Keysight Technologies 85039B IF, Руководство пользователя и сервисное руководство

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Keysight 85309B User’s and Service Guide 1-7
Getting Started
Step 6. Adjust the LO Power
Step 6. Adjust the LO Power
The procedure below is applicable to all 85309B models, and assumes the user
has basic knowledge on the antenna test system. To learn about the various
antenna test systems, refer to the
Keysight Antenna Test Selection Guide , part
number 5968-6759E. See “Printing Copies of Documentation from the Web” in
the first section of this manual.
The front panel of the 85309B has a DETECTOR VOLTAGE window, an LO
POWER ADJUST mechanism, and an LO POWER OUT OF RANGE LED. Refer to
“85309B Front Panel Features” on page 3 . The value shown in the DETECTOR
VOLTAGE window is the voltage coming from a power detector in the reference
mixer. The voltage is directly proportional to the amount of LO power arriving
at the mixer. A label on the reference mixer shows the precise voltage which
corresponds to the power at the mixer's LO input. In the procedure below, you
adjust the LO POWER ADJUST so the DETECTOR VOLTAGE display matches
the voltage on the mixer label.
Once set, the ALC loop will maintain the desired LO power level regardless of
LO frequency. Repeat the procedure below only if you change one of the mixer
modules or the LO source.
Find the detector voltage value written on the reference mixer. Record the
value in
Table 1-1
below.
Procedure
1. Set the LO source power to 6 dBm.
2. Observe the voltage displayed in the 85309B’s front panel DETECTOR
VOLTAGE window.
3. Adjust the 85309B’s LO POWER ADJUST mechanism until the voltage
displayed in the window is equal to the voltage written in Table 1-1 (also
shown on the reference mixer label). If the LO POWER OUT OF RANGE LED
is lit, there is an unleveled ALC state. To fix the problem, refer to “LO
POWER OUT OF RANGE” on page 4 . Note that due to the long LO cable
length (the RF cable between the LO source and the 85309B) you must
compensate for cable loss by increasing the LO source power.
Table 1-1 Value Indicated on the Reference Mixer
Parameter Value
mV (typically –40 to –80):
The voltage displayed in the DETECTOR VOLTAGE window varies with
frequency. This is normal. The LO POWER OUT OF RANGE LED is lit only if
the system's automatic leveling loop cannot level the voltage sufficiently.
This can happen if the LO source is disconnected, or if more power is
needed than the 85309B unit can supply for a given frequency range.