Motorola V186 - Cell Phone - GSM System Planner Manual page 127

In the U.S. the FCC's rules for Fixed Secondary Signaling and for Telemetry operations
require data not to interfere with voice operations—the data message must wait until the
voice message is finished. This is a practical matter also—if a data message were
attempted simultaneously with any co-channel message, there is a high probability that
the data would be corrupted and throughput would be zero. So why create the
interference for no gain. Therefore the data equipment must listen to all on-channel
activity; PL/DPL protection on the receiver is unwanted.
PL/DPL may be used in ACE3600 or MOSCAD systems when it operates through some
existing voice repeater system that requires PL or DPL for repeater access, but the
PL/DPL is added to the transmitter and not the receiver. Note that PL/DPL should never
be used on VHF splinter channels: the FCC limits the occupied channel bandwidth by
severely limiting deviation; PL or DPL would consume too much of the authorized
deviation to produce an effective system. Never use PL/DPL with DFM modulation.
FCC Reframing (USA only)
In the U.S., the FCC has revised the rules that govern the frequencies between 150.8 and
512 MHz; the rules for the frequencies above 806 MHz have not changed. Two issues
addressed by the new rules are channel bandwidth and data efficiency on those channels.
The VHF and UHF channel bandwidth have been split. The former 25 kHz channels have
been split into two 12.5 kHz channels and will be split further into four 6.25 kHz
channels in the future. Manufacturers are required to design all new products to comply
with the new channel bandwidth requirements, but there are no requirements that force
licensees to migrate to 12.5 kHz channel operation. The MT-2000 and MCS-2000 radios
used within MOSCAD may operate on either 25 kHz or 12.5 kHz bandwidth channels;
Radio Service Software is used to define the mode of operation.
Radios used for data must meet a minimum efficiency requirement. In a separate action,
the FCC clarified key definitions.
Data is any signal that bypasses the microphone input's filters (i.e., the splatter
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filter).
Voice is any signal that passes through the microphone input's filter.
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The FSK and DPSK modulating signals are indeed data superimposed onto tone carriers
and these signals always pass through the radio's splatter filter. Therefore, these
modulating signals are voice, require an emission designator with the F3E characteristic,
and are not required to satisfy a data efficiency requirement.
VHF Splinter Channels (USA only)
In the U.S. the FCC has defined certain frequencies in the 154 MHz and 173 MHz bands
for data operation—the splinters. The frequencies are few in number, some have a 12.5
kHz bandwidth, all have a FCC-imposed deviation restriction, and are very commonly
used. In an attempt to insure that the transmitted emission stays within the assigned
channel bandwidth, the FCC has stipulated that an F2 emission must be used and that the
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Communications