Motorola MOTOTRBO SYSTEM PLANNER Specifications download pdf (Page 211)

202 System Design Considerations

November, 2008

• If group data is to be supported on a system, the inclusion of preambles should be added to

minimize the occurrence of the group data message being missed while an SU is on the

GPS Revert Channel.

• Avoid situations where a large number of subscribers are powered on in a relatively short

period of time as this causes a flood of registration messages that impacts the voice quality

of service on the Selected Channel during the registration process. See “GPS Revert and

Loading” on page 152. for recommendations on minimizing impact when using Motorola

applications.

• In order to minimize users from inadvertently changing a radio to the GPS Revert Channel, it

is recommended that the GPS Revert Channel(s) is placed in a different zone than the

primary voice and data channel(s).

4.11 Failure Preparedness

4.11.1 Direct Mode Fallback (Talkaround)

A repeater channel is defined by having different receive and transmit frequencies, and any

channel that is programmed with the CPS to have different receive and transmit frequencies will

be considered to be a repeater channel and the MOTOTRBO radio will expect a repeater

operating on that channel. The radio user will get an access-denied tone if there is no repeater

available or if the radio is out of range of the repeater. Channels defined as repeater channels in

CPS can be modified to operate in Talkaround mode via user selection from the menu or a

programmable button. When a repeater channel is thus modified to operate in talkaround mode,

the transmit frequency is set equal to the receive frequency, and it effectively becomes a direct

mode channel. The system now performs similarly to the direct mode topologies we've previously

described.

4.11.2 Uninterrupted Power Supplies (Battery Backup)

To determine the UPS capacity you will need, follow these simple steps:

1. List all equipment to be protected by the UPS on a worksheet.

2. Read the nameplate data on each of the devices listed. Write down the voltage and

amperage for each device.

3. Multiply the voltage by the amperage of each device to calculate the Volt/Amps (VA).

Some equipment, such as PC power supplies, may be marked with a power consumption

measured in Watts. To convert Watts to VA, simply divide Watts by 0.65 (for a power fac-

tor of 0.65), or multiply by 1.54. The power factor refers to the relationship between the

apparent power (volt-amps) required by the device and the actual power (watts) produced

by the device.

4. Total the VA for all devices you want to protect with the UPS and enter it in the "Subtotal"

field.

5. Multiply the subtotal found in Step 4 by 0.25 and enter it as the "Growth Factor". This num-

ber takes into account room for future growth. This growth factor allows for a 5% rate of

growth for each year over a five-year period.

6. Add the "Growth Factor" to the Subtotal" to get the "Required VA". Now you can select the

appropriate UPS model by choosing a model that has a VA rating at least as large as the

"Required VA" that you calculated.

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Motorola MOTOTRBO SYSTEM PLANNER Specifications Page 211

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