Specifications

From April 2008 QST © ARRL
Table 1
Elecraft K3/10, serial number 00158
Manufacturer’s Specifications Measured in the ARRL Lab
Frequency coverage: Receive, 0.5-30, 48- Receive and transmit, as specified.
54 MHz;* transmit, 1.8-2, 3.5-4, 5.3305,
5.3465, 5.3665, 5.3715, 5.4035, 7-7.3,
10.1-10.15, 14-14.35, 18.068-18.168,
21-21.45, 24.89-24.99, 28-29.7, 50-54 MHz.
Power requirement: 11-15 V dc (13.8 nom.); Receive, 0.91 A; transmit, 3.1 A;
receive, 0.9 A (signal present); tested at 13.8 V dc. Operation confirmed
transmit, 4 A (10 W out). at 11 V.
Modes of operation: SSB, CW, AM, FM, As specified.
PSK31, FSK, AFSK.**
Receiver Receiver Dynamic Testing
CW sensitivity, 500 Hz bandwidth: –136 dBm Noise Floor (MDS), 400 Hz bandwidth:
†
(preamp on) Preamp Off On
14 MHz –130 –137 dBm
50 MHz –128 –135 dBm
Noise figure: Not specified. 14 MHz, preamp off/on: 18/11 dB.
Blocking gain compression: 140 dB typical. Gain compression, 500 Hz bandwidth:
20 kHz offset 5/2 kHz offset
Preamp off/on Preamp off
14 MHz 139/134 dB 139/139 dB
50 MHz 135/135 dB 134/132 dB
Reciprocal Mixing (500 Hz BW): Not specified. 20/5/2 kHz offset: –116/–106/–95 dBc.
Two-Tone IMD Testing Measured Measured Calculated
Band/Preamp Spacing Input level IMD level IMD DR IP3
14 MHz/Off 20 kHz –27 dBm –130 dBm 103 dB +25 dBm
–15 dBm –97 dBm +26 dBm
0 dBm –52 dBm +26 dBm
14 MHz/On 20 kHz –38 dBm –137 dBm 99 dB +12 dBm
–23 dBm –97 dBm +14 dBm
14 MHz/Off 5 kHz –28 dBm –130 dBm 102 dB +23 dBm
–15 dBm –97 dBm +26 dBm
0 dBm –52 dBm +26 dBm
14 MHz/Off 2 kHz –28 dBm –130 dBm 102 dB +23 dBm
–15 dBm –97 dBm +26 dBm
0 dBm –52 dBm +26 dBm
50 MHz/Off 20 kHz –28 dBm –128 dBm 100 dB +22 dBm
–14 dBm –97 dBm +27 dBm
I’m an enthusiastic kit builder who has
a well-deserved reputation in the Pacific
Northwest QRP Group as “Dr Klutz.” If
anybody can figure out how to flub a kit
assembly, I’m that person. It turned out
that the K3 module kit is Bruce-proof.
Well, almost.
Taking over the dining room table, I as-
sembled the bare-bones K3, serial number
158, in about 11 hours on a brand new
static-dissipating work mat. The egg carton
I used to sort the K3 hardware only had 12
compartments. Monday morning quarter-
backing tells me that I should have used an
18 compartment carton. Using 12 compart-
ments, I sorted screws by type, but not by
size. When I was very close to finishing the
kit, I was short three
1
⁄4 inch black pan-head
screws to attach three transistors for heat
sinking. I apparently had used some
1
⁄4 inch
screws where
3
⁄16 inch ones had been speci-
fied. Luckily, Elecraft had supplied extra
1
⁄4 inch zinc pan-head screws, so I could
complete the assembly. Later, Elecraft sent
replacements for the screws I “lost.”
Building this modular kit with help from
its lavishly-illustrated K3 Assembly Manual
(available as a PDF download from the
Elecraft Web site) seemed almost too easy.
The only moderately challenging stage was
fitting the front panel circuit board assembly
to the main RF board. It took me about five
minutes of fiddling before they fit neatly
together.
I would recommend building the kit to
anybody who is physically able. It gave me
an appreciation for the superb engineer-
ing that has gone into the K3, something I
wouldn’t have experienced with the factory-
assembled version. Once completed, I was
amazed how much space was left in the
box. Some of that space is reserved for the
100 W amplifier, antenna tuner and subre-
ceiver options, but even with those installed
there will still be plenty of space available
for further hardware enhancements.
Did it work? Well, not quite at first. I plan
to eventually install an FM roofing filter in
slot 1, so I put an optional 6 kHz filter in slot
2 and the standard 2.7 kHz filter in slot 3.
It turns out that the K3 defaults to expect a
filter in slot 1. After enabling the appropriate
filter parameters in the CONFIG menu, the
K3 sang happily.
The Elecraft K3 Utility is available to
update the transceiver to the latest firm-
ware versions within a few minutes. It’s
a good idea to check Elecraft’s Web site
after assembly to see if there is a newer
version available. The K3 can be connected
to a computer via a USB-to-serial cable,
available as an option from Elecraft, or by
an ordinary serial-to-serial cable, and the
software can then be instructed to search
for new K3 upgrades periodically.
The K3 Driver’s Seat
The basic features of the K3 are simple to
learn. The three-page Quick-Start Guide in
the K3 Owner’s Manual gets the ball rolling
in short order. This feature-rich radio has
much more to offer beyond simple receiving
and transmitting, however. As with operat-
ing a high-performance automobile, these
nuanced features take more time to learn.
The Basic Operations section gives a lot of
detail in 10 pages. The Advanced Operating
Features section takes up an additional seven
pages. Menu-accessed functions require
more than five densely packed pages. Since
much of the functionality of the K3 is driven
by firmware, the list of features will surely
grow and change. Consider this a snapshot
of a moving target.
Combating Noise and Interference
Perhaps the single most powerful facility
of the K3 is a wide range of interference and
noise fighting aids. A classic problem in
non-channelized Amateur Radio operation
is to dig out a weak signal with one or more
strong signals lurking nearby, and the K3
employs several tools to help with this.
Roofing Filters
The K3 provides for selectable roofing
filters at the first IF to limit the off-frequency
signals getting into the receiver — too many
strong undesired signals may overload am-
plifier and mixer stages, causing internally
generated spurious signals that reduce re-
ceiver performance. Note that the roofing
filter’s job is only to protect the rest of the
receiver, and that the operating bandwidth
filtering is performed by the DSP.
The basic K3 is equipped with a 5 pole
2.7-kHz roofing filter that can be changed
to an 8 pole 2.8-kHz unit at time of order.
Other 8 pole roofing filters are available for
6, 2.1, 1.8 and 1 kHz, as well as 400 Hz and