40 February 2023
QST
www.arrl.org
Product Review
Bottom Line
The XPA125B is a compact 100 W amplifier
that is designed to work with any QRP trans-
ceiver. The built-in automatic antenna tuner
adds to its operating flexibility. However,
there are technical issues that one needs to
be aware of.
Pascal Villeneuve, VA2PV, [email protected]
Reviewed by Phil Salas, AD5X
Besides my main station Elecraft K-Line (K3/
KPA500/KAT500), I also own some QRP rigs
— namely Elecraft KX3, Xiegu X5105, and
Xiegu G90 transceivers — which I use pri-
marily for portable operations. The Xiegu
XPA125B 100 W amplifier is an interesting
addition for those who want to use their QRP radios
as part of their higher-power fixed station. While the
XPA125B is clearly designed to seamlessly interface
with the Xiegu X108G, X5105, X6100, and G90 trans-
ceivers, it will also work with any QRP rig. And an
internal wide-range automatic antenna tuner provides
antenna system flexibility when necessary.
XPA125B Amplifier Technical Details
The XPA125B is powered directly from a standard
13.8 V dc power supply capable of 20 – 25 A. There
is no fan (i.e., the heavy metal case provides the nec-
essary thermal protection), and a handle on the left
side provides ease of transport. The amplifier is spec-
ified to output 100 W on 160 – 10 meters, and 80 W
on 6 meters, typically with less than 5 W of drive.
Transmit and receive switching is provided by an
internal relay. There is an amplifier bypass switch,
and the XPA125B is also bypassed when it is pow-
ered off. The XPA125B provides manual band
changing for non-Xiegu transceivers, and auto band
switching when used with Xiegu transceivers.
The XPA125B Display and Fault System
There is significant control, monitoring, and display
information available on the XPA125B’s LCD front
panel display. Displayed functions include input and
output SWR, input and output RF power, voltage and
current, PA stage temperature, and band and ATU
status. Four buttons provide manual control of the
amplifier: the one on the left is an
ON/OFF
power
button, the
PA
is used to switch between standby and
operating, the
BAND
button is for band selection, and
ATU/TUNE
enables the automatic antenna tuner. The
XPA125B also monitors multiple parameters to protect
it from damage. These include high SWR (>3:1), high
current (≥25 A), high voltage (≥15 V dc), and high
temperature (≥100 °C). A fault condition suspends
normal operations, normally by bypassing the ampli-
fier. Faults clear automatically when the amplifier is
unkeyed. The full XPA125B specifications are shown
in Table 1.
Setting Up the Amplifier
Begin by installing the 30 A fuse in the fuse holder if it
is not pre-installed. Connect the following: a ground
wire, the antenna coax into the SO-239
ANT
con-
Figure 1
— The Xiegu XPA125B rear panel.
