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Working with
Mixers/Reverse
Power Effects
Note
Uncoupled operation applies to Option 001 synthesizers only.
Uncoupled operation is useful when working with mixers. Figure 1-16
shows a hypothetical setup where the synthesizer is providing
a small signal to a mixer. The synthesizer output is -8
dBm,
which in Leveling Node
Normal
results in
ATTEN
=
0
dB,
ALC Level = -8
dBm.
The mixer is driven with an LO of
+lO
dBm,
and has LO to RF isolation of 15 dB. The resulting LO feedthrough
of -5
dBm
enters the synthesizer’s OUTPUT port, goes through
the attenuator with no loss, and arrives at the internal detector.
Depending on frequency, it is possible for most of this energy to enter
the detector. Since the detector responds to its total input power
regardless of frequency, this excess energy causes the leveling circuit
to reduce its output. In this example the reverse power is actually
larger than the ALC level, which may result in the synthesizer output
being shut off.
Figure 1-17 shows the same setup, with uncoupled operation used to
produce the same -8
dBm
output. In this case,
ATTEN
= -10
dB,
ALC Level =
+2
dBm.
The ALC level is 10 dB higher, and the
attenuator reduces the LO feedthrough by 10 dB. Thus the detector
sees a
-l-2
dBm
desired signal versus a possible -15
dBm
undesired
signal. This 17 dB difference results in a maximum 0.1 shift in the
synthesizer output level. To set the synthesizer to the attenuator
uncoupled mode as discussed in this example, do the following:
.
1. Press POWER
(MENU).
2. Select Set
Atten
and press
(iJ
@J
(dB(m)).
This step does two
things, it uncouples the attenuator from the rest of the ALC
system, and it lets you set an attenuator value, in this case, 10 dB.
3. Press [POWER
LEVEL)
(?J
(j-l).
This sets the ALC level to
+2
dBm.
For more information on the ALC or setting power level, refer to
IALC)
or
(POWER
LEVEL)
in Chapter 2.
I-30
Getting Started Advanced