Vectronics VEC-884 - Manual (Page 63)

VEC-884 Owner's Manual
Filter Description 5-11
Limited Filters
Filter response is limited to the frequency range of 0-3900 Hz or 175 Hz
minimum in SSB mode. When a filter's center frequency setting is low or high
enough that the bandwidth would exceed these frequency ranges, the filter is
"limited." The filter actually changes its center frequency and bandwidth
settings so that it does not exceed these frequency ranges.
Limited filters are probably not even noticed by the casual 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. Limited
filters can only occur in the following filter modes: LR/HR, BP, 2BP, CW, and
SSB.
For example: The
Filters switch is set to BP. The Tunable Filters left knob is
set at a 300 Hz center frequency and the Tunable Filters right
knob is set to a bandwidth of 2000 Hz. Obviously the lower
cutoff frequency cannot be -700 Hz. Since the DSP's
frequency range stops at zero, the filter must stop at zero.
The filter's upper cutoff frequency is 1000 Hz above the center
frequency, 1300 Hz. In this case, the DSP limits the BP filter
to 0-1300 Hz (a low-pass filter). Therefore when the Talk
feature is used, the DSP will send the following:
BP CF 650 BW 1300