Keysight EXG and MXG X-Series Signal Generators User’s Guide
427
Troubleshooting
RF Output
Signal Loss While Working with a Mixer
To fix signal loss at the signal generator’s RF output during low–amplitude coupled operation with
a mixer, add attenuation and increase the RF output amplitude.
The figure at right shows a
configuration in which the signal
generator provides a low
amplitude signal to a mixer.
The internally leveled signal
generator RF output (and ALC
level) is
–8 dBm. The mixer is driven with
an LO of +10 dBm and has an LO–
to–RF isolation of 15 dB. The
resulting
–5 dBm LO feedthrough enters the
signal generator’s RF output
connector and arrives at the internal detector.
Depending on frequency, it is possible for most of this LO feedthrough energy to enter the detector.
Because the detector responds to its total input power regardless of frequency, this excess energy
causes the ALC to reduce the RF output. In this example, the reverse power across the detector is
actually greater than the ALC level, which can result in loss of signal at the RF output.
To avoid damaging or degrading the performance of the signal generator,
do not exceed 33 dBm (2W)
maximum
of reverse power levels at the RF
input. See also
Tips for Preventing Signal Generator Damage
on
www.keysight.com
.
Mixer
LO
ALC
Level =
−
8 dBm
RF
Level
Signal Generator
Output Control
Detector
measures
−
8 dBm
ALC level
Detector
measures
−
5 dBm
reverse
power
LO
Feedthru
=
−
5 dBm
RF
Output
=
−
8
LO Level
=
+10
dBm
IF
Effects of Reverse Power on
