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Your Radar’sBy Archie Trammell Gain control? What nonsense;it doesn’t “GAIN” anything.For a pilot, its most useful function is to reduce. Actually, what the control does is vary thresholds for the echo colors on your radar display. That, in turn, changes the “Calibration” of the radar display, causing it to indicate that echoes are worse than, or not as bad as, they actually are. So, fact is, it’s a “Calibration” control.they simply change thresholds for the three or four colors.The first thing you must do to use the control with intelligence is discover where the detent, or “Calibration” position, is. As a rule, for general aviation radars, that position is with the knob turned fully clockwise, but there are numerous exceptions to the rule. In their zealto make “our” radar better than “their” radar, manufacturers have given many names to the detent or “Calibrated” position, although the color values are all the same on everyone’s radar. On some radars it’s called “PRE SET”, on others “MAX”, and on still others “AUTO”. On some, there is no indication of where it is, other than the control position. If the CAL position on your radar isa mystery to you, refer to the manufacturers’ POH, ask your avionics technician or e-mail me; archie@ radar4pilots.com.(An increasing number of radars are controlled through an MFD, in which case the CAL control will be shared with some other knob. Refer to your MFD POG.)Your second task in using the control will be to discover when it’s functional and when it’s not. Many are non- functional in a WX mode and are usable only in MAP; that’s especially true of Bendix GA systems. Finally, if your radar’s CAL works only in MAP mode, check to see if the display colors change between the WX and MAP modes. Honeywell GA radars do, for example. If they change on your radar display, you’ll have to visualize the correlation between WX and MAP colors. (You should do that on any radar, so itMin GAIN MaxMin GAIN Max MinMax MinMaxIts proper label is “CAL”.Not until recently have radar manufacturers begun to call it what it actually is. is.” – Radar sets designed a generation ago have a control labeled “GAIN”, while a more recently-designed system will have a “CAL” control. What caused them to finally switch over to a name that actually describes the control’s function? They changed the way echoes are caused to be shown as the correct colors. Once upon a time, radar engineers actually varied the radar receiver’s “GAIN” to make it happen; today, with digital techniques,12 • TWIN & TURBINEMAY 2014CALCAL GAIN“Ga