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Working with
Spectrum
Analyzers/Reverse
Power Effects
Reverse power is a problem with spectrum analyzers that do not
have preselection capability. Some analyzers have as much as
+5
dBm
LO feedthrough coming out of their RF input, at some
frequencies. The effects of reverse power are less in the heterodyne
band (0.01 to 2.3 GHz)
w
h
ere the power amplifier provides some
broadband matching. Similarly, at frequencies above 2.3 GHz, reverse
power that is within 10 MHz of the synthesizer’s frequency may be
partially absorbed by the YIG filter. If the frequency difference is
small enough to be within the leveling system bandwidth (typically
10 kHz CW, 200 kHz sweep or AM), the effect of reverse power is
amplitude modulation of the synthesizer’s output. The AM rate
equals the difference in RF frequencies. Reverse power problems may
be treated by using the unleveled mode. There are two unleveled
modes, ALC off and search.
To set the synthesizer to the ALC off mode:
1. Refer to menu map 1.
2. Press
(ALC).
3.
Select Leveling Mode
ALCoff
.
In this mode, the synthesizer provides RF power with no ALC
correction and therefore requires a power meter to set a particular
power.
To set the synthesizer to the search mode:
1. Press
(ALC.
2.
Select Leveling Mode Search.
In this mode, the synthesizer is in the normal ALC mode until the
desired power level is reached, then the ALC is disconnected.
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