If Notch Filter - Yaesu FT-1000MP Operating Manual

Operation
When QRM is present on both sides of the
tuned station, first adjust the SHIFT control just to
the point where the interference from one side is
eliminated, and then rotate the WIDTH control in
the opposite direction to eliminate interference
from the other side. The optimum settings of these
controls depend on the relative signal strengths of
the desired station and the QRM, and requires
practice.
SHIFT/WIDTH Tuning Steps
Rotating the SHIFT or WIDTH control tunes the
IF passband using default 10-Hz steps. If
desired, you can change to 20-Hz steps,
which offers a faster response when turning
the control knob. See menu selection -2 to set
the default steps as desired.
Notch Filter
After tuning in a desired signal and adjusting
the IF bandwidth and shift, if heterodyne interfer-
ence such as from a carrier or CW signal occurs,
activate the IF notch filter by pressing the NOTCH
button and s/owly adjusting the inner control with
the same name to null the heterodyne. Note that
if the interfering carrier is more than about +1.2
kHz away from the center of the passband, the
notch filter may be unable to null it. In this case,
switch the notch filter off, and readjust the IF
bandwidth and shift so that the undesired carrier
is outside of the passband.
<— Notch —>
Desired Desired
Signal Signal
QRM
(Heterodyne)
BANDPASS BANDPASS
i | i>
NOTCH —2— NB NOTCH -2— NB
wl @
NOTCH Action
page 34
Advice on QRM Reduction
Use the BANDWIDTH buttons and then the
SHIFT and WIDTH controls to suppress the
interference. Their use varies somewhat from
mode to mode. In general, however, you will
want to press the LOCK button beneath the
tuning knob before adjusting the SHIFT and
WIDTH controls, as accidentally retuning
would invalidate your settings (particularly in
narrow-bandwidth modes).
When you are ready to retune to a new
frequency, press LOCK again to release it, and
return the SHIFT and WIDTH controls to their
default positions (center detent). The WIDTH
control can also be turned counter-clockwise
to reduce the IF bandwidth more gradually,
and then the SHIFT control can be turned left
or right from center to shift the center
frequency lower or higher, as depicted in the
drawing.
For digital modes, the wider bandwidth
selections are fine for tuning around, but the
500 or 250 (Hz) bandwidths will generally give
the best copy with narrow shifts. If you have
the RTTY and PKT menu selections set to
match your TNC/terminal unit (see page 55),
you should not need to adjust the SHIFT
control at all, and the WIDTH control should
only be adjusted with a great deal of care (to
avoid losing the contact). See the section on
digital modes later in this manual for more
details.
For 300-baud packet, use 500 (Hz) bandwidth
and keep the WIDTH control centered; the
SHIFT control may require fine tuning either
side of center for optimum copy of weak
signals. Experiment with the SHIFT setting on
a busy packet channel, and then note the
optimum setting for all future HF packet
operation (it will be the same unless you
replace your TNC or recalibrate the input
tones).
Note - except during extreme QRM
conditions, the WIDTH and SHIFT controls
should be left in their center (detent) positions
when tuning the receiver to a new frequency.
This will provide the best fidelity and easiest
tuning.