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142 Chapter 4
Making Measurements
Timebase Frequency
Timebase Frequency
Purpose
In the absence of a frequency counter, the measurement quickly
determines the frequency difference between the instrument’s 10 MHz
reference oscillator signal and an accurate, external 10 MHz frequency
standard.
NOTE The timebase frequency check is not as accurate as a measurement of
the
10 MHz Out signal (rear panel) using a frequency counter
referenced to a frequency standard.
Measurement Method
The internal 10 MHz reference signal is compared with a reliable
external 10 MHz signal which the user inputs into the front panel RF
connector. The transmitter tester subtracts its 10 MHz reference from
the input signal and displays the frequency difference.
Test Setup
An accurate external 10 MHz frequency signal, such as a house
standard, is connected to an attenuator, which attenuates the signal to
0 dB. The attenuated 10 MHz signal is connected to the RF input of the
transmitter tester. Pressing
Mode, Service, Measure, Timebase
Frequency will result in the display of data described below.
NOTE When setting up this test ensure that the reference is set to internal. To
check this press
System, Reference. The Freq Ref softkey allows you to
toggle between
Int (internal) and Ext (external). Make sure Int is
underlined.