contour control operation
the contour filtering system provides a gentle perturbation of the if filter passband. the contour is set to either suppress,
or boost specific frequency components, and thus enhance the sound and readability of a received signal.
interference rejection
1. press the [cont] button to activate the contour filter.
the led inside the [cont] button glows orange
and the current “null” (or “peak”) position of the contour
filter will appear in the contour indicator on
the display. the [select] knob will now function as
the contour knob.
2. rotate the [select] knob to achieve the most naturalsounding
audio reproduction on the incoming signal.
advice:
the frequency display will show the contour frequency
for 3 seconds whenever the [select] knob is turned.
3. press the [clear] button to move the “null” (or
“peak”) position to center.
4. to cancel contour tuning, press the [select] button
momentarily. the graphic disappears from the
contour indicator on the display, confirming that
the contour filter is no longer in operation.
advice:
press the [select] knob (momentarily) once more,
the contour filter is activated again.
advice:
􀂈 the contour filter selection will be memorized independently
on each vfo stack of vfo-a and vfo-b.
􀂈 the contour filter level (either a null or a peak) may
be adjusted using menu item “069 rgen cntr lv”.
the factory default setting is for a null of –15 (db).
􀂈 the bandwidth over which the contour filter effect is
applied may be adjusted using menu item “070 rgen
cntr wi”. the factory default setting is 10.
􀂈 when the optional dmu-2000 data management unit
is connected, the audio scope (on the “oscilloscope”
page) is particularly useful when adjusting the contour
control. not only can you see the effect of the
null/peak of the contour system, but you also can see
the position of the null/peak with respect to frequency
components of interest on the incoming signal. you
may then observe (on the audio scope) the effect of
the contour control while listening to the effect on the
signal, and this will help build your intuition on how
best to use contour tuning in the future.
refer to figure “b”, this illustrates an “indentation”
of the contour filter in the center of the passband.
the contour filter is placing a low-q “notch”
(per the setting of menu item “069 rgen cntr
lv”, referenced above) in the passband. counterclockwise
rotation (to the left) of the [select]
knob causes the notch to move towered a lower
frequency within the passband, while clockwise rotation
(to the right) causes the notch to move toward
a higher frequency within the passband. by
removing interference or unwanted frequency components
of the incoming signal, it is possible to
make the desired signal rise out of the background
noise/interference, enhancing intelligibility.
quick point:
the steep slopes of the dsp filtering, when adjusted aggressively, can impart an unnatural sound to an incoming signal.
often, a narrow bandwidth is not the key to improving copy; the incoming signal itself may have undesirable or excessive
frequency components, especially in the low frequency range around 100-400 hz. by judicious use of the contour filter, the
“shoulder” of the passband response may be altered, or components may be removed from within the passband, allowing the
desired signal to rise above the background noise and interference in a manner not obtainable with other filtering systems.
