b. Recording of test data.
The readings obtained in the test are
recorded in the idle circuit noise data sheet, figure 1-2.
The allowable
noise and noise frequency weighting are taken from the DCA test parameters
specified for the circuit under test. The DCA parameter identification is
entered in DCS Circuit Type.
(1) Terminate one end of the line in an accurate resistor (600 ohms,
1%). If the line is either left open or is shorted, the impedance mismatch
that results causes noise on the line to rise to a higher value.
The
termination is accomplished by patching the sending line jack to the
resistor jack.
This automatically removes the signal from the circuit,
makes the circuit idle, and terminates the line. The meter reading at the
receiving end of the line represents only noise, since the signal has been
removed.
(2) Patch the receive end of the line to the LINE jack of the TTS-37B
with the INPUT control set to TERM 600, and select the weighting specified
by the parameter designated by the TSO. Weighting switch positions include
C MSG, HIGH PASS, 3KC and 15KC. When C MSG weighting is selected, the noise
reading will be dBrnc.
(3) Read the noise level on the DBRN scale of the meter by adjusting
the SENS controls. Enter the readings on the form (figure 1-2).
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