Agilent Technologies 8935 Series, Руководство пользователя

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166 Chapter 7
Periodic Adjustments
Periodic Calibration Menu Descriptions
As an alternate method, you can select the option
Timebase Reference
Using a Source
(see following section) and adjust the timebase to a
time standard connect to the front-panel ANT IN connector.
Timebase Reference Using a Source
This program automatically tunes the timebase tuning DACs to the
signal at the front-panel ANT IN connector, which is input at the
frequency that is keyed in from the front-panel keypad. If an external
10 MHz reference is being used, it must be disconnected.
In order for the calibration to be valid, the signal applied to the ANT IN
connector must have the following characteristics.
1. The level should be between
−
30 and +20 dBm (0.001 and 100 mW).
2. The frequency should be between 0.4 and 1000 MHz.
3. The frequency must be as accurate as the application of the Test Set
requires.
4. The Test Set must be able to tune to within 10 or 100 kHz of the
reference signal with the Test Set’s current timebase reference
settings. If this condition is not met, either the keyed-in frequency is
incorrect or the Test Set is faulty.
5. The signal must be a CW signal. Specifically, any FM must be less
than 100 Hz peak as measured by the Test Set.
6. The coarse tune DAC must be between 3 and 250 (decimal);
otherwise, the frequency of the source is out of reach by the tuning
DAC.
After the coarse and fine tune DAC settings have been determined, the
values are downloaded into the Test Set’s memory.
Voltmeter References
When you select the Voltmeter Reference calibration, instructions are
displayed explaining how to measure the negative and positive
references with an external voltmeter. The user is required to key in the
readings. If the readings are within range, the two values are
automatically downloaded.
For the Test Set to meet published specifications, the external DC
voltmeter must be
±
0.015% accurate when measuring
±
5 V. The
voltmeter is connected to the test points on the Measurement board,
A2A33 assembly, see
Figure 7-4 on page 167 .