QRP Labs QDX Manual

www.arrl.org QST March 2023 41
Reviewed by Charles Powell,
NK8O/VE3ISD/5H3DX
nk8o@arrl.net
The QRP Labs QDX Digital Transceiver is a low-
power, low-cost radio for digital operations. The
reviewed unit covers  ve HF bands — 80, 60, 40, 30,
and 20 meters — and the maximum power output is
5 W, with support for digital modes only. It comes in a
kit to be built, and you can buy a fully assembled unit
for an extra $45. See Figure 1 for the kit parts packag-
ing. The printed circuit board (PCB) comes with pre-
installed surface-mount device (SMD) components
(Figures 2 and 3 show each side of the PCB). It includes
an embedded software-de ned receiver (SDR), 24-bit
48 kilo samples per second (kS/s), a USB sound card,
CAT control, and a synthesized VFO with TCXO refer-
ence. The QDX transmits a single, clean output signal,
as it is not an SSB modulator with associated unwanted
sideband and residual carrier, or intermodulation due to
ampli er non-linearity (more on this later).
The QDX is suitable for single-tone operations. It is
reported on the QDX forum that successful RTTY oper-
ation has been accomplished. It is not suitable for CW
operation using  digi or similar programs. It is my
understanding that there is no waveform shaping that
would prevent key clicks. Modes that require multiple
simultaneous tones, such as Winlink, are not possible
with the QDX. Also, the QDX is not capable of phase-
shift keying, such as PSK31. Per the product descrip-
tion,
QDX is suitable only for single tone FSK modes,
which covers the majority of digital modes in use today.
This includes everything in WSJT-X, JS8Call, some
 digi modes e.g. RTTY, Olivia and more. QDX is not
suitable for on/off keyed modes such as CW because it
does not have click-reducing RF envelope shaping; fur-
thermore, it is not suitable for phase shift keyed modes
such as PSK31 or modes involving multiple concurrent
tones such as WinLink.
Description and Kit Assembly
While it does require a computer, the unit has only four
connections on the rear panel: an antenna BNC port, a
power connection, a 3.5-millimeter PTT, and a single
Product Review
Bottom Line
The QRP Labs QDX is a low-cost digital trans-
ceiver with a clean RF output signal for the
supported digital modes. Setting it up is fast
and easy, perfect for portable and permanent
installations.
Pascal Villeneuve, VA2PV , va2pv@arrl.org
QRP Labs QDX 5-Band HF QRP
Digital Transceiver
Figure 1 — The QDX
kit with parts packaging.
USB type B port that handles both CAT control and
audio (see Figure 4). When all the necessary physical
connections are made, the unit becomes a “black box”
that requires no other user intervention.
Since Revision 3 (Rev3, now Rev4), QRP Labs added a
standard 3.5-millimeter plug for an external PTT con-
nection that can be used without modi cation between
the QDX and the QRP Labs 50 W PA. The PTT output
can also be con gured for use with any other ampli er.

QRP Labs QDX Specifications

General

Brand	QRP Labs
Model	QDX
Category	Transceiver
Language	English