www.arrl.org
QST
February 2023 43
Lab Notes: Xiegu XPA125B 1.8 – 50 MHz 100 W Amplifier
The Xiegu XPA125B amplifier presented quite the challenge for the ARRL
Lab to test. We had originally obtained a slightly older version of this ampli
-
fier. It worked well enough, except for the problem that the RF power
output was low on the upper bands. This might not have been a problem in
and of itself, but when we pushed it hard to get closer to the rated power,
the transmit IMD performance was not good at all. We then found that
Xiegu had a new and improved version of the amplifier, so the editors
decided to review the new unit.
When we received the new version, we saw the same problem with power
output on the 10- and 6-meter bands. Worse, this unit did not meet the
FCC limits for spurious emissions on 6 meters. We had purchased the
amplifier through HRO, so we contacted them. HRO immediately agreed to
exchange the amplifier for us. The replacement arrived promptly. It was a
bit low on power on the upper bands, but not as bad as the older version
had been. But the unit would not go into transmit on 80 meters and dis
-
played a
LOW EFFICIENCY
error message. Again, HRO immediately
agreed to help, and we soon had a third unit. (Kudos to HRO for its excel
-
lent customer service!)
Like the previous two amplifiers, this amplifier, again, did not meet its power
output specification on both the 10- and 6-meter bands (see Table 1). The
harmonics on 6 meters did not meet the FCC limits for spurious emissions.
If this amp is to be used on 6 meters, an external filter must be used.
The transmit IMD, measured at full available power on all applicable bands,
was marginal, but a noticeable improvement was observed when the
output power was reduced to around 80 W (see Figures B and C). If users
of this amplifier want to be good neighbors on the bands, on SSB it is best
to throttle the output back from full power to achieve the cleanest signal
from the amplifier on any band.
The amplifier showed another unexpected anomaly. The input power was
reading significantly low on the amplifier’s input power meter compared to
the input power measured on the Lab’s wattmeter. For example, on 20
meters, the input power read 0.5 W, with an input power of 5 W measured
using an external wattmeter. The amplifier is specified for an input power of
5 W, so to prevent damaging the amplifier with overdrive, note the setting
of your transceiver, which produces a 5 W RF output, and be sure not to
exceed that while operating with this amplifier. We did not see this problem
on the other amplifiers we tested, so the unit that customers receive may or
may not have this problem, but it is something that customers should look
out for.
It might just be the bad luck of the draw, but the Lab found problems with
each of the amplifiers it tested. It makes a good HF CW amplifier for your
QRP rig. It can be used on FM, although it did get quite warm during test
-
ing, so it would be best to throttle it back a bit. It works on SSB, but it will
be quite a bit cleaner if it is operated at about 80% of the power it will
achieve on all bands. And on 6 meters, a low-pass or band-pass filter will
be a must to avoid exceeding the FCC limits on harmonics. —
George
Spatta, W1GKS, ARRL Assistant Laboratory Manager
Figure C
— Xiegu XPA125B 20-meter
band IMD performance at 80 W. Third-
order products are –28 dBc, and fifth-order
products are –39 dBc. Overall, throttling
back to 80 W will transmit a cleaner signal
on the bands.
Figure A
— Xiegu XPA125B amplifier input
versus output power.
Figure B
— Xiegu XPA125B amplifier
transmit IMD at 100 W on 20 meters.
Frequency (kHz)
fc
fc
−
4
fc
−
2
fc+2
fc+4
Response (dB)
–140
–130
–120
–110
–100
–90
–80
–70
–60
–50
–40
QS2302-ProdRev-B
Frequency (kHz)
fc
fc
−
4
fc
−
2
fc+2
fc+4
Response (dB)
–140
–130
–120
–110
–100
–90
–80
–70
–60
–50
–40
QS2302-ProdRev-C
0
2.0
3.0
4.0
1.0
5.0
0
20
40
60
80
100
120
Input (W)
Output (W)
QS2302-Prodrev-A
20 meters
6 meters
0
2.0
3.0
4.0
1.0
5.0
0
20
40
60
80
100
120
Input (W)
Output (W)
QS2302-Prodrev-A
20 meters
6 meters
