FINAL REPORT - Stakeholders - Ofcom

6.12.5 Possible Improvements to Existing Technology
The use of 25 kHz equipment with a maximum deviation of 16 kHz is not compatible with
12.5 kHz equipment working on the four interleaved channels. In order to minimise
possible interference, use of 12.5 kHz technology on all ten channels is encouraged. This
will not eliminate interference altogether, because there may be on-board
communications by ships under foreign flags with 25 kHz technology in the same harbour
area as new equipment, but it will significantly reduce the probability of interference.
Consider e.g. the Cowes yachting regatta with a great need for on-board
communications. Simultaneous use of 25 kHz and 12.5 kHz equipment will create
interference both ways; into the 25 kHz receiver from the interleaved 12.5 kHz channel
and into the 12.5 kHz receiver from the 25 kHz transmitter with a maximum deviation of
16 kHz spilling over into the interleaved 12.5 kHz channel.
6.12.6 Possible New Technologies (in-band)
In the medium to long run, implementation of digital techniques is possible and desirable.
There may also be a need for data communications in addition to voice. Some of the
channels indicated in Section 6.12.1 could be identified for digital on-board
communications. ITU-R should be invited to study the matter.
6.12.7 Possible Overall Spectrum Efficiency Improvements
The use of 12.5 kHz channels and the implementation of digital techniques will improve
spectrum efficiency. However in the case of interleaving FM channels there is an issue of
reduced deviation and therefore reduced coverage. Studies conducted in the UK in the
late 1960s concerning the implementation of a VHF radiotelephone service concluded
that in theory a 12.5 kHz mobile receiver would require between 6.2 and 13 dB more
signal than a 25 kHz mobile for a comparative edge of service performance in an urban
environment. However low power systems such as on board systems generally have a
reduced dynamic range of signals and this is favourable to the narrower channel spacing
condition. Against this there is a small deterioration in signal to noise ratios at 12.5 kHz
spacing due to the reduced deviation. This occurs chiefly in the good signal areas and
amounts to 2.5 – 3 dB. This is true at VHF and UHF.
UHF PBR field trials were conducted in London in 1969. The results of test and
observations made by ITT over a 12 month period (later confirmed by the Ministry of
Posts and Telecommunications (MPT) in 1973) show that coverage at 12.5 kHz is
virtually indistinguishable from the coverage obtained from a 25 kHz system. In terms of
absolute range, impulsive interference, and speech quality the difference between the two
systems was barely perceptible subjectively.
It may be appropriate to conduct some subjective tests in the marine environment to
confirm the results of previous decades.
Recommendation 6.8: Use of 12.5 kHz technology on all ten UHF on-board
channels is recommended in order to minimise possible interference.
6.12.8 Socio economic factors
On-board equipment is generally low-cost; its replacement by new digital equipment
should not cause major economic problems. Should digital technology be implemented,
dual-mode equipment would be required for a transition period to permit communication
within and between ships that still use analogue techniques. It is assumed that the 11,000
or so SOLAS vessels in the red ensign fleet would have at least two UHF hand portable
transceivers on board, thus at approximately £200 per equipment the cost of replacement
of 25 kHz radios by new radios fitted with 12.5 kHz filters would be of the order of £6
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