49 Cordless telecommunications

Part I (49.1 – 49.3.1)

49. 1 Introduction

Cordless telephone products first appeared as a low cost option for the home in North America during the late 1970's. Technically it was a radio extension telephone that operated at low power, to conserve operating time between battery charges, and frequencies of 1.7 MHz (base to handset) and 49MHz. (handset to base). The chosen technology was analogue frequency modulation which re­sulted in prices around $ 100 for a residential unit. Although range around the home was limited, typically covering an apartment or a house and gardens, the combination of low cost and freedom of use made the idea an instant success; they sold in their millions and still do.

The success was exported to Europe by way of illegal imports into the UK, France, Germany, Holland, etc. These imports infringed local telecommunications law and practice. In the UK, for example, the frequencies chosen for North American were allocated to ma­ritime and the then broadcast television service. Furthermore their transmission characteristics gave unsatisfactory speech perfor­mance when they were connected to European public telecommuni­cations networks. Nevertheless the quantity of illegal imports demonstrated that a market existed for such a product and conse­quently the European PTT's reacted by adopting appropriate stand­ards for Europe. From this beginning the present cordless market is now on the verge of making a significant breakthrough as a natural telephone terminal apparatus in both the home, office and manufac­turing environments.

49. 1. 1 Analogue technology

Two families of analogue CT have been standardised; that based on the original North American standard (h. f. /v. h. f.) and a later higher capacity European development operating in the 900 MHz band.

49. 1. 2 H. F. /V. H. F. Analogue ct

In order to compete on equal price terms with the import of illegal North American standard product, many countries chose to adopt the same standard with or without technical design changes. In Europe the UK and France followed this course, making changes to the design that avoided radio frequency allocation and transmission quality problems, but did not significantly increase the basic pro­duction cost.

One major change was to incorporate some form of dialling and incoming call security that ensured only the legitimate handset was able to open up and receive a call from its associated base station. This stopped the accidental, or sometimes deliberate, practice of long distance calls being dialled over a neighbour's cordless terminal with consequent misdirection of the call charge. The basic technical characteristics of the UK version of this analogue CT are as follows:

1 Eight analogue FM channel pairs operating around 1.7MHz and 47. 5MHz.

2 Radiated power limited to 10 mW maximum.

3 Choice of channel pair is set at manufacture but random at time and place of purchase. Line access and incoming call security by a handshake process involving at least 60000 randomly selected binary codes.

Products to this enhanced specification have been freely available the UK since 1983. In France different frequencies were adopted (21MHz and 46MHz). More recently the North American market has concentrated both directions of transmission in the region of 49MHz in order to give more transmission channels and hence more transmission capacity. The technology, however, is basically the same and retains the very attractive low production cost.