HP 400D Organizational, Ds, Gs, And Depot Maintenance Manual page 64

TM 11-6625-1514-15
400D/H/L Vacuum Tube Voltmeters, the
Models 403A/B AC Transistor Voltmeter, the
Model 204B Transistorized Oscillator. In ad-
dition, the Model 11004A can be used with the
405BR/CR Automatic DC Digital Voltmeter or
with the Model 457A AC-to-DC Converter (for
ac measurements to obtain digital measure-
ments).
The instrument can be connected to the out-
put terminals of a Model 200CD Wide Range
Oscillator to provide fully balanced output for
a 135-ohm or 600-ohm balanced line.
A typical setup for a 600-ohm balanced line
is shown in figure 10-3A; figure 10-3B shows
the connection for 135-ohm balanced line.
Figure 10-4 shows a typical bridging type
of measurement setup. The Model 11004A pro-
vides for voltage measurements on 135- or 600-
ohm lines without grounding one side of the
line.
Voltage measurement in dbm (0 dbm = 1
mw in 600 ohms) on a balanced 135-ohm line
may be made without grounding one side of
the line.
The Models 200CD and 400D may be used
in conjunction with the Model 11004A to form
a signal generator for measurement in the
carrier frequency range. The Model 400D Volt-
meter is connected across the output terminals
of the Model 200CD Oscillator to monitor the
output of the oscillator. The model 11004A
couples the oscillator to the balanced line. Fig-
ure 10-5 shows the signal generator setup.
10-7. Bridging Transformer Model 11005A
10-8. The Hewlett-Packard Bridging Trans-
former Model 11005A operates at audio fre-
quencies to match or bridge single ended meas-
uring instruments and signal generators to
balanced lines without disturbing the circuit
under test. The Model 11005A is shown in
figure 10-6; specifications are given in table
10-2.
The Model 11006A permits the use of single
ended VTVM's such at the H-P Models
400D/H and 400L and Distortion and Wave
Analyzers such as the H-P Models 330B/C and
10-2
330D to work from balanced lines without dis-
turbing the circuits under test. It will bridge
transmission lines at 10,000 ohms and is
equipped with a switch to allow 600-ohm line
termination.
10-9. When it is desired to terminate a bal-
anced communications system into unbalanced
measuring equipment, described under para-
graph 10-10, the Model 11005A satisfies the
dual requirements with the line terminated into
the primary with the switch in the 600-ohm
position. Figure 10-7 shows how the Model
11005A should be connected.
When measuring points with single ended in-
struments along a balanced system operating
under normal conditions, the toggle switch
should be in the 10,000-ohm bridging position.
This prevents circuit loading and at the same
time satisfies the transition from the balanced
to the single-ended condition.
10-10. The following rules should be observed
when using the Model 11005A.
a. Use 10 K position when bridging a bal-
anced system for measurements with single
ended instruments such as the H-P Model
330B/C/D Distortion Analyzers, Model 302A
Harmonic Wave Analyzer, Model 400D VTVM
or 400 H/L VTVM.
b. Use 10 K position when driving a 600 Ω
balanced system with a single ended oscillator
which has a 600-ohm output impedance such as
the 201C Audio Oscillator or an unbalanced
attenuator such as the H-P Model 200CD
Audio Oscillator.
c. Use 600 Ω position when terminating a
balanced line into single ended measuring in-
struments.
d. Use 600 Ω position with 400 Ω series re-
sistor as shown for 1000 Ω unbalanced oscillator
(fig. 10-7) .
10-11. The Model 11005A contains a 10,000-
ohm bridging resistor across the secondary
winding of the transformer. The toggle switch
parallels this bridging resistance with a 638-
ohm resistor when it is in the 600-ohm position
to present a 600-ohm match to the line.
AGO 7945A