Vectronics VEC-884 - Manual (Page 64)

VEC-884 Owner's Manual
Filter Description 5-12
Overlapped Filters
When the passbands of two filters touch each other, the filters are said to be
"overlapped." The result is a single band-pass filter capable of passing all the
frequencies of the two individual filters. The filter actually changes its center
frequency and bandwidth settings so that the two individual filters are
effectively implemented as a single filter.
The new center frequency, fc, is at the center of the lowest cutoff frequency
and the highest cutoff frequency of the two individual filters:
fc = (lowest cutoff freq. + highest cutoff freq.) ÷ 2
The new bandwidth, BW, is equal to the sum of the two individual filters'
bandwidths, BW1 and BW2, minus the overlapped region:
BW = BW1 + BW2 - (overlapped region)
Overlapped filters are not noticeable by the operator. However when using the
Talk feature, an operator may notice a difference in the front panel controls
and the Tunable Filters left and right knob settings. Overlapped filters can only
occur in the following filter modes: 2BP and CW with sidetone filter enabled.
For example: The
Filters switch is set to 2BP. The Tunable Filters left and
right knobs are set at center frequencies of 2000 Hz and
2400 Hz, respectively. The bandwidth of each filter is 600 Hz.
In this case, the upper cutoff frequency of the first filter is
2300 Hz and the lower cutoff frequency of the second filter is
2100. Obviously the two filters overlap each other by 200 Hz;
therefore, the DSP implements these two filters as a single
band-pass filter. When the Talk feature is used, the DSP will
send the following:
2BP CF 2200 BW 1000