Multiple radio sets

Multiple radio sets

Dispatch-reliant services, such as tow cars or ambulances, may have several radios in each vehicle. For example, tow cars may have one radio for towing company communications and a second for emergency road service communications. Ambulances may have a similar arrangement with one radio for government emergency medical services dispatch and one for company dispatch.

[edit] Multiple controls, microphones

A mobile radio in a US ambulance often has two sets of controls: one in the patient area and another near the driver.

US ambulances often have radios with dual controls and dual microphones allowing the radio to be used from the patient care area in the rear or from the vehicle's cab.^[2]

[edit] Data radio

Both tow cars and ambulances may have an additional radio which transmits and receives to support a mobile data terminal. A data terminal radio allows data communications to take place over the separate radio. In the same way that a facsimile machine has a separate phone line, this means data and voice communication can take place simultaneously over a separate radio. Early Federal Express (FedEx) radio systems used a single radio for data and voice. The radio had a request-to-speak button which, when acknowledged, allowed voice communication to the dispatch center.

Each radio works over a single band of frequencies. If a tow car company had a frequency on the same band as its auto club, a single radio with scanning might be employed for both systems. Since a mobile radio typically works on a single frequency band, multiple radios may be required in cases where communications take place over systems on more than one frequency band.^[3]

[edit] Walkie talkie converters in place of mobile radios

Intended as a cost savings, some systems employ vehicular chargers instead of a mobile radio. Each radio user is issued a walkie talkie. Each vehicle is equipped with a charger system console. The walkie talkie inserted into a vehicular charger or converter while the user is in the vehicle. The charger or converter 1) connects the walkie talkie to the vehicle's two-way radio antenna, 2) connects an amplified speaker, 3) connects a mobile microphone, and 4) charges the walkie talkie's battery. ^[4]The weak point of these systems has been connector technology which has been proven unreliable in some installations. Receiver performance is a problem in congested radio signal and urban areas. These installations are sometimes referred to as jerk-and-run systems.

[edit] Notes

1. ^ Cited in many references including on escutcheons and silk-screened face plates on 1960s Motorola products including early HT-200 and Dispatcher-series mobiles. Later HT-200s dropped the term. It was also seen on some Kaar Engineering mobile products. One example is the title on a Special Products service manual Model T31BAT-3100B-SP3 'Dispatcher' Radiophone 25-54 MC 12 W RF Power 12VDC, State of California Radio Communications System, (Chicago: Motorola Communications Division, 1965). The Oxford English Dictionary conflicts with some uses, saying radiophone is interchangeable with radiotelephone. The 11th edition of Newton's Telecom Dictionary says radiophone is an, "obsolete term."
2. ^ "Evaluating Regional Alternatives," Planning Emergency Medical Communications: Volume 2, Regional-level Planning Guide, (Washington, DC: Department of Transportation, National Highway Traffic Safety Administration, 1995) pp. 45-49.
3. ^ Paragraph 2.4(e), Arizona Phase II Final Report: Statewide Radio Interoperability Needs Assessment, Macro Corporation and The State of Arizona, 2004, pp. 15. and "Evaluating Regional Alternatives," Planning Emergency Medical Communications: Volume 2, Regional-level Planning Guide, (Washington, DC: Department of Transportation, National Highway Traffic Safety Administration, 1995) pp. 45-49.
4. ^ For example, Motorola has trademarked the name Converta-Com for a system which accomplishes all three of these tasks. Some Converta-Com systems allow the attachment of signaling devices or external devices not usually compatible with walkie talkies. One historic example is the NLN-4470A for MT-500 series radios.