THE SERVICE AREA OF THE DOVER TELEVISION AND V. H. F SOUND TRAN'SM I TTER'S

Transcription

1 r RESEARCH DEPARTMENT THE SERVICE AREA OF THE DOVER TELEVISION AND V. H. F SOUND TRAN'SM I TTER'S Report No. K-158 ( 1962/50) C.P. Bell, B.Sc.(Eng.), Grad.I.E.E. (W. Proctor Wi I son)

2 This Report is the property of the British Broadeasting Corporation and aay Dot be reproduced in ady torm without the written permission of the Corporatlon.

3 Report No. K-158 THE SERVICE AREA OF THE DOVER TELEVISION AND V.H.F. SOUND TRANSMI~TERS Section Title Page SUMMARY. 1 1 INTRODUCTION. 1 2 GENERAL. 1 3 RESULTS 3.l. Television 3.2. V.H.F. Sound CONCLUSIONS.... APPENDIX 5

4 November 1962 Report No. K-158 ( 1962/50) THE SERVICE AREA OF THE DOVER TELEVISION AND V.H.F. SOUND TRANSMITTERS SUMMARY This report shows that while the Dover television transmitter provides a generally good service in East Kent, there are a few towns in the area which are still poorly served. The v.h.f. sound transmitter provides a satisfactory service to that part of Kent not served by Wrotham. 1. INTRODUCTION The Dover television and v.h.f. sound transmitters share the site of the Air Ministry Radio Station at Swingate, on the cliffs of Dover. The site height is 00 ft (122 m) above mean sea level. In April 1958 a temporary low-power television transmitter was brought into service. The aerials were mounted on the southernmost (No. 1) of the four existing radar towers, the mean aerial height being 300 ft (91 m) above ground level. In January 1961 a permanent low-power television service was introduced, radiating from an aerial mounted on a cantilever above No. 3 tower at the mean height of 375 ft (11 m) above ground level. A v.h.f. sound service commenced in August of the same year from an aerial interleaved with the Band I aerial. 2. GENERAL The permanent low-power television transmission on Channel 2 (vision Mc/s; sound 8 25 Mc/s) is vertically polarized and is provided by a 0 5 kw transmitter underrun at 0 27 kw driving an aerial which consists of two tiers each of two vertical dipoles carrying equal co-phased currents and interleaved with the Band II aerial. The minimum and maximum effective radiated powers (e.r.p.s) are 0 0 kw and 1 35 kw respectively. The horizontal radiation pattern (h.r.p.) is shown in Fig. 1. The three v.h.f. sound transmissions in Band II are provided by three pairs of 1 kw transmitters driving an aerial consisting of four tiers each of two tangential dipoles and triangular reflectors. The minimum and maximum e.r.p.s are 0 5 kw and 6 7 kw respectively. The h.r.p. is shown in Fig. 2. The Light, Third and Home programme frequencies are 90 0 Mc/s, 92 Mc/s and 9 Mc/s respectively. All field strength values quoted in this report are in decibels relative to 1 ~V/m (db(~v/m)).

5 2 6 60,,~-I I -~! \- --~ 'D' ~~ ~ I X ~ i i I -----~ C GP;,'EZ r----/// I,=-:;Jt!.,~"'f!ftW;~--'cg..,..,;,. _~~Bt1~---~ ~A'--~ _-o..._\ ~-~ Fig. DOVER: (MEASURED) Band I ~ Cl M i 8S, ---.l I SITE HEIGHT: ~OO ft (122 m) A.M.S.L. AERIAL HEIGHT: 375 ft (II~ m) A.G.L. MEAN LR.P.: 0'38 kw (O'O~ - 1'35 kw) POLARIZATION: VERTICAL AER I AL: N - TWO TIERS EACH OF TWO VERTICAL DIPOLES. H.R.P. AERIAL SECTION DRG.No. AE.~99 Notes 1. The contours represent the fi el d strength in decibels relative to 11J-V/m at 30 ft (9.1 m) above ground exceeded at 50% of receiving sites in a given locality. The value exceeded at 90% of receiving si tes may be as much as 10 db below the value indi cated by the contours parti cu I ar I y. in hi I I Y an d bu i I t-up areas. 2. x x_x Limit of service area free from percepti bl e interference from all U.K. co-channel transmitters for 90% of the time based on a protection ratio of Lt5 db, wi th a reduction of 10 db for c r 0 s s- p 0 I a r i z at ion and 10 d B for frequency offsets, allowance being made for recei vi ng aeri al di recti vi ty. - contours. Crystal Pal ace Lt. Folkestone station. s served by local rei ay

6 Fi g, 2 - DOVER: (MEASURED) Band II SITE HEI GHT: AERI AL HEI GHT: MEAN E. R. P. : ft (122 m) A.M. S. L. AERIAL: N -tp- 375 ft (IIII- m) A. G. L. 3' I kw (O' 5-6'7 kw) FOUR TIERS EACH OF TWO TANGENTIAL DIPOLES AND TRIANGULAR REFLECTORS. POLAR I ZA TI ON: HORIZONTAL H.R.P. AERIAL SECTION DRG.No. AE.500/2 Notes L The contours represent the field strength in decibels relative to 1 ~V/m at 30 ft (9 1m) above ground exceeded at ;0% of receiving sites in a given locality. The value exceeded at 90% of receiving sites may be as much as 10 db below the value indicated by the contours particularly in hilly and built-up areas. 2. Wrotham contours.

7 3. RESULTS 3.1. Television The results of the television survey are presented in a field strength contour map (Fig. 1), and details of the field strengths in towns measured which have a population of 1,000 or more are given in the Appendix. The contour map indicates that the service area limit is determined primarily by the high level of co-channel interference, field strengths of less than 56 db(~v/m) being liable to suffer multiple co-channel interference from other United Kingdom transmitters for more than 10~ of the time. The only major towns in this area having a median field strength less than 60 db(~v/m) are Margate and Westgate, both having 56 db(~v/m). Folkestone is served by the Creteway Down transmitter, but the towns of Hythe and Sandgate are at present poorly served, the Dover, Crystal Palace and Creteway Down transmitters providing low field strength values. The Herne Bay and Whitstable areas receive a comparable service from Dover and from Crystal Palace of between 6 db(~v/m) and 5 db(~v/m). Canterbury, which is poorly served by Crystal Palace with a median field strength of 1 db(~v/m), does not receive any improvement of service from the Dover transmitter V.H.F. Sound The service area of the v.h.f. sound transmitters is shown in the field strength contour map of Fig. 2, and details of the field strength measured in towns which have a population of 1,000 or more are given in the Appendix. Comparing the h.r.p.s of Band I and Band II transmissions, it will be seen that the latter radiates proportionally more power to the west to provide a service to the Folkestone area. The Wrotham and Dover v.h.f. transmitters collectively provide a satisfactory service to the whole of Kent, all major towns with the exceptions of Margate (with Westgate), Canterbury, Ashford and Hythe receiving a field strength of more than 66 db(~v/m). These towns are, nevertheless, provided with a satisfactory service by either Wrotham or Dover or a combination of both stations. The fringe area service provided by the Dover transmitter to East Sussex is of little significance as this area already receives an adequate service from the Wrotham transmitter.. CONCLUSIONS The Dover television transmitter provides a good service to most of East Kent, but there are a few small areas, notably Hythe, Canterbury and Ashford, where a satisfactory service is not yet provided. The v.h.f. sound transmitters provide a satisfactory service to the area not previously adequately served by Wrotham.

8 5 APPENDIX Town Field Strength (db(,uv/m) ) for Stated Percentage Locations Television V.H.F. Sound 10% 50% 90% 10% 50% 90% Ashford Aylesham Barham Battle Bethersden Bexb.ill Biddenden Birchington Broadstairs Canterbury Capel Charing Char th am Cheriton Cranbrook Deal and Walmer Derringstone Dover Dymchurch Eastry Elham Faversham 3 39 < Folkestone Goudhurst Harrietsham 0 3 Hastings and St. Leonards Hawkhurst Hawkinge Headcorn Herne Bay Hythe Kennington Lydd Lyminge

9 6 Town Field Strength(dB(~V/m)) for Stated Percentage Locations Television V.H.F. Sound 10% 50% 90% 10% 50% 90% Marden Margate (with Westgate) Minster New Romney Northiam Ramsgate Ringwould Rye 2 37 < Sandgate Sandhurst Sandwich Seasalter Si ttingbourne Staplehurst St. Margaret' s at Cliffe Sturry Tenterden Teynham Whitstable Willesborough Win gh am Woodchurch Wye BRR Printed by B.B.C. Research Department, Klngswood Warren, Tadworth, Surrey