PSHIFT values that work with the FAA radar.

Radar signals grow linearly in the butterfly stages (noise grows as the sqrt(number of butterflys). This can cause overflows in the butterfly stages of the fft. The values of pshift that work for the faa radar were found by:

sit at az=340 za=18 . This is where the faa radar is strong.
The A/D rms in counts was set and then data was taken for about 24 seconds and any overflows were noted.
Shorter fft's will have fewer stages in the butterflys so the overflow problem should be less severe.

PSHIFT values and Overflow status for fftlen=8192
A/D counts counts	PSHIFT 0x1ffa	PSHIFT 0x1ff5	PSHIFT 0x1fea	PSHIFT 0x1faa
20	ok	ok	pfbofl3	pfbofl8
30	ok	ok	ok	pfbofl8
40	ok	ok	ok	pfbofl8
50	ok	ok	ok	pfbofl8

Note: This data was taken in jan07 before the a/d levels of pdev were switched from 1.5 to .75 volts. After the switch the radar has a larger a/d value.. so the above pshifts need to be remeasured.

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