42 February 2023
QST
www.arrl.org
Table 1
Xiegu XPA125B, serial number
X02DG22210070
FCC ID number 2ANLH-XPA125B.
Manufacturer’s Specifications
Measured in the ARRL Lab
Frequency range: 1.8 – 30 and
160-, 80-, 60-, 40-, 30-, 20-, 17-, 15-, 12-,
50 – 54 MHz.
10-, 6-meter bands, as specified.*
Power output:
100 W PEP with 12 V ~ 15 V dc
100
W, as specified on 160 – 12 meters,
on 160 – 10 meters; 80 W on 6 meters.
79 W on 10 meters, 62 W on 6 meters
with 13.8 V dc.
Driving power required: Max 5 W.
1.8 – 54 MHz, 0.2 – 5.0 W (see Figure A).
Spurious and harmonic suppression:
HF, >61 dB; 6 meters, 50 – 76 dB.
>50 dB.
All bands except 6 meters meet FCC
requirements.
Third-order intermodulation distortion (IMD): 3rd/5th/7th/9th-order products
Not specified.
(dB below PEP at full output):
14 MHz, –20/–29/–41/–48 dB.
See Figure B
(dB below PEP at 80 W output):
14 MHz, –28/–39/–38/–46 dB.
See Figure C.
Transmit-receive switching time:
Key to RF output:
Not specified.
31 ms.
Unkey to receive: 30 ms.
Power requirements: 12 – 15 V dc, 30 A max.
Size (height, width, depth, excluding knobs, handles, and connectors):
2.8 × 6.3 × 10.3 inches. Weight: 5.86 pounds.
*In the US, the legal power limit on 30 meters is 200 W PEP output, and on 60 meters
it is an ERP of 100 W PEP relative to a half-wave dipole.
Table 2
Xiegu XPA125B Amplifier Measurements, 13.8 V dc
amplifier display. Standby: 0.16 A, key down, no drive, 2.1 A.
Band True Input XPA125B XPA125B True
Gain
DC Amps
Mon In
Mon Out
Output
Act/Mea
160 M
1.0 W
0.1 W
61 W
62 W
17.9 dB
10/11
2.0 W
0.3 W
86 W
89 W
16.5 dB
11.8/14
3.0 W
0.5 W
94 W
98 W
15.1 dB
12.4/14
4.0 W
0.7 W
98 W
103 W
14.1 dB
12.6/14
5.0 W
0.9 W
100 W
108 W
13.3 dB
12.7/14
20 M
1.0 W
0 W
73 W
72 W
18.6 dB
7.9/8
2.0 W
0 W
85 W
85 W
16.3 dB
8.7/9
3.0 W
0.1 W
92 W
91 W
14.8 dB
9.3/9
4.0 W
0.2 W
95 W
96 W
13.8 dB
9.7/10
5.0 W
0.3 W
100 W
100 W
13.0 dB
10/10
10 M
1.0 W
0.1 W
68 W
63 W
18.0 dB
6.9/7
2.0 W
0.1 W
86 W
82 W
16.1 dB
8/8
3.0 W
0.2 W
91 W
87 W
14.6 dB
8.5/9
4.0 W
0.3 W
93 W
89 W
13.5 dB
8.8/9
5.0 W
0.4 W
97 W
94 W
12.7 dB
9.1/9
6 M
1.0 W
0.1 W
37 W
30 W
14.8 dB
7.5/8
2.0 W
0.3 W
52 W
44 W
13.4 dB
9.3/10
3.0 W
0.7 W
63 W
51 W
12.3 dB
10.2/11
4.0 W
1.0 W
72 W
57 W
11.5 dB
11.1/12
5.0 W
1.4 W
76 W
62 W
10.9 dB
11.8/13
always shows 1:1, as it is looking
into the input of the on-line amplifier.
Finally, the gain drops as you
increase drive. This indicates that
the amplifier is going into compres-
sion at the higher power levels.
This implies that you are degrading
IMD as you near the amplifier’s
rated output. My KX3 has a built-in
two-tone generator, so I looked at
the barefoot KX3, and then the
KX3 driving the XPA125B to 94 W
on 20 meters (external power
supply set to 13.8 V). As you can
see in Figures 2 and 3, there is sig-
nificant degradation of IMD perfor-
mance when the amplifier is used.
The XPA125B Automatic
Antenna Tuner
The XPA125B internal ATU pro-
vides manual (user-initiated) tuning.
Tuning is initiated when the
ATU/
TUNE
button is pressed for several
seconds, and 5 W of RF carrier is
applied. The ATU can be used
whether the amplifier is on-line or
not. If your QRP transceiver doesn’t
include an ATU, the XPA125B will
take care of this for you. However,
as mentioned earlier, the XPA125B
SWR meters do not work unless
the amplifier is on-line and keyed.
The automatic tuner will tune, but
you have no indication of the final
SWR unless your QRP transceiver
has an SWR meter.
Tuner Matching and
Loss Measurements
Resistive matching range and loss
testing was performed with the
precision setup described in the
“Product Review” column in the
August 2012 issue of
QST
(see
www.arrl.org/qst-in-depth
for
details). Tuning power was set at
5 W, per Xiegu recommendations.
All measured losses are subject to
the ±3% accuracy of my NIST-
traceable test equipment. The
XPA125B tuning range is specified
at 14 – 500
Ω
resistive, though
