(b) Tune the oscillator to approximately 2,700 Hz. This frequency
is selected for the test because it is near the upper end of the voiceband.
Adjust the AMPLITUDE control of the oscillator until the voltmeter indicates
0.776 volts (V1). This value of voltage is equivalent to a level of 0 dBm
in 600 ohms.
(c) Measure the voltage (V2) across resistor R.
across R indicates the magnitude of unbalance of the wires in the pair to
ground. As the unbalance becomes greater, the voltage across R increases;
if the balance were perfect (a condition seldom achieved), the voltage would
be approximately zero.
This gives a high decibel figure by calculation.
The higher this figure, the better is the balance.