Vertex Standard FT-1000MP manual Width Control, Width Action Using Width control to reduce QRM

OPERATION

DEALING WITH INTERFERENCE

WIDTH CONTROL

We just saw that specific IF filters can be selected to limit the receive bandpass to a pre-set width (essen- tially the total width of the installed filter). In a crowded band, you ideally want to narrow the bandwidth just to the point where the unwanted signal is attenuated while still retaining enough bandpass to recover the desired station. In real-life band conditions, however, this ideal bandwidth is often somewhere “in-between” the sev- eral selectable filter bandwidths.

The WIDTH control can be used in all modes except FM to continuously narrow or broaden the bandpass skirt (within the limit of the selected filter) for the best skirt shaping and optimum cutoff and interference rejection during

each QRM situation. Unlike older types of width con- trols that adjust both sides of the filter slope at the same time, the MARK-VFT-1000MP’s WIDTH control nar- rows the passband from either the upper or lower side (see illustration below). Thus, you only narrow the side of the bandpass where the QRM is located.

The center detent on the outer WIDTH control pro- vides maximum bandwidth, which is equal to the se- lectivity of the filter used with the operating mode. Clock-

wise rotation moves the upper skirt of the IF passband lower in frequency, and counter-clockwise rotation moves the lower skirt upwards. If a QRM condition occurs after tuning in a station, slowly rotate the con- trol in the direction where the interference is reduced while the station is still workable. As you rotate the con- trol you will hear the audio response change as the passband is narrowed. If the QRM is very close, the amount of bandwidth reduction necessary to cut the QRM may leave the desired station’s audio unrecov- erable, or it may not be possible to entirely eliminate the QRM.

When the QRM is all above or all below the desired signal it is usually only necessary to rotate the WIDTH control either to the left or right to cut the interference from the receiver passband. The SHIFT control (cov- ered next) will also work for this, but may introduce interference from the other side of the signal.

When you have activated the IDBT feature by press- ing the [IDBT] button on the Shuttle Jog, the EDSP (Contour) filter’s passband width reduces according to the WITDH knob setting. That is, the IF bandwidth and the EDSP bandwidth will be matched, according to the setting of the WIDTH control knob’s position.

WIDTH Action Using WIDTH control to reduce QRM

MARK-V FT-1000MP Operating Manual page 47