Motorola BT100 Amplifier Level Control, Manual Gain Control, Temperature, Gain Reserve

Amplifier Setup 3-9

attenuation changes due to temperature. If necessary, you can control the Bode board manually using the potentiometer labeled manual level (MAN) in Figure 2-13.

Amplifier Level Control

Signal levels vary in a cable system primarily because cable attenuation changes with temperature. Other components such as passives and amplifier hybrids are also affected by temperature changes. To automatically compensate for these signal level fluctuations and control output level, you must select the optional ADU, QADU, or TDU. The use of the ADU, QADU, or TDU is recommended for improved output level stability.

When necessary and appropriate, you can also use manual gain control. The gain of the BT100 is then determined by the potentiometer marked MAN on the electronics chassis cover.

Manual Gain Control

To use manual gain control:

1Verify that the electronics chassis is installed correctly.

2Ensure that there is continuity in the forward path by installing the design-value forward equalizer and design value input JXP-*B attenuator.

3Ensure that the drive control select jumper is in the MAN position.

4Use a signal-level meter to measure the high band-edge carrier input level at the input test point: 750 MHz = channel 116, 870 MHz = channel 136, 1003 MHz = channel 158.

This carrier should be at standard analog level, non-scrambled.

5Verify that the input level agrees with the design specification input.

If the level is different from design, adjust accordingly. For example: the design level is 19 dBmV at the highest frequency and the design pad value is JXP-3B. If the actual measured level is 21 dBmV, then you must change the pad to a JXP-5B.

If the actual levels are significantly different from the design levels, it is recommended that you investigate or consult system management before proceeding.

6Connect the signal-level meter to the output test point and tune the meter to the high-end channel.

7Turn the manual gain reserve (MAN) control (illustrated in Figure 2-13) to maximum (fully clockwise) and then reduce the output as noted in Table 3-3 below:

Table 3-3

Gain reserve versus ambient temperature

Temperature			Gain Reserve
°	°		3 dB
Above 110 F (43 C)			4 dB
° °	°	°
32 F (0 C) to 110 F (43 C)
°	°		5 dB
Below 32 F (0 C)

8Check the amplifier output tilt by measuring the high band- and low band-edge carriers.

ƒHigh = channel 116 (745.25 MHz), channel 136 (865.25 MHz), or channel 158 (997.25 MHz).

BT100 Installation and Operation Manual