Page 16 - June 2015 Volume 19 Number 6

21st Century Radar
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Garmin now has a truly modern airborne radar. Back in 2006, the company introduced its GWX 68, which was, in several respects, far ahead of its time. However, it was designed on the chassis of a much-older radar, which had actually started life as a King Radio product. The new GWX 70 is a clean-sheet design by Garmin’s radar engineering staff, under the direction of Joel Andrews.
The major item making it a 21st -Century radar is that it’s engineered around a solid-state pulse generator. Solid-state is a 70-year leap forward, compared to the traditional coaxial or strapped vane magnetron pulse generators of most other radars. Why is this solid-state device so great? First and foremost, frequency stability. The old magnetrons, conceived by the British before WWII, spewed out a garbage of frequencies. Consequently, radar receiver gates had to be wide to hear that mess, then to work hard to pick out their own pulses from all the static – their own voice, as it were. Not so with the solid-state device. It can easily hear itself and ignore all the other chatter and static in cyberspace. As a result, transmitted pulses can be sent out with greatly-reduced power. Instead of the common 5,000 to 10,000 watts of the old days, a mere
14 • TWIN & TURBINE
40 watts will do with the GWX 70. Ithastoworkalotlesstodoitsjob.
Since it can hear better, the result is a crisper-appearing echo. Not much, but it’s there and the boundaries of each color are more exact. Plus, for your pocket book, solid-state is far more reliable than the heavy old magnetrons, meaning fewer shop visits and expense.
In truth, solid-state pulse generators are not that new; they’ve been around for 50 years in military radars and Collins introduced them in airline-category radars 30 years ago. But, the GWX 70 is the first to employ the device in radars for singles, light twins and smaller jets.
Is there no downside to it? Yes. For a low-wattage solid-state device to send a usable pulse out beyond 90 or so miles, transmission times per pulse must be much greater. To overcome that, Garmin’s engineers used “pulse compression” on the GWX 70, an engineering trick for making a pulse of radar energy act like it’s shorter than it is. Again, it’s ancient high-tech engineering, used in military radars for years, but this is a first for low-end civil radars. On the GWX 70, when a long range is selected for viewing, pulse compression shrinks the echoes down to just a mile in “range smear.” Were it not for pulse compression,
echoes would be smeared out to six miles, front to back, making it almost impossible to differentiate weather echoes from terrain when a long display range is selected. Another plus for the advanced engineering that Garmin’s engineers applied to the GWX 70.
Beyond that, the GWX 70 has the usual me-too “features” that have been added to civil airborne radars, by first one then another radar manufacturer, over the past 30 years; integrated R/T/A section from Bendix in the late 1970’s, “WATCH”, an adaptation from Collins’ ancient “PAC” and Honeywell’s “REACT”, and “Doppler Turbulence Detection,” another oldie that Garmin is promoting as though it’s totally new and unique, although it was first introduced by Collins far back in the last century. Most all experienced pilots consider Turb Detection interesting, but useless.
Garmin has even expanded “Doppler” to create a “Ground Clutter Suppression” feature, which has been around, but not really working as claimed, since the Collins WXR 850 of 1985. (Just why terrain features must be suppressed is a mystery anyway; pilots who can’t tell the difference between weather echoes and ground detail, and use that detail for enhanced safety, haven’t got enough gray
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JUNE 2015