Page 18 - June 2015 Volume 19 Number 6

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calibration is such that switching from WX to MAP mode causes red to switch to deep blue. So, when you see a red weather echo, switch to MAP for a sweep or two. If deep blue isn’t in that echo, it’s only a shower. If you see any blue, even a little bit, it’s a thunderstorm of at least Level 4 intensity. Add a mile or two to the circumnavigation distance.
What’s the major thing to not like about this radar? It’s another standard fault with all other manufacturers’ radars since about 1975 (the only exception being the Honeywell Primus 440/660/880 series). It has various names, ranging from XXX to WATCH, and it’s an attempt to cause radars to compensate for the attenuation behind an echo. Common logic tells you that a thunderstorm tucked behind a thunderstorm, or detected through rain, will appear weaker than fact.
So, in searching for new and wonderful features, a bright young fellow came up with a scheme to correct attenuation, many years ago. When the idea was presented to a wise old engineer at RCA named George Lucche (before it became Honeywell), he demonstrated that it doesn’t work as theory says, and can even cause echoes to become miscalibrated when a terrain object is detected. Therefore, Honeywell’s Primus series radars (offshoots from RCA) have an OFF switch on their REACT; Garmin’s WATCH on the GWX 70 doesn’t. So, the GWX 70’s feature can cause echoes to be miscalibrated under certain conditions. Fortunately, that misrepresentation is to the safe side, and is only a factor on echoes inside about 35 nm.
Second possibility, if you want to determine whether it’s merely a thunderstorm or if it’s a hail- producing bugger, when you see red in WX mode, reduce the Cal control down to about 1/2 scale. If any red remains, assume it’s producing large hail and avoid it by a minimum of
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JUNE 2015