Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.naic.edu/~phil/hardware/pdev/configGuide.html
Äàòà èçìåíåíèÿ: Sat Feb 3 01:26:08 2007
Äàòà èíäåêñèðîâàíèÿ: Sat Dec 22 11:23:51 2007
Êîäèðîâêà:
Ïîèñêîâûå ñëîâà: http www.astronomy.ru forum index.php topic 4644.0.html

Pdev configuration guide

02feb07

This page holds current measurements for the voltage/power level settings for the pdev spectrometer. The settings path is:

function	V/P	Shift Bits	Bits	Sat	notes
A/D sample	V		12	Adc Ovf
PolyFilter/ffts	V		18		19 bits arithemetic.
Pshift	V	Down	18	fft Ovf	13 bits mask. Each bitdown shifts after a butter fly stage. B0 last butterfly(size2). B12 first butter fly stage.
Shift Vshift	V	3Up	32	Vsh Sat	After fft before stokes upshift values.
Compute pwr	P		32
Dshift	P	4Dwn	32		down shift prior to accumulation.
Accumulation	P		40	Acc Sat	accumulate in 40 bit numbers. Assume 32 bit input placed in lower 32 bits of accumulator
Ashift	P	3Up	32	Ash Sat	uppper most 32 bits of accumulator are up shifted in 32 bit word. This is needed for packing 8 or 16 bits.

The input A/D should have an rms that is probably 5 counts or more to be above the digitization noise. You should allow a few extra bits so you can setup the power levels at high za and then continue observing at low za (where Tsys is lower).
The output spectrum should have enough counts so that the noise in a channel covers a few counts. This is determined by the radiometer equation: dT/T=1./Sqrt(bw*time). If T is the number of counts in the spectral channel then Dt=SpectralChanVal/sqrt(bw*time).

For a 1 second integration, 8K channels, and 170 Mhz :
1./sqrt(bw*time)=.0069.
1/.0069= 144.
So you will need a spectral channel value of 144 to have 1 count on the noise.
5 counts would be about 720.
This holds for the edges of the spectrum where the filter shape is falling off.

Testing the different setting for PFB saturation/underflow.

**minimum Pfb shift for no pfbOverFlow vs a/d levels ( if2noise source)**
A/D Lvls	Pshift	pfbOvr L,H	VSh	Dsh	Ash	Spc Med	Notes
11,10	0x1800 0x1a00	0,3 0,0	0	0	0		need >=3 shifts
26,22	0x1300 0x0013 0x1600	0,0 12,7 0,0	0	0	0		need >=3 shifts
47,40	0x1600 0x1700	7,8 0,0	0	0	0		need >=4 shifts

<- page up
home_~phil