# Rdev filter shapes with 11/ 17db roll off coef

#### 07mar08

### 07mar08 17 db roll off coefficients.

The coefficients for the rdev
spectrometer were updated on 07mar08 to give more roll off. Data was
taken with:

- decimate by 8 (20 MHz) bandwidth
- 16 bit output data
- shiftenable=5
- noise (a/d rms=43 counts) , and noise (43 counts) + sine waves
(31 + 35MHz) with a/d rms=150 counts.
- 32K length spectra were computed and then averaged for 13
seconds.

The plots show the
filter shape (.ps) (.pdf):
- Page 1 shows the spectra from just the noise. The top plot is a
linear scale, the bottom plot is in db. The bottom plot
shows a roll off 17db from the center to the edge of the band.
- Page 2 has a 31 MHz and 35 MHz sine wave added to the noise.
After mixing to baseband the signals end up at 1 and 5 MHz.

### 06mar08 11 db roll off filter coef.

On 06mar08 filter coefficients were installed with
an 11 db roll off (for the 20 MHz bandwidth). The setup was:

- decimate by 8, 16 bit output, output shiftenable = 7 and 5
- Dana's noise source with a -4db sine wave at 31MHz and 35 MHz.
The red noise source and the 260 Amps in the receiver room.
- 32k length spectra averaged for 13 seconds.

The plots show the 11 db roll off filter shapes (.ps) (.pdf):

- Page 1: dana's noise source with A/D rms of 43 noise counts +
sine waves of 31 and 35 MHz (which are digitally mixed to 1,5 MHz). The
A/D rms of the noise + sinewaves was 150 counts. The rms of the output
data was 1274 counts (with an output shift enable of 7). the top plot
is linear while the bottom plot has a db scale. The birdie frequencies
show up at the correct locations.

- Page 2: red noise source with 260 MHz amps in control room. The
A/D rms was 213 counts on the noise (there were no sine waves
injected). The filter roll off is about 12 db.
- Page 3: Danas noise source with noise only. The A/D rms was 43
counts. The rms of the output data was 182 counts. The filter roll off
is 11 to 12 db.
- Page 4: danas noise source with A/D rms of 43 counts. Output
shift enable was changed from 7 down to 5. The rms on the output data
is 45.8. We still have the 12 db roll off. The rms noise within +/- 3
MHz of the center of the spectra was computed after bandpass
normalizing with a 3rd order polynomial fit. The measured rms was .112
Tsys. The expected rms from the radiometer equation was: .111 Tsys.

processing:
x101/080307/rdevtest.pro,x101/080306/rdevtest.pro

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