View Single Post
Old 26th Apr 2000, 10:39
  #9 (permalink)  
Join Date: Aug 1998
Location: Ex-pat Aussie in the UK
Posts: 5,215

Prof2MDA, I disagree about Archie Trammel's radar course, I bought it (with my own, tax deductable, money) and thought it was OK

Jurassic Jet Man,

The differences you are experiencing are not due to the differences in propagation of c-band and x-band radar signals, they are due to a different philosophy in radar presentation with the "newer" radars (post late 70's).

Your older C-band was designed back in the days before legal departments got involved in radar design. The radar display was calibrated to show the different reflectivity of a weather system, measured in decibels (dbz). The reflectivity is a function of precipitation density.

Beginning in the 1930s research pilots have penetrated hundreds of storm cells in instrumented aircraft, as radar scientists concurrently measured the radar reflectiveness of the cells.

This data first became available 25 years ago in a benchmark report prepared by J.T. (Jean) Lee of the US National Severe Storms Laboratory. Since that time radar displays have been calibrated to show the "red" area to indicate storms with a reflectivity above 40 dbz. Eariler radars used the contour hole to show this level of precipitation.

In the 70s, when tort law in the US began to drive everything, radar engineers were told to modify their STC (Sensentivity Timing Control) curves so that the closer a pilot gets to an area of rain the redder it gets. The STC desensitises the radar reciver to acount for the strong returns recieved from close echos, typically within about 30-40 miles (but up to 250 miles on some sets).

In short, your newer X-band has a purposely misdesigned STC arrangement, giving you a false picture at close ranges. A bad situation, but you have to fight the lawyers to change it (or keep your old radar!).
Checkboard is offline