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Section III Model 3555B
Figure 3-8. Simple Test for Inductive and Capacitive Coupling
0dBC = 0.775V across any impedance as read on an
-hp- Model 400D AC Vacuum Tube Voltmeter. Thus,
the dBC is strictly a relative term.
3-66. Measurements can easily be made in dBC. by
utilizing the Model 3555B Telephone Test Meter. To
make these measurements, set FUNCTION to 600 and
the INPUT switch to TMS BRDG. Any termination
required other than 600 ohms must be provided
externally and connected across the two binding posts T
and R. Termination can also be made using a patch
cord and any one of the other INPUT jacks since all
INPUT jacks are connected in parallel. If a 600 ohm
termination is to be used, the internal termination can be
utilized by placing the INPUT switch to the TMS TERM
position.
3-67. MEASUREMENT PROCEDURES.
3-68. Tables 3-3 through 3-8 list the step by step
procedures for measuring levels and noise balance,
recorder calibration and transmission loss using the
3555B. For a more detailed discussion on level and
noise measurements refer to paragraphs 3-12 through
3-47.
3-69. 150 BAL CONVERSION.
3-70. The 3555B comes equipped with all the
necessary parts for converting the 135 BAL function to a
150 BAL function. The following is a simplified
procedure for making the modification.
a. Remove the set from the case and remove
the FUNCTION board. Clip the shorting
wire from across A1R17 (see Figure 7-2)
and reinstall the FUNCTION board. Leave
the set out of the case.
b. Set the 3555B controls as follows:
RANGE..........................................0dBm
FUNCTION................................135 BAL
INPUT ..................................TMS TERM
c. Remove the 150 BAL decal from the
envelope supplied with the set. Remove
the backing from the decal and place it
over the 135 BAL function pushbutton.
d. Connect a 150 ohm balanced source to the
input of the 3555B at a level of 0dBm
(387mV rms) at a frequency of 1kHz. Turn
the 3555B ON and adjust A3R24 (Figure 7-
3) for 0dBm indication on the 3555B meter.
e. Reinstall the set in its case.
3-12