HP TM 11-6625-2779-14&P - Manual (Page 18)

Section III Model 3555B
frequency Transmission Measuring Set (TMS) for voice,
program and carrier multiplex measurements. The set will
operate over a wide range of environmental conditions and
maintain a high degree of accuracy.
3-16.
In general, transmission level measurements are
made by connecting the circuit under test to the INPUT
jacks with a suitable patch cord, selecting the proper
bridging or terminate condition and impedance, and then
operating the RANGE switch to provide an on-scale meter
indication. Transmission level measurements are made
with the INPUT switch in TMS position either bridging or
terminated. In this position, the set has its maximum
frequency range.
3-17.
The multiple INPUT jacks and binding posts
accept the Western Electric 309, 310 and 358 single plugs
and the 241 or 289 twin plug. The two red binding posts
marked T (tip) and R (ring) will accept banana plugs,
spade lugs, phone tips or bare wires. These jacks and
binding posts are all connected in parallel and only one
should be used at a time. A patching cord such as the
Western Electric 3P12H, consisting of a cord with a 310
plug on one end and a 309 plug on the other end, should
be kept with the instrument as a universal patch cord. The
75 ohm jack accepts Western Electric type 358 plugs for
75 ohms. unbalanced carrier measurements.
3-18.
The sleeves of all the INPUT and DIAL jacks are
connected together and to the black binding post marked
S. The binding post in turn, is connected through a swing-
away shorting strap to a second black binding post marked
G. This binding post is the measuring set case ground.
When it is necessary to establish a battery or ground
connection on the sleeve for PBX test purposes, this
shorting strap may be disconnected by loosening the black
binding posts and swinging away the strap. A cord is then
connected to the S terminal and may be connected to the
battery or ground for the test. Type 347 plugs must not be
used when the shorting strap is removed.
3-19.
The multiple jacks marked DIAL/AC MON are
connected in parallel and accept a 310 or a 347 single plug
or a 289 dual plug. A dial with the impulse springs
connected to the tip and ring of a 310 or 347 plug may be
used or a lineman's handset such as the Western Electric
1011 B may be connected to the two square clip posts for
the dialing and talk operation. When the FUNCTION
pushbutton marked DIAL/BAT is depressed, the DIAL
jacks are connected to the INPUT jacks and a number may
be dialed on the line connected to the INPUT jacks. The
circuit is arranged for loop dial operation and the circuit
under test must supply talk battery.
3-20.
Once the switching equipment has been seized by
the dialing operation, the connection can be held by
depressing the HOLD pushbutton. This places a dc bridge
consisting of a high impedance retardation coil, across the
INPUT terminals. This coil has negligible effect on
measurements of voice frequencies. Once any other
pushbutton is depressed, the AC output of the internal
amplifier circuit is returned to the DIAL/AC MON jacks for
an external head Model 3555B phone which can be used
to monitor the noise or tones being measured. The
lineman's hand set which was used for the dialing
operation can be used for monitering by leaving it
connected to the clip posts. The jacks marked 310 will
accept a head phone or recorder connected to the tip and
ring of a 310 plug or tip and sleeve of a 347 plug. The
performance of the set is not affected by this output and
any impedance head-phone may be used.
3-21.
The DIAL/BAT function also checks the power
source used. The green arc on the meter marked BAT
GOOD corresponding to the green BAT marking on the
pushbutton, indicates the range of voltages for proper
operation. Full scale corresponds to 60 volts and the left
end of the arc corresponds to the battery cut-off voltage of
24 volts. Thus the remaining battery life can be estimated
by noting the position of the pointer in the green arc.
Since the set POWER must be turned ON to perform this
check, the battery is properly loaded to give a true
indication of its condition. When operating from the
external office battery or AC power, the meter monitors
this voltage to indicate if it is the correct level to properly
power the set. The POWER switch turns OFF and ON all
power to the set.
3-22.
The remaining FUNCTIONS are used to set up the
input conditions. The Ng function will be discussed under
the paragraph heading, "NOISE MEASUREMENTS". The
impedance of the set is selected by the pushbuttons
marked 900 and 600 for voice frequencies and 600, 135
and 75 for carrier frequencies. The 900 and 600 ohm
impedances are normally used for loop plant testing while
600, 135 and 75 ohms are usually reserved for carrier
system measurements. A bridged or terminated condition
is determined by the position of the INPUT switch. Using
this procedure, the meter will always indicate in dBm for
the impedance selected, bridging or terminated. The
terminations, when used, are provided with a dc blocking
capacitor. Accidental application of carrier or telegraph
battery, office battery or ringing voltage will not damage
the set. The pushbutton marked HOLD bypasses the
INPUT switch and terminates the circuit in addition to
placing the holding bridge across the line that is connected
to the INPUT. When the INPUT switch is in either of the
NOISE positions, weighting filters can be selected by the
NOISE WTG switch for noise measurements.
3-23.
The RANGE switch selects the dBm range of the
meter. To avoid overloading the set, turn the RANGE
switch to +30dBm when connecting a circuit for testing.
Once the circuit connection is established turn the RANGE
switch counterclockwise until an on-scale indication is
obtained. The black dBm marking on the RANGE switch
identifies the input level required to deflect the meter to
the 0 mark on the black scale. The meter uses shaped
pole pieces to present linear dBm markings on the scale
with marks at 0.1 dBm increments. The accuracy and
resolution of this type of meter is the same at any point on
the scale and it is not necessary to keep the pointer in the
upper portion of the scale for maximum accuracy. The
accuracy of the set is not affected by the position of the
set. This type of meter will have the pointer off-scale to
the left
3-6