEXRAD images. Some, but not all, causes ofabnormal displayed information include:• Ground Clutter• Strobes and spurious radar data• Sun strobes, when the radar antenna pointsdirectly at the sun• Military aircraft deploy metallic dust which cancause alterations in radar scans• Interference from buildings or mountains,which may cause shadows• Scheduled maintenance may put a radar off-line