pdf 6436KB Sep 25 2010 04

NCJ Review: The Elecraft K3
Revisited
A year ago, NCJ presented a contester’s
perspective on a pre-production version of
the new Elecraft K3 (“NCJ Reviews: The
Elecraft K3 — First Impressions,” Sep/Oct
2007 NCJ). The review radio was great, but
it lacked some important features in terms of
both hardware and fi rmware. This article updates
those fi rst impressions, commenting
on production version differences, added
components and features, the assembly
and support experience and published lab
tests. It also editorializes a bit on software
defi ned and modular radio experiences that
might be of importance to contesters.
Production Release
Subsequent to the fi eld test review, Elecraft
released many additional items, fi rst
to the testers and then, after ironing out
the wrinkles, to general availability. When
the first K3 production run shipped in
October 2007, the radio included a 100W
power amplifi er, hardware noise blanker
and a higher-precision TCXO. Rigs were
available either factory-assembled or as a
no-solder semi-kit. Later, Elecraft released
a full-function sub-receiver, additional fi lters
and many fi rmware upgrades. The last
included FM, ESSB, auto notch, selectivity
presets, diversity receive and continuous
improvement of nearly everything. Delivery
delays have declined to about three
months, and Elecraft continues to work on
production processes in order to reduce
the backlog.
Elecraft zealots report deliveries on the
company refl ector (elecraft@mailman.
qth.net) and track them via an independent
Wiki, www.zerobeat.net/mediawiki/
index.php. The Wiki includes product
descriptions and resource material. By
unoffi cial count, Elecraft had shipped more
than 1800 K3s through September 2008.
Hardware Additions and Corrections
Very few updates were needed to bring
fi eld test units up to production standards. I
made most of the modifi cations in the fi eld,
and today I can barely distinguish between
my fi eld test unit (serial no 12, June 2007)
and the full-production radio I built in April
2008 (serial no 744).
The most significant feature absent
from my fi eld test radio was the 100 W
power amplifi er. The K3’s PA is considerably
lighter than the one in the K2, and
it’s very easy to install. The heat sink is
entirely inside the K3 case, cooled by two
large, rear-mounted fans. These variablespeed
fans are temperature controlled and
6 November/December 2008 NCJ
quieter than those in my laptop. I literally
never hear them.
The K3 PA has very level power output,
thanks to a strong ALC algorithm that
evolved nicely during fi eld testing. Power
foldback in response to high reflected
power is gradual and effective. Below an
SWR of 2.5:1, I can get 100 to 120 W output
on 160 through 6 meters. An informal
check at 3.5:1 showed 50 W out. If you
reduce the target power below 13 W, the
100 W PA shuts down altogether, and you
have a very effi cient QRP rig.
Sub-Receiver
The most important addition in the
wake of the K3’s initial release is the
KRX3 sub-receiver. Initially, Elecraft was
not satisfi ed with signal isolation between
the main rig and the prototype KRX3.
The manufacturer delayed shipment for
several months while it designed a full
wraparound steel enclosure, tested it and
got it into production. The delay was well
worth it. The sub-receiver is, as advertised,
every bit as good as the main receiver. In
fact, its additional shielding may make it
slightly more immune to external noise
and unwanted signals than the alreadyoutstanding
primary receiver.
The sub-receiver has its own DSP, synthe-
Rick Tavan, N6XI
Elecraft with permission
Figure 1 — The KRX3 sub-receiver open; the KPA3 power amplifi er is at top center.
sizer, noise blanker and sockets for up to fi ve
crystal roofi ng fi lters. Although some owners
have equipped the KRX3 with a full fi lter
complement, matching the main receiver, I
haven’t found that necessary. So far, I am
just using the included 2.7 kHz fi ve-pole fi lter.
Since ultimate selectivity is DSP-derived,
this is acceptable except in the presence of
very strong, nearby signals.
The 2.7 kHz fi lter is essentially indistinguishable
from the 2.8 kHz eight-pole fi lter
in my main receiver except when attempting
diversity reception. Because of different
delays through those fi lters, there is a funny
phase shift that’s quite audible in the headphones
when the two receivers are tuned
to the exact same frequency. This latency
disappears when listening to different frequencies,
as in a DX pileup, my primary use
for the sub-receiver. Phase shift is not an
issue when the two receivers are equipped
with matching fi lters. I intend to reconfi gure
my fi lters so that the two receivers have
some in common — probably 2.7 and 1.0
kHz. Although it’s not diffi cult to add and
exchange fi lters, the KRX3 does introduce
additional disassembly to this process.
The K3 is no longer a svelte eight
pounder. The heavily shielded KRX3 has
pushed a fully-loaded K3 up to almost ten
pounds. Some people like that, since the