Notch Filter (Dsp); Rf Gain Control; If Noise Blanker (Nb); Dsp Noise Reduction (Nr) - Yaesu FT-920 Operating Manual

passband may cause interference to reception by
"pumping" the AGC, causing the desired signal to fade
in and out rapidly. Engage the Narrow CW filter, if
installed, or use the S
fending signal before it reaches the DSP stage.
N Filter (DSP)
OTCH
Unwanted beat notes inside the RX filter passband
can be effectively removed by utilization of the DSP
Notch function. The DSP system will detect the beat
note, then automatically center a sharp notch filter to
eliminate the beat note. If multiple beat notes are
present the DSP will create multiple notch filters to
eliminate them!
To activate the DSP Notch Filter, press the [N
key. To turn the filter off, press the [N
more.
Note: The DSP Notch filter should not be used in the
CW mode! The DSP system will interpret a CW car-
rier as being "interference," and will notch out the in-
coming signal. Therefore, as you tune the band with
the Notch Filter on, CW signals will appear for a mo-
ment, then disappear as they are notched out.
RF G Control
AIN
The RF G control is a highly useful interference-
AIN
fighting control that is often overlooked.
When interference or background noise are severe,
rotating the RF G
AIN
in some instances, improve reception. Counter-clock-
wise rotation of the RF G
in the RF and IF stages by applying an increasing
amount of AGC voltage; this causes the background
noise and signal levels to decrease, and it also causes
the "no-signal" indication of the S-meter to rise. Sig-
nals weaker than the minimum S-meter indication
may still be plainly audible, but they will no longer be
affecting the AGC system.
This may be exploited by the skillful operator, par-
ticularly with regard to the DSP system. Because the
DSP operates in the audio section of the receiver,
after AGC detection is accomplished, rotating the RF
G control counter-clockwise may reduce the detri-
AIN
mental effects of strong noise and interfering signals,
and may render the DSP more effective at eliminat-
ing beat notes, adjacent-frequency interference, or
noise. To do this, reduce the setting of the RF G
44
control, to roll off the of-
HIFT
OTCH
] key once
OTCH
control counter-clockwise may,
control reduces the gain
AIN
control until the S-meter hangs up approximately at
the peak signal level of the interfering signal; this
places the incoming signals below the AGC Thresh-
old (described on page 42). Now engage or adjust
the necessary DSP features, and you will, in many
circumstances, find that interference rejection is im-
proved.
For maximum sensitivity, the RF G
be set fully clockwise.

IF Noise Blanker (NB)

When automotive ignition noise, power-line noise, or
other impulse-type noise is present, the IF Noise
Blanker feature may be engaged so as to minimize
] or eliminate the noise.
Press the [NB] switch so as to illuminate the NB icon
on the display, then rotate the NB L
the point of maximum noise elimination consistent
with the maintenance of good signal quality. Press
the [NB] switch again to turn off the IF Noise Blanker.
Note: Under extremely strong signal conditions on a
crowded band, such as during a DX contest, etc.,
excessive advancement of the NB L
cause somewhat degraded immunity from "splatter"
from very strong nearby stations. This general ten-
dency is typical of all IF noise blanker circuits, and
the FT-920's circuitry is carefully designed to mini-
mize this characteristic. Try reducing the setting of
the NB L control if this is observed, and try to
EVEL
utilize the DSP Noise Reduction to compensate (see
below).

DSP Noise Reduction (NR)

The DSP system of your FT-920 includes a highly-
effective Noise Reduction circuit. The DSP Noise
Reduction is particularly helpful in enhancing signal-
to-noise ratio by lowering the overall level of back-
ground noise. The DSP Noise Reduction works to
improve on the action of the IF Noise Blanker by elimi-
nating lower-level, non-impulse-type noises that are
difficult for the IF Noise Blanker to detect.
To activate the DSP Noise Reduction, rotate the NR
control clockwise from its default position, which is
fully to the left. Adjust the setting of the NR control
until the best signal-to-noise ratio is achieved. Also
try adjusting the setting of the RF G
cussion previously, to see if reducing the RF/IF gain
AIN
control should
AIN
control to
EVEL
control may
EVEL
, per the dis-
AIN
FT-920 Operating Manual