Wide Area Network
We have supplied several thousand receivers for a wide area one way data network. This network uses the 67 KHz subcarrier of a local F.M. station. The network is available 24 hours of the day and transmits text and data at 4800 bits per second using a proprietary bi-phase modulation developed by the network operator. This application provides a relatively inexpensive wide area network. Similar applications include paging, stock quotations, etc.
This application has a sophisticated gathering network for news and data. The information is condensed and then encoded and transmitted using the subcarrier. The signal is received, demodulated, decoded and then presented as a continuous serial stream of data on the users computer screen.
Data verification techniques are used to insure the data is continuous under interference conditions. In this very successful network, areas of interest can be selected by the user, and alarms and automatic long term storage for selected data can be used.
Local Communication Network
Dayton Industrial Corporation has recently helped several international customers establish wide area secondary communications networks using the 67 KHz subcarrier. The receivers were all mounted in vehicles and used for receiving information, music and commercials. The receivers were modified to include a microphone input and high power audio amplifier for presenting audio and driver comments to the vehicle passengers.
Similar networks could be established for school buses, public transportation, utility vehicles and others for the purpose of relaying data, event information, news and schedules.
Studio to Field Site
We supply several types of receivers for use in applications where the studio needs one way communication with news or special event personnel over a wide area, for a long time, or before other communication networks are set up and operating. These receivers are battery operated and either crystal controlled, or a frequency selectable, PLL controlled portable receiver (Model AF272).
In this application, the 67 KHz or 92 KHz subcarrier is used to provide studio originated one way communications to the field personnel.
Special Purpose Communications
Subcarriers are used to send special purpose audio information to listeners or sites that have receivers capable of demodulating the subcarrier. The most well known of these applications is the Reading Service for the Blind. A subcarrier, usually 67 KHz, is used to carry audio information to the user. The information is generated by a group of volunteers that read local newspaper articles, selected books, magazine articles, and other information of interest. These readings are then transmitted over the local F.M. station (usually a subcarrier of a Public Radio Network station, centered around 90 MHz). Dayton Industrial Corporation has a receiver designed for these applications (Model AF500 series receivers).
Networks have been formed to provide information to a specific segment of the population based on interest, ethnic, or professional information. In these instances, the receivers are usually leased to the user. The most well known of these is MUZAK, or background music, although a great portion of the MUZAK network is now satellite based. Other networks might be ethnic, such as Korean or Greek, and provide information of prime interest to that community.
Wide Area Controls
The use of subcarriers can provide control of devices over a wide area. Examples might be valves in water control or irrigation applications, power control applications, and any application requiring control over a wide area. The data rate will dictate whether a specially designed data subcarrier system is used or whether the RDS (Radio Data System) is used. The RDS operates on a standardized data format using 57 KHz subcarrier.
Future Applications
Subcarriers have the potential for future applications. They are low cost additions to a stations ability to transmit information. They are on the air as long as the main transmitter, and they are presently available. They represent a portion of the radio communications spectrum, and hence, valuable today and in the future.
The DAB (Digital Audio Broadcasting) discussions must include the use of the subcarrier portion of the F.M. broadcast band, normally thought of as the 52 to 99 KHz portion of the baseband.
High speed data channels are being considered within the DAB system as well as independently.
The Federal Highway Administration is trying to establish the ITS (Intelligent Transportation System) using subcarriers. The information would be highway speed limits, traffic delays, etc., and eventually, data of interest in specific areas as the system is tied together with satellite positioning data.
The use of SCA subcarriers is a communication method that is available to all F.M. transmitting stations. The subcarriers, 67 KHz or 92 KHz are the most common, and are modulated onto the carrier along with the regular programming audio signals at the transmitter. Special SCA receivers then separate and demodulate these SCA signals from the main channel signals and provide an audio output. The most noted uses of the SCA channels are background music, the reading services, data, and sometimes station communications.
Dayton Industrial Corporation has been designing and building F.M. subcarrier receivers for many years. All models are designed with F.E.T. front end amplifiers and dual superheterodyne receiver I.F. sections. These design efforts result in improved receiving sensitivity, selectivity, adjacent channel rejection and lowered crosstalk. The "professional" models are designed around a phase locked loop (P.L.L.) frequency control design that is easy to program by selecting several switch positions for receiving any F.M. main channel signal (88 to 108 MHz). This design offers excellent frequency stability as well as ease of operation. Other special purpose models are available that use a crystal controlled design for frequency selection. These designs are used for special SCA transmissions related to a specific station, such as ethnic radio, reading services or special events.
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Last Updated Tuesday, July 20, 2004