14 System Feature Overview
April 2011 68007024085
The flat audio response of digital is different from the traditional analog audio response. The
traditional response is a linear response and the louder one speaks, then the louder the received
volume. Figure 2-7 illustrates a traditional analog response in the curves titled Professional Series
and MOTOTRBO with IMPRES RSM (AGC off, Analog). When Analog Mic AGC is disabled, then
the Analog Mic Gain (dB) is adjustable in the CPS General Settings. Therefore, MOTOTRBO in
analog mode is able to deliver the traditional analog response and is adjustable to fit into existing
systems.
Examination of Figure 2-7 indicates that digital and traditional analog responses are similar at an
input Sound Pressure Level (SPL) of 98 dB. Below this level, analog is quieter than digital. This is
important to note as a system requiring MOTOTRBO to function as a digital radio and also as an
analog radio during migration, may experience received audio level differences that are mode
dependant. This could occur when scanning both digital and analog channels and the analog
talker is located in a quiet environment such as an office. In quiet environments many users tend
to speak softly and therefore the input will fall below the equivalent response level of 98 dB SPL.
Therefore, during the migration period, the analog response may be quieter than the digital
response.
2.2 Basic System Topologies for Digital and Analog
Operations
MOTOTRBO is a conventional radio system. In its most basic form, a MOTOTRBO system is
comprised of radios that communicate to each other directly in direct mode, through a repeater in
repeater mode, or through a set of repeaters in IP Site Connect Mode. The MOTOTRBO system
can be configured to operate in analog mode, digital mode, or in both modes.
2.2.1 Repeater and Direct Mode Configurations
In direct mode, receive and transmit functions are both carried out on the same physical channel
(i.e. transmit and receive frequencies are the same).
1. When operating in Analog Direct Mode, MOTOTRBO supports one voice path (transmit
and receive) on one physical channel, and can be configured to operate in 25 kHz channel
bandwidth systems and/or 12.5 kHz channel bandwidth systems.
The option board interface meets the timing constraint of the MPT1327 standard, which is
a signaling standard for trunked private land mobile radio system. The following features
do not work with MPT1327:
• VOX
• Scan (normal and priority)
• Battery saver
2. When operating in Digital Direct Mode, MOTOTRBO uses one physical channel
configured for a 12.5 kHz channel bandwidth. On that one direct 12.5 kHz physical
channel bandwidth, a MOTOTRBO digital system can support only one voice (or data)
path at a time. Without a repeater in place to coordinate the time slot sequence among
radios, only one radio can transmit at a time in order to guarantee transmissions do not
overlap.
In repeater-based radio communications systems, a voice path requires a pair of channels: one for
transmission, the other for reception.
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