Section III
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
Model 3555B 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
