25
Reducing Interference and Noise
The K3 provides several ways to cut interference,
including DSP noise reduction, manual and auto
notch, and noise blanking. Also see
Audio Effe cts
(
AF X
, pg. 35).
There are actually two noise blankers: one at the
first I.F. (KNB3 module), and the other at the 2nd
I.F. (DSP).
N
oise reduction, noise blanking, and notch
filtering should only be used when necessary. T hese
signal processing
techniques are extremely
effective, but can introduce side effects. Sometimes,
reducing the filter bandwidth is the most effective
interference-reduction strategy.
Noise Blanking
First, tap
N B
to enable I.F. and/or DSP noise
blanking.
Next, hold
L E V E L
to set the DSP level (VFO A)
and
I
.
F.
l
e
vel
(
VFO
B)
.
You’
l
l
i
ni
t
i
al
l
y
s
ee
DS P
O FF
and
I F O FF
on the VFO A and B displays.
Rotating VFO A clockwise will turn on the DSP
NB, showing
DS P t1 -1
through
DS P t3 -7
. The
first number shows the relative pulse integration
time, and the second shows the blanking level. The
higher the numbers, the more aggressive the DSP
blanking action.
Rotating VFO B clockwise will turn on the IF NB,
showing
I F NARn
,
I F M E Dn
, or
I F WI Dn
,
where
n
is
1
-
7
.
NAR
/
M E D
/
WI D
refers to narrow/
medium/wide blanking pulse widths, and
n
is the
blanking level. Higher
n
means more aggressive
blanking action. Use
NAR
width when possible to
minimize strong-signal interaction effects.
T he
NB
icon will flash slowly if the I.F.
blanker setting is too high for the present signal
conditions. If this happens, use a lower setting.
Both the DSP and IF blanking settings are saved on
a per-band basis. If
CONFIG:NB SAVE
is set to
Y E S
, the on/off status of
NB
will be also be saved
for each band.
T he
DSP noise blanke r
is in the 2
nd
I.F., where
i
t
ca
n’
t
be
ac
t
i
va
t
ed
by
s
i
gnal
s
ou
t
s
i
de
t
he
cr
ys
t
al
filter passband. It can be used with high-duty-cycle
and complex-waveform noise generated by
computers, switching power supplies, light
dimmers, etc. T he
I.F. noise blanke r
is in the 1
st
I.F., where it can use very narrow blanking widths.
It is most effective at blanking AC line noise,
lightning, and other very broadband noise. Often, a
combination of the two is the most effective.
Noise Reduction
Noise reduction reduces
random
background noise
while preserving meaningful signals. It adds a
char
ac
t
e
r
i
s
t
i
c
“hol
l
ow”
s
ou
nd to all signals.
T ap
N R
to turn on noise reduction. NR is not
applicable in DAT A and FM modes, or with AGC
turned off.
Hold
AD J
to display the NR setting; use the VFO
B knob to tailor NR for the present band conditions.
The settings are
F1 -1
through
F4 -4
.
Higher
settings can degrade weak signals.
T he first part of
the number (
Fx
) determines which NR algorithm is
used;
F1
is the least-aggressive setting. The second
part (
-y
) controls how much of the signal is routed
through noise reduction, from
1
(50%) to
4
(100%).
Notch Filtering
Notch filtering removes interfering carriers while
leaving the desired signal relatively unaffected. The
K3 provides automatic and manual notch tuning.
Auto notch
will find and remove one carrier, and in
some cases more than one. It is only available in
SSB modes, and AGC must be turned on.
Manual notch
removes one carrier at a specified
pitch, and can be used in CW and DAT A modes as
well as voice. Since manual notching sets up a fixed
(rather than adaptive) notch, it can even suppress a
keyed carrier, i.e. a CW signal.
T ap
N TC H
to turn on notch filtering (
NTCH
icon).
This turns on Auto notch if applicable. T ap a
second time if necessary to select manual notch
(adds
icon). T ap again to turn notch off.
Hold
MAN
to adjust the manual notch frequency
using VFO B. This also selects manual notch.
Summary of Contents for K3
Page 71: ...71 K3 Block Diagram ...
