H. f. /v. h. f. analogue CT

Date: 2015-10-07; view: 400.

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.

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.