Elecraft K3 Owner's Manual - Manual (Page 25)

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 Effects
(
A F 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. These
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. level (VFO B). You’ll initially see DSP
OFF and IF OFF on the VFO A and B displays.
Rotating VFO A clockwise will turn on the DSP
NB, showing
DSP t1-1 through DSP 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
IF NARn , IF MEDn , or IF WIDn ,
where n is 1 - 7 . NAR / MED / WID 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.
The 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
YES , the on/off status of N B will be also be saved
for each band.
The DSP noise blanker is in the 2 nd I.F., where
it can’t be activated by signals outside the crystal
filter passband. It can be used with high-duty-cycle
and complex-waveform noise generated by
computers, switching power supplies, light
dimmers, etc. The I.F. noise blanker 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
characteristic “hollow” sound to all signals.
N R turns noise reduction on. It doesn’t apply to
DATA or FM modes, or with AGC turned off.
Hold A D J to display the NR setting, which is
saved per-mode. Use the VFO B knob to tailor NR
for the present band conditions. In general, the
higher the number, the more aggressive the noise
reduction. Settings
F1- 1 through F4- 4 are
recommended. F5- 1 through F8- 4 use a different
algorithm, where the -x part of the setting indicates
the degree of mix between the DSP-processed and
unprocessed signals (
-1 is about 50% processed, -4
is 100%). A small
M
appears to remind you that a
M ixed setting is in effect, e.g. NR M F5 -1 .
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. (SSB mode only.)
Manual notch removes one carrier at a specified
pitch, and can be used in CW and DATA 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 Morse code signal.
Tap N T C H to turn on notch filtering ( NTC H icon).
This turns on Auto notch in SSB mode, and
Manual notch in other modes (adds
icon).
Holding M A N U A L directly selects manual notch in
any mode. Adjust the manual notch frequency using
VFO B, then tap
N T C H again to exit.