Operating Tips; Using Amplifiers In Lower Frequency Systems; Using Amplifiers In Lower Gain Systems - Motorola STARLINE SERIES 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 MB*/* in 750 MHz or 550 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 870 MHz 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 ADUs, the pilot channel cannot be disturbed. Reduced channel
loading improves distortion.
For lower-frequency systems, such as 750 MHz or 550 MHz, to maintain amplifier gain it is
optimal to use the amplifier and equalizers that match the system frequency. For example,
750 MHz equalizers used in 550 MHz systems, result in reduced amplifier gain. Note also, that
the equalizer cuts off at the frequency value for which it is designed. For example, an SFE-75-*
cuts off frequencies above 750 MHz. Therefore, if you have an 870 MHz system and need the
equalizer to perform to 870 MHz, you should use an SFE-87-*. In the MB*/* the SFE, as well as
the MDR, are designed and optimized to a specific passband. When possible, in addition to using
the equalizers that correspond to your system frequency, also install the amplifiers designed for
that frequency. For example, in a 750 MHz system, a 750 MHz amplifier is preferred but not
required.

Using Amplifiers in Lower Gain Systems

There are three pad facilities in the forward path: (1) is the pad location (JXP-IN) at the input to
the amplifier, (2) is the midstage pad (JXP) located between the pre-amplifier and the interstage
hybrid, and (3) are the output pads (JXP 2 and JXP 3/4) located between the interstage hybrid
and the output hybrids.
The input pad (JXP-IN) is normally changed to accommodate excessive input levels. When
operating at the same output levels, an MB*/* with an input pad has the same carrier-to-noise
(c/n) and distortion performance as an MB*/* without the input pad. Because it only attenuates
excess signal, it has no effect on the overall performance of the MB*/*.
If necessary, to achieve the gain specification, you can use the midstage pad (JXP) or output
pads (JXP2 and JXP 3/4) to reduce the gain of the MB*/*. However, this will affect amplifier
performance. Output padding degrades the station distortion performance while having
minimal effect on the carrier-to-noise performance. Midstage padding is the opposite and
therefore has little effect on distortions, but degrades the carrier-to-noise performance. In
general, we recommend you pad to the gain specification on the output. However, if you are
unsure about the optimal padding technique for your system, we recommend you split the
required padding evenly between the midstage and output pad(s).
It is recommended that you contact Motorola's TRC or your account representative for more
specific information regarding use of the midstage and output pads.
MB*/* Installation and Operation Manual