Westel Wireless

Application requirement: Local basestation

General description:

An agency requires a small conventional system centered on a dispatch center.

Communication modes:

Dispatch voice communications to field personnel.
Voice communications between field personnel.
Calls from field personnel into the telephone system.
Diagnostic data to a PC or IP-based intranet.

Network configuration:

A single basestation interconnected with PABX/PSTN and intranet.

Power:

110/240 AC or 12 VDC from a battery bank.

Solution

Installation:

A single or dual radio basestation is installed in an environmentally controlled dispatch center as a desktop, rack mount or floor mount unit. Normal antenna connections are made through the TX and RX connectors on the rear of the basestation, and AC power is connected to the rear of the unit.

Basestation configuration

The basestation is configured with:

VHF or UHF Transceiver modules;

VHF or UHF power amplifiers;

AC power supply modules;

Interface module with 2-wire and/or 4-wire interfaces.

Interconnection:

Connections are made to:

PABX/PSTN via 2-wire interface for each radio; or manually patched by the dispatcher;

the data network via RS232 or Ethernet;

a dispatch console via rear panel audio for each radio.

Talkgroup configuration:

Talkgroups and frequencies are set up on subscriber units for each agency group requiring separate communication, with groups either operating in Project 25 digital or CTCSS/CDCSS analog mode, depending on the user terminals available within each group.

Basestation programming:

Each radio is programmed with Tx and Rx frequencies, Rx and Tx network access codes, modulation scheme (digital or analog) and output power for up to 512 channels.

The basestation will repeat any signal received on the selected channel's Rx frequency with the selected modulation scheme, provided the signal has the correct NAC (in digital mode) or a valid CTCSS / CDCSS signal (in analog mode).

The dispatcher can change the selected channel by use of a DTMF keypad connected to the transceiver front panel RJ11 socket (e.g. DTMF microphone).

TGID or CTCSS / CDCSS codes for each channel can also be programmed into the basestation, and these determine the addressing of any calls made on this channel by the dispatcher.

Allocation of channels to individual basestation radios will depend on the amount of traffic expected on each channel, and on the frequency plan.

Wireline interfaces are also available to each radio and configured using the programming software.

Dispatch Operation

In digital mode, the dispatcher can:

listen to all calls on a basestation radio by selecting "Monitor" mode on any channel having the required frequency pair;

listen to calls on a specific talkgroup by selecting "Selective squelch" mode on the channel corresponding to the talkgroup;

make calls on a specific talkgroup by keying the channel corresponding to the talkgroup;

make calls to all users by keying a channel set to the default "all user" talkgroup.

In analog mode, the dispatcher can:

listen to all calls with a valid CTCSS or CDCSS tone / code on a basestation radio by selecting "Monitor" mode on any channel having the required frequency pair;

make calls to a specific CTCSS or CDCSS group by keying the channel corresponding to the CTCSS or CDCSS tone / code.

Subscriber unit operation

Subscribers can:

communicate with the dispatcher on any talkgroup (providing the dispatcher is in "monitor" or "normal squelch" mode);

communicate with specific talkgroups by selecting the corresponding channel.

Variations
Battery backup A single or dual radio basestation is installed in an environmentally controlled dispatch center as a desktop, rack mount or floor mount unit. Normal antenna connections are made through the TX and RX connectors on the rear of the basestation, and AC power is connected to the rear of the unit.
Link Radio If the coverage area is remote from the dispatch center, the local basestation may be set up as a link radio to a remote repeater having a crossband link radio and working channel.
Link Radio Network If an extended coverage area is required, the local basestation may be set up with two radios; one operating as a local working channel and the second as a link to a remote repeater with a link and a remote working channel. By crossbanding the local and remote stations, a single talkgroup may be established to cover both local and remote coverage areas.
Cross band If an extended coverage area is required, the local basestation may be set up with two radios; one operating as a local working channel and the second as a link to a remote repeater with a link and a remote working channel. By crossbanding the local and remote stations, a single talkgroup may be established to cover both local and remote coverage areas. Cross band talkgroups are programmed into the basestation radios by entering the corresponding crossband channel in each channel table. The basestation then checks the Talkgroup ID or CTCSS code of all incoming calls and repeats on both radios for all talkgroups configured as crossband.