res a much better signal to noise of the crystal oscillator itself, than is needed to meet 40dB Address 1 X 4 address 2 X 4 address 30k X 2 in the lower frequency h.f. case. It should be such that noise on the capacity address line will not interfere with normal working with a 20dB signal to Tone call rate 5 call/s 15 call/s at 5.7 call/s noise ratio at the slave end of the line. Noise bursts however will 512 baud temporarily unlock the synchronisation. Message call 2.5 call/s 12 5 call/s 10 A guide to a specification is that the slave must synchronise CH; 0.45 CH; 0.52 correctly with noise bursts of maximum duration of 1 second, at an call/s 80 CH call/s 80 CH amplitude equal to the synchronising signal. Frequency of the mas- ter oscillator, may drift by up 40ppm at h.f. and 10ppm at u.h.f. Transmission 300/600 512 or 1200 200 units over worst conditions of temperature and/or time. Acquisition of lock and synchronisation of performance should be met over the Decoder type asynchronous whole of these ranges. synchronisatio Speech signals may be passed down the synchronisation line, in n and word which case a low pass filter will be used to attenuate speech framing frequencies above 2.5kHz. This leaves the range 2.8kHz to 3.0kHz Random to be available for the control signal. errors: Detection Random Wide area paging errors: Correction 45.7.1 Tone code formats Burst errors: Detection City wide paging was developed by US BELL in the early 1960's, Burst errors: followed by the Dutch PTT who opened their national Semafoon Correction network at v.h.f. using Motorola EIA 5 Tone signalling. This had an address capacity of 100,000 with a calling rate of 5 calls per second. Tone duration was 33mS and tone frequency relationship was an representation, and minimum standards for numeric and alpha arithmetic progression. The first pan-European system, Eurosignal, numeric messaging were agreed. commenced in 1967, uses 6 tone sequential system and has a Table 45.5 compares the basis parameters of three of the most capacity of ove