Operating Tips; Using Amplifiers In Lower Frequency Systems; Using Amplifiers In Lower Gain Systems - Motorola BLE100 Installation And Operation Manual

Section 6

Operating Tips

This section describes using amplifiers in lower frequency systems and in lower gain systems.

Using Amplifiers in Lower Frequency Systems

When using the BLE100 in 870 MHz or 750 MHz systems, you must consider the best method
for handling the reduced bandwidth and channel-loading requirement. The following
information helps you determine the best approach.
For distribution systems designed and installed as 1 GHz systems, but carrying a reduced
channel load, there are no further concerns. You can add or remove channels at your discretion.
If the system operates with ADU/QADUs, the pilot channel cannot be disturbed. Reduced
channel loading improves distortion.
For lower-frequency systems, such as 870 MHz or 750 MHz, you will need to take into account
the reduced gain from 1 GHz. Due to the amplifier tilt, there will be some loss in gain from the
published operational specification at 1 GHz. For example, a 34 dB 1 GHz BLE with 14 dB of
output tilt will lose approximately 1.3 dB of gain at 870 MHz, resulting in approximately
32.7 dB of gain at 870 MHz. If you need to adjust tilt, you may accommodate by changing the
forward equalizer (SFE) value. Also, to avoid any additional loss in gain, it is optimal to use the
equalizers that match the system frequency. For an 870 MHz system, the SFE-87-*s are the
best choice, even in a 1 GHz amplifier. Note also, that the equalizer cuts off at the frequency
value for which it is designed. For example, an SFE-87-* cuts off frequencies above 870 MHz.
Therefore, if you have a 1 GHz system and need the equalizer to perform to 1 GHz, you must
use an SFE-100-*.

Using Amplifiers in Lower Gain Systems

There are two pad facilities in the forward path: (1) the pad location (JXP-IN) at the input to the
amplifier, and (2) the midstage pad (JXP-MID) located between the pre-amplifier and the output
hybrid.
The input pad (JXP-IN) is normally changed to accommodate excessive input levels. When
operating at the same output levels, a BLE100 with an input pad has the same carrier-to-noise
(c/n) and distortion performance as a BLE100 without the input pad. Because it only attenuates
excess signal, it has no effect on the overall performance of the BLE100.
If necessary, to achieve the gain specification, you can use the midstage pad (JXP-MID) to
reduce the gain of the BLE100. However, this will affect amplifier performance. This pad
location has minimal impact on the noise figure, therefore, carrier-to-noise performance is
maintained. When operating at the same output levels, the midstage pad forces the
pre-amplifier to operate at a higher output level, thereby degrading station distortion
performance. Due to the superior distortion performance provided by the latest E-GaAs BLEs,
this should not be a major concern assuming the pad value is reasonable.
It is recommended that you contact Motorola's TRC or your account representative for specific
information regarding use of the midstage pads.
BLE100 Installation and Operation Manual