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RESEARCH DEPARTMENT

U.H.F. TRANSMITTING AERIAL FOR THE BELMONT TELEVISION STATION

G.H. Millard, H.Sc., A.lnst.P.

Technological Report No. RA-3f1 UDC 62l. 396.712 1967/6

for Head of Research Department

This Report is the property of the British Broadcasting Corporation and may not be reproduced in any form without the written permission of the Corporation.

Th1s Report uses SI units in ftctor­d~n~e with B.S. dooument PO ~686.

February 1967. Technological Report No. RA-3f1 uoe 621.396.712 1967/6

V.H.F. TRANSMITTING AERIAL FOR THE BELMONT TELEVISION STATION

INTRODUCTION

A u.h.f. transmitting aerial for the East Lincolnshire area has been built on the support column of the ITA mast at Belmont. The aerial started trade tests on 5th November 1966 and full service on 19th November 1966.

SUMMARY OF INSTALLATION

Site:

Support Structure:

General Arrangement:

Channels:

Aerial:

Feeders:

Power:

The site is 12 km (7'5 miles) west-south-west of Louth, grid reference TF 217837, height 128 m (420 ft) a.o.d.

The aerial is supported by a 386 m (1265 ft) stayed mast. Up to a height of 274 m (900 ft), the mast is cylindrical with a diameter of 2'74 m (9 ft) and this section is equipped with a lift. Between 274 m(900 ft) and 336 m (1102 ft) the cross-section is triangular with a side of 1'98 m (6 ft 6 in.). Above 336 m (1102 ft) the cross-section is triangular with a side of 1'30 m (4 ft 3 in.>. The mast stays, which are attached to the corners of the triangular sections, are on bearings 61°,181° and 301 0 E.T.N.

See Fig. 1.

The aerial is designed to radiate on the two BBC channels, 22 and 28, of which the latter is used for the opening service (BBC-2). Both channels have negative offset.

The aerial comprises six tiers, each of six SA. panels, glvmg a total radiating length of 29'3A. at Channel 22 and 32'2A. at Channel 28. The panels of each tier are mounted in pairs on the faces of the support mast and are fed with co-phased currents. The aerial is protected from the weather by a 2'74 m (9 ft) diameter glass-fibre cylinder. Fig. 2 shows the arrangement of the panels on the mast and Fig. 3 shows the construction of each panel.

The mean height of the aerial is 348 m (1143 ft).

The arrangement of the distribution feeder is shown s chematically in Fig. 4. Each half of the aerial is connected to the transmitters by a feeder type F and G. 6.118 - 50.

Two 12' 5 kW vision transmitters and two 2- 5 kW sound transmitters will be provided for each channel; at present only those for Channel 28, manufactured by Pye, have been installed. Each transmitter will be run at the power required to give the maximum effective" radiated power (e.r.pJ of 500 kW permitted under the Stockholm Agreement.

Each vision transmitter is combined with a sound transmitter and the combined outputs are paralleled by means of a diplexer followed by a splitter transformer feeding the two halves of the aerial. This arrange­ment is employed to prevent differences between the modulation character­istics of the vision transmitters causing distortion of the received signal in areas corresponding to the aerial radiation pattern minima. A two­channel combining unit will be added later, as required.

2

Templet and horizontal radiation pattern Ou.p.):

Vertical radiation pattern (v.r.p.):

Gain:

Programme feed:

ACKNOWLEDGMENTS

The h.r.p. was required to be omni-directional with a maximum e.r.p. not exceeding 500 kW. The specified tolerance on the h.r.p. uniformity was ± 2'5 dB. The h.r.p.s at the vision carrier frequencies of the two opera­tional channels, which are shown in Figs. 5 and 6, are the mean of measurements made at the contractor's test site on each half of the full­scale aerial.

The v.r.p. was specified to be gapfilled with the maximum of radiation tilted below the horizontal; this is achieved by means of a phase dis tri­bution of the feed currents to the panels over the length of the aerial. The v.r.p.s obtained for each face, shown in Figs. 7-9, were computed from measurements of the amplitudes and phases of the feeds to the aerial panels, taken after erection.

Channel 22 28

dB dB

Mean intrinsic gain 15'0 15'0

Deduct aeriallosses~ dB dB

Gapfilling 1'2 1'0

Distribution feeder 0'2 0'2

Distribution transformers 0'1 1'5 0'1 1'3

Mean net gain 13'5 13'7

Deduct other losses:

'v1ain feeder (1240 ft) F and G 6.1/8 - 50 2'0 2'0

Feeder ground run (40 ft) 0'1 0'1

Diplexer and splitting transformer 0'1 2'2 0'1 2'2

Mean effective gain 11'3 11'5 --H.R.P. maximum/mean ratio 2'3 2'0

Maximum effective gain 13'6 13'5 -- -

Direct r~ception of Emley Moor. The recelvmg aerials consist of two G.S.V. double 10-element Vagi arrays mounted on the support mast at 73 m (240 ft) a.g.l. and are for use on Emley Moor Channel 51 (BBC-l) only. Each aerial is connected to a receiver at ground level by a feeder type HF 7/8 - 50

The mechanical and electrical design, construction and setting to work of the aerial were carried out by E.M.1. Electronics Ltd. The contracting authority was the BBC Transmitter Planning and Installation Department.

3

REFERENCES

Detailed information on the construction of the aerial panels is given on the following drawing held by Transmitter Planning and Installation Department:

L.H. Panel Assembly - BBC U.H.F. Belmont E.M.1. Electronics Ltd., Drawing No. 9A/D88750

JMP

N

t

BBC uhf a<lrial

BBC Band m a(lrial

BBC Band n atlrial

386m (1265ft)--382m (1252ft)--

3!57m (1173 ft) --

} 348m (1143ft)-f--

339m (1113 to--336m ('102tO --

30!5m (1000H)--

) 291m (~55 ft)-f-

277m (910ft) --274m (900ft) --

267m (875ft)

} 251 m (825 ft) --

'40m (4'OH'~;1t\

31 m (100 t t) ___ i~

3 m (10ft)----

provision for 1·30 m (4ft-3in) ITA uhf aerial

triangular mast

BBC uhf 2'74 m (9ft) diG. aerial wcathershicld

ITA Band m 1'98m (6ft 6in) aerial triangular mast

BBC Bandm 3'66m (12ft) dia.

aerial weathershield

BBC Band II aerial

2'74m (9ft) dia. mast fitted with lift

re - broadcast receiving aerials on Emley Moor

Fig. 1. Ganaral arrangamant of aarials on mast.

N

w~oth~rshi~ld

A

/

~-------- BOrn (4ft 3in)

"37rn (4ft 6in) rod.

Fig.2. Arrang(2m(2nt of uhf. a(2rial on th(2 support mast.

2'97m (9ft 9in)

464mm 1(18\in) I

I

[

t----j --

-- --

[

r----1 }---

[

00----. 140mm ( 5"t.in)

-~

711mm (2ft 4in)

Fig. 3. Construc.tion of oariol ponal.

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main feeder F 8. G 6'!-a-50

o aerial panal

tier

4

5

6

N

Fig. 5. Horizontal radiation patt<lrn: Chann<ll 22. HORIZONTAL POLARIZATION

Vision carrier 479·25 MHz, Sound carrier 485·25· MHz. Mean effective gain: 11·3dB Peak vision transmitt<lr power: 2x11 kW M<lan E.R.P.: 295 kW

- -- --Stockholm E.R.P. limit. Unit field corr<lsponds to an E.R.P. of 500kW

1

Fig. 6. Horizontal radiation patt<2rn: Chann<21 28 HORIZONTAL POLARIZATION

Vision carrier 527· 25 MHz, Sound carrier 533· 25 MHz. Mean effective gain: 11· 5 dB Peak vision transmittar power: 2 x 11 kW Mean E.R.P.: 315 dB ------ Stockholm ERP. limit

Unit field corresponds to an ERP of 500 kW

1'0

0·9

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4 6 8 10 12 14 16 angle below horizontal, degreczs

5 4 3 2 1·5 approximate range, km

Fig. 7. VClrtical radiation pattClrn on bClaring 001 0 ET.N (sidCl CA) Channczl 22 Channel 28 Specificzd minimum ficzld

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angl e below horizon1al, degrees

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4020 10 5 4 3 2 approximate range, km

Fig_ 8_ Vczrtical radiation pattczrn on bczarlng 1210 E.T.N. (sidcz AB) ------- Channal 22 --------- Channel 28

Specified minimum field.

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o·g

0'8

0-7

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1J ~0·5 -~

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,I \, [;~ r----- '- ~ ...... / '-...... .x / ' ..... '-o 2 4 6 8 10 12 14 16

angle below horizontal, degrees

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40 20 10 5 4 3 2 ',5 approximate range, km

Fig. 9. Vertical radiati on pattern on bearing 2410 E.T. N. (side BC) -- -- -- Channel 22 ------- - Channel 28

Specified minimum field

Printed by BBC Research Department, Kingswood Warren, Tadworth, Surrey