Operator's guide
some channels, you should uncheck Common values before altering them.
If you are using Scream!, you can use the Control window to change the values
of the STA and LTA periods, together with the Ratio, without restarting the
digitizer. See the documentation for Scream! for more details.
Since it is not generally advisable to trigger from broadband data, the digitizer
provides a set of standard bandpass filters to apply to the data streams before
they are tested for the trigger condition. This filtering serves to maximise
sensitivity within a the frequency band of interest, and filter out noise outside
this band. You can select which bandpass filter to use from the Trigger filter
drop-down menu. The corner frequencies of the pass band of the filter are
determined by the Nyquist frequency, which is given by the sampling rate of the
triggering data. The three filter options have pass bands between 10 % and 90
%, between 20 % and 90 % and between 50% and 90% of the data’s Nyquist
frequency, respectively.
The possible filter configurations are shown in the following table:
Tap #
Rate
(samples/s)
Bandwidth 1
(Hz)
Bandwidth 2
(Hz)
Bandwidth 5
(Hz)
0
200 10 – 90
20 – 90
50 – 90
1
100 5 – 45
10 – 45
25 – 45
50 2.5 – 22.5
5 – 22.5
12.5 – 22.5
40 2 – 18
4 – 18
10 – 18
25 1.25 – 11.25
2.5 – 11.25
6.25 – 11.25
20 1 – 9
2 – 9
5 – 9
2
50 2.5 – 22.5
5 – 22.5
12.5 – 22.5
25 1.25 – 11.25
2.5 – 11.25
6.25 – 11.25
20 1 – 9
2 – 9
5 – 9
10 0.5 – 4.5
1 – 4.5
2.5 – 4.5
8 0.4 – 3.6
0.8 – 3.6
2 – 3.6
5 0.25 – 2.25
0.5 – 2.25
1.25 – 2.25
4 0.2 – 1.8
0.4 – 1.8
1 – 1.8
2 0.1 – 0.9
0.2 – 0.9
0.5 – 0.9
3
25 1.25 – 11.25
12.5 – 11.25
6.25 – 11.25
10 0.5 – 4.5
1 – 4.5
2.5 – 4.5
5 0.25 – 2.25
0.5 – 2.25
1.25 – 2.25
4 0.2 – 1.8
0.4 – 1.8
1 – 1.8
December 2005
73
