You may have noticed that Rob Sherwood, NC0B, has added the KX3 to his
receiver performance table (http://www.sherweng.com/table.html). Rob's
test procedure is very similar to our own, so we're not surprised to
see these excellent results.
Both the K3 and KX3 are near the top of the chart. Like other
receivers in this range, they can handle crowded band conditions. But
the two rigs have completely different receiver architectures, with
The KX3 uses an architecture similar to many PC-based "SDRs" (software
defined radios), with direct conversion to base-band (AF) or to a very
low I.F. This architecture takes fewer components than a multi-
conversion superhet, facilitating a low-current, ultra-portable
implementation. That was our primary goal for the KX3. It also allows
us to provide a direct sound-card output for use with SDR programs
such as HDSDR that offer a panadapter (spectral display) and other
(The K3 is also an SDR, in that the DSP and MCU code can be quickly
and easily udpated to add new modulation/demodulation techniques, etc.
However, adding a spectral display to the K3 requires other hardware,
such as the P3 panadapter.)
In contrast, the K3 uses a classic superhet architecture: it down-
converts to a medium I.F. (in this case 8.2 MHz), where it is possible
to use very narrow crystal filters. With an appropriate narrow filter
selected, the K3 can provide extremely high dynamic range at close
spacings. Its crystal filters and 15-kHz second I.F. provide nearly
infinite opposite-sideband rejection, as well as very high blocking
If you're considering purchasing a K3 or KX3, but you're not sure
which one would be best for you, I'd offer this advice: If you plan to
do a lot of portable operation, or have limited space at home, the KX3
is ideal. If you want the absolute best possible close-in dynamic
range performance in contest or pile-up conditions (under 2 kHz
spacing), go with the K3.
The K3 also has an internal 100-W amplifier option. The KX3's 100-W
amp will be external--well suited to a mobile installation, for example.