HP 70908A, Руководство по обслуживанию

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External Frequency Reference
Most module verication tests and adjustment setups for the HP 70908A RF section require
an external frequency reference . When running these tests , the HP 70900A/B local oscillator
source module and instruments such as sources and analyzers must be connected to the same
frequency standard.
In all cases , the specied aging rate requirement is 10
09
/day . The microwave source ,
synthesized source , and calibrated spectrum analyzer each have an internal time base that
meets the aging rate requirement.
Figure 6-1 shows the preferred method of connecting a test system to a 10 MHz standard.
In (a), a frequency counter is connected to a house standard to ensure absolute frequency
accuracy .
In (b), the 10 MHz internal frequency reference of an HP 8663A synthesized signal generator
is used as the system reference . This method minimizes phase noise associated with chaining
the same reference signal through several devices; it ensures that the last instruments in
the chain receive reference signals of sucient amplitude . The HP 8721A directional bridge
splits the reference signal and ensures good isolation between the two reference signal paths .
Note
The rear panel 10 MHz OUTPUT of the HP 3335A synthesizer/level generator
lacks the spectral purity required for most applications as a frequency
reference , and should not be connected to other test equipment.
The HP 8902A measuring receiver does not have a standard rear panel 10 MHz
OUTPUT .
100 MHz Generation
The local oscillator requires a 100 MHz external reference . Most other instruments that need a
reference require 10 MHz.
There are three equipment congurations used to generate the 100 MHz signal for the local
oscillator:
HP 70310A Precision Frequency Reference and 10 MHz House Standard
In Figure 6-2 the 10 MHz frequency standard derives from the house standard (for example ,
the HP 5061B cesium beam standard). The house standard drives the HP 70310A precision
frequency reference , which then generates the 10 MHz and 100 MHz signals .
HP 70310A Precision Frequency Reference
In Figure 6-3 the reference oscillator of the HP 70310A precision frequency reference
provides a 100 MHz frequency standard output for the HP 70900A/B local oscillator source
and a 10 MHz reference for most other electronic test equipment.
HP 8566B Spectrum Analyzer and 10 MHz House Standard
In Figure 6-4 the 100 MHz signal required by the HP 70900A/B local oscillator source comes
from the HP 8566B spectrum analyzer 100 MHz calibrator output. The 6 or 10 dB pad
prevents RF amplier saturation. The RF amplier must have a gain of at least 20 dB at 100
MHz.
6-2 System Calibration