HP TM 11-6625-2779-14&P manual Detailed Circuit Description, Simplified Dial BAT Function

HOLD: When the HOLD pushbutton is depressed a high inductance coil LI is connected across the Model 3555B balanced INPUT terminals if the INPUT

Section IV

4-13. The output of the Input Amplifier goes to the INPUT switch where noise filters are set up for selection by the NOISE WTG switch. In the NOISE position, either 3kHz FLAT weighting, C Message weighting, 15kHz FLAT weighting or PROGRAM weighting can be selected by the NOISE WTG switch. In the TMS position of the INPUT switch the filters are bypassed for transmission level measurements.

4-14. The output from the INPUT switch goes to the meter amplifier. This amplifier provides an ac signal to the DIAL/AC MON jacks so that a handset can be used to listen to the signal being measured. This is particularly useful in determining noise characters.

4-15. The detector circuit provides an equivalent rms detected voltage to drive the meter. The meter has shaped pole pieces to provide a linear meter scale both for dBm and dBrn.

4-16. DETAILED CIRCUIT DESCRIPTION.

4-17. The purpose of the function switch is to set up the input conditions to match the type of measurement being made. Impedances can be selected to match the lines to be tested and can be either bridged or terminated. Separate transformers are selected for voice frequency and carrier frequency measurements. A 40dB attenuator is bridged across the input terminals for longitudinal noise measurements when the Ng pushbutton is depressed. The HOLD function places a high inductance holding coil across the input terminals to simulate an off-hook condition. Each of these functions is described in detail in the following paragraphs.

a.

Model 3555B

switch is in the TERM position. A bridging HOLD is not possible. The TERM switch connects the two windings of L1 in series.

b.DIAL BAT: (See Figure 4-2)The DIAL BA1 pushbutton serves two purposes. First it disconnects the meter from the detector and connects it to the unregulated power supply so that the battery voltage can be monitored. Secondly, the DIAL/AC MON jacks are disconnected from the amplifier ac output and connected to the INPUT

jacks. This permits connecting the lineman's handset to the balanced line for the purpose of dialing.

c.Ng: (See Figure 4-3)The Ng pushbutton connects a 40dB attenuator across the balanced input terminals for longitudinal measurements. This attenuator consists of A1R5 thru A1R8 and A1C1. The output is taken from the junction of AIC1 and A1R8. This output is referenced to ground and applied to the voice frequency transformer A1T2.

d.900 (Vf/Nm): The 900 function switch S4 selects terminating resistors AIRI and A1R9 for 900 ohm terminations. The INPUT switch must be in _ the TERM position to complete the circuit for this termination. The 900 function switch also places a ground on the 900 ohm relay A3K1 which provides gain switching in the Input Amplifier so that the meter will indicate in dBm. The 900 ohm signal is applied to the voice frequency transformer A1T2. HOLD can be accomplished on this function.

Figure 4-2. Simplified DIAL BAT Function

4-2