Specifications

From April 2008 QST © ARRL
Finally, a dual-tone filter
with its two peaks (for mark and
space tones) is the standard filter
for RTTY operation. The filter
shapes are illustrated graphically
on the display and their values
are displayed momentarily when
they are adjusted.
Notch Filtering
The purpose of notch filtering
is to remove interfering narrow-
band interference such as a car-
rier or CW signal. The K3 has
two different kinds of notch fil-
ters. The manual notch filter is
tunable from 200 to 3920 Hz. It
works in any mode. The auto-
matic notch filter will find and
attenuate a single tone and works
in any voice mode.
Noise Blanker
The K3 includes a rather
traditional 1st IF (8215 kHz)
hardware noise blanker with a wide range
of adjustments when active. It has width set-
tings — narrow, medium and wide — that
determine the width of the offending signal
to be suppressed. Another setting controls
the relative aggressiveness of suppression
in seven steps. As a noise suppressor, the
hardware noise blanker creates holes in the
waveform. This hardware noise blanker is
useful to fight broadband hash originating
from sources such as noisy ac power lines
and motor vehicle ignition systems.
A DSP noise blanker at the 15 kHz IF
also offers a choice of 21 different set-
tings. This system attacks pulse noise by
substituting signal in place of the noise
instead of creating a hole. It’s most effec-
tive against artificial electronic noise from
sources such as a nearby computer.
Noise Reduction
When the automatic gain control (AGC)
is active, a DSP noise reduction (NR) sys-
tem can be employed with 16 different
settings to attenuate the random noise that
is ever-present in the radio spectrum. The
NR system can produce dramatic changes
in the readability of signals in any location
and with any antenna system. Time spent
experimenting with just the right adjustment
for various modes and band conditions is
most worthwhile.
Just among the noise blanker and the
noise reduction systems there are 7056 ac-
tive combinations. Noise control engineer-
ing is complex, and the operator needs to
work with tradeoffs: Heftier noise control is
usually accompanied by increased audio dis-
tortion, so a compromise needs to be found
that results in better intelligibility and lower
listener fatigue. Once a sweet spot is found,
turning the NR on and off can demonstrate
a dramatic contrast.
RIT and XIT
The usual receive or transmit incre-
mental tuning (RIT/XIT) labels show up
in the display. Changes in the RIT are
shown on the VFO A display and changes
in XIT are indicated momentarily on the
VFO B display. In addition, three LEDs
on the lower-right corner of the front panel
indicate whether the adjustment is lower in
frequency, centered or higher. Another LED
near the PHONES socket lights whenever the
transmit and receive frequencies differ.
Tuning Aids
A long-standing problem with CW and
digital modes has been accurate tuning, and
the K3 has three facilities to help. One is the
SPOT button, which emits sidetone audio
at the correct pitch, allowing the operator
to tune the received signal to match the
sidetone frequency. The second facility is
the CW/data tuning (CWT) button, which
enables a visual tuning display. The incom-
ing signal can then be tuned to coincide with
the CWT pointer.
The third facility is the real winner:
With the CWT circuit enabled, the SPOT
button automatically slides the K3 to join
the frequency of the incoming signal. CW
operators will appreciate the fact that they
can continue copying while the K3 adjusts
the frequency for zero-beat. The same
auto-spot function works with PSK31, but
may require some manual tweaking for fine
frequency adjustment.
RTTY Without a Computer
Standard or reversed 45 baud
RTTY can be decoded on a scroll-
ing K3 display, and the CW
keyer can be used to transmit FSK
RTTY directly from the K3 with
no computer interface required.
Send CW, out comes RTTY. Any
of the eight CW message memo-
ries can be programmed with
RTTY messages.
There is a 5 second pause
before the RTTY transmit diddle
switches off when controlled by
the keyer, giving the operator
some ear-scratching time while
transmitting. A useful prosign IM
can be inserted at the end of trans-
mitted text to switch immediately
to receive mode. A nonprinting
double-dash (BT) prolongs the
diddle time.
Similar receive/transmit facili-
ties are planned for other digital modes such
as PSK31. With or without the optional
100 W amplifier installed, the K3 is said to
be robust enough to allow full power opera-
tion in 100% duty cycle modes.
Visual Morse Decoding
A CW decoding display can be chosen
for both transmitted and received Morse
code. This display is especially useful for
instilling in the CW operator the discipline
of leaving proper spacing between words.
Operators may chose to have the display
operate only while transmitting. This facility
can be set manually for a given code speed
or allowed to float automatically within
presets. Yes, it also allows beginning CW
contesters to read Morse code faster than
their normal skill level.
Tuning
It’s easy to change bands with repeated
presses of the BAND up or down buttons, or
you can jump to any frequency within the
K3 range via direct keypad entry. The large
VFO A knob changes receive and transmit
frequencies simultaneously unless the K3
is in SPLIT mode, in which case the VFO B
knob controls the transmit frequency. If the
RIT or XIT is not active, the RIT/XIT encoder
can be configured to act as a coarse tuner of
VFO A for a very rapid frequency change
(QSY) or for quickly “taking the pulse” of
band conditions.
Audio Equalization
Some operators care a great deal about
receive and transmit audio quality. The K3
features audio equalization adjustments on
receive and transmit. Frequency response can
Figure 4 — There’s a lot of room inside the K3/10 for
options and upgrades such as an antenna tuner,
100 W amplifier or second receiver.