Two-tone modem A two-tone modem for use on HF radio circuits has been designed by Cossor Electronics, UK. The FSK Modem Type CGT 1090 can handle teleprinter, telegraph and data signals at speeds of 50 to 300 bit/s. Cossor claim a very good performance under marginal radio propagation conditions.

Transmission is by means of FSK tones keyed in accordance with the incoming signal. The tones are selec- ted from a range of 16 covering the frequency band (225 + 170N) Hz where N is 1-16.

These tones are allocated in pairs to particular digital signal so that one tone represents 'mark' and the other 'space' to optimize the transmission rate to the characteristics of the radio path.

Reception is by means of law asses- sor techniques, where each tone (i.e. mark or space) is individually detected and demodulated. The resulting sig- nals are combined in an optimum ratio

Portable data terminal

Access to computer information from a pocket-sized portable radio is provided by the RDX 1000 portable data terminal developed by Motorola.

The RDX is a self-contained FM transmitter/receiver designed, at the moment, to be compatible with the IBM 360/370 information display sys- tem for data entry, retrieval and update applications. The radio has been developed for indoor and outdoor use, and requires no telephone lines, inter- connecting cables or external power sou roe.

The terminal system comprises the RDX 1000 portable terminal, a duplex FM radio base station and an RDX 1100 control unit, which can handle up to 32 portable terminals.

Two-way, real-time communication between the portable terminal and the computer is by two links:

• an FM radiolink between the ter- minal and the base station,

• a synchronized landline link be-

squared combiner, thus giving inband diversity reception. Sample and hold detection is used to maintain optimum threshold during frequency selective fading.

At the heart of the demodulator is an N-path matched filter with a variable bandwidth that is matched to the incoming signal speed, the filter centre frequencies being accurate to 50 x 106. The filter thus provides programmable matched bandwidth with centre-frequency stability.

Diversity switching circuits are incorporated that provide out-of- band diversity by means of path selec- tion based on signal/noise ratio. In- puts are required from two receivers operating in space, frequency or polar diversity. Quadruple div.ersity results from combination with the tone- detection system. (Cossor Electro- nics L td, The Pinnacles, Elizabeth Way, Harlow, Essex CM19 5 BB, UK. Tel: Harlow (02 79) 26862) []

tween the RDX 1100 control unit and the computer.

The radio operates in the UHF band, sending and receiving information from the base station at 80 character/s, while the RDX 1100 control unit communicates with the IBM computer system at standard transfer rates of from 1 200 to 9 600 bit/s.

The system is expected to have a wide range of applications, including freight traffic management, stock control, materials handling and load distribution management.

An optional detachable light-pen powered by the portable terminal is available that permits bidirectional entry of bar-coded data. U sing Code 39 alphanumeric bar code, product information such as item, location, price and data can be read by the RDX. (Motorola Communications, Armstrong Road, Daneshill East, Basingstoke, Hants., UK. Tel: Basingstoke (0256) 58211, Tx: 858823) []

Miniature teleprinter

A lightweight, portable teleprinter designed to be carried in the pocket of a soldier's combat uniform or in an executive's briefcase has been develo- ped by RacaI-Datacom.

In its defence role, the micropro- cessor-controlled teleprinter comprises three small units that provide front- line troops with a hard-copy communi- cations channel that reduces the risk of human error resulting from audible commands over telephone or radio links. For the executive or travelling salesman, the three units can be com- bined with an acoustic coupler in a briefcase to provide a portable tele- printer terminal that can be used any- where there is a telephone link.

The teleprinter operates over exis- ting telephone and HF/VHF radio net- works. It provides duplex operation at 200 bit/s over telephone lines and automatically switches to simplex for radio communications. All three units, the MA 4270 alphanumeric keyboard unit, the MA 4233 miniature printer and the MA 4280 FSK telegraph mo- dem, contain internal nickel-cadmium rechargeable batteries giving approxi- mately 12 h of normal use.

The MA 4270 microprocessor-based alphnumeric keyboard unit measures 170 x 114 x 58 mm and incorporates a 35-key hermetically sealed qwerty keyboard, a single-character alphanu- meric display and six status indicators. It may be operated in conversational or store mode.

The microprocessor-based MA 4233 miniature printer measures 232 x 170 x 63 mm and accepts continuous serial data at speeds of up to 600 bit/s.

The MA 4280 FSK telegraph modem provides the means of linking the send- only terminal and the miniature printer to the telphone or radio link. It mea- sures 170 x 114 x 58 mm.

All three units of the teleprinter are sealed in cast aluminium cases; the printer mechanism is sealed by a print cover to protect against moisture and dust and it uses metallic moisture-proof paper. (RacaI-Datacorn Ltd, Milford Industrial Estate, Tollgate Road, Salis- bury, Wilts. SP1 2]G, UK. Tel: Salisbury 2391 I) []

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