RESEARCH DEPARTMENT

NEW BAND I TRANSMITTING AERIAL FOR THE WENVOE TELEVISION STATION

Technological Report No. E-ll4/l1 (1965/31)

G.H. ~illard, B.Sc., A.lnst.P., M.W. Greenway, M.Se., Grad.I.E.E., 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.

· .

GHM/CHD 7.4.66.

CORRIGENDUM

RESEARCH DEPARTMENT - BRITISH BROADCASTING CORPORATION

Technological Report No. E-1l4/11 (1965/31)

NEW BAND I TRANSMITTING AERIAL FOR THE WENVOE TELEVISION STATION

Page 1 - Substitute the following for the paragraph headed "Reserve Aerial":

"The reserve aerial, consisting of 1 tier of 6 dipoles at a mean height of 470 ft (143 m), is unchanged."

I

September 1965 Technological Report No. E-114/l1 0965/31)

NEW BAND I TRANSMITTING AERIAL FOR THE WENVOE TELEVISION STATION

INTRODUCTION

A new Band I aerial has been built on the column of the existing mast at Wenvoe in order to permit the erection of a u.h.f. aerial on a top mast. The new aerial came into service on 8th December 1964.

SUMMARY OF INSTALLATION

Site:

Support Structure:

General Arrangement:

Channel:

Aerial:

Reserve Aerial:

Power:

The site 1S 5 miles (8 Km) west-south-west of Cardiff, grid reference ST/111742, height 422 ft (129 m) a.~.s.l.

The support structure consists of a 715 ft (218 m) stayed mast. Up to a height of 610 ft (185 m) the mast is of triangular cross section with a side of 9 ft (2'75 m); above this height the cross-section is circular with a diameter of 6 ft 6 in (2 m). The mast is provided with three sets of stays, on bearings of 84°, 204° and 324° ErN.

See Fig. 1.

ChannelS with vertical polarization is used. sound carriers are not offset.

Vision and

The aerial, which is shown in Fig. 2, comprises 2 tiers each of six dipoles fed with equal co-phased currents. The dipoles are spaced O'25A from the cylinder and the inter­tier spacing is O'94A. The mean height of the aerial is 703 ft 1~ in (214 m), i.e. 34 ft 2~ in (10'4 m) lower than the original aerial. The aerial is fed wi th a single feeder, Hacketha1 type HF 4~ in (105 mm).

"The reserve aerial, consisting of 1 tier of 6 dipoles at a mean height of 470 ft (143 m), is unchanged."

A single transmitter run at 50 Kw is used. transmitter has a power of 5 Kw.

The reserve

Templet and horizontal radiation pattern (h.r"p.):

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

Gain:

Programme Link:

Note:

Acknowledgement:

REFERENCE

Fig. 3 shows the templet and the h.r.p. of the origInal aerial. If no mast stays were present, the new aerial would be omnidirectional to within ± 0'2 dB (Fig. 4). The effect of the mast stays is to give the h.r.p. shown in Fig. 5 and results in too large a variation compared with the original aerial" Accordingly, additional scattering conductors were fitted mid-way between the mast stays; the resulting h. r.p., which is that adopted, is compared wIth the original h.r.p. and the templet in Fig. 6. (See Note).

As the aerial comprises only two tiers, no gap filling of the v.r.p. is required.

Mean intrinsic gain

Deduct: loss in distribution feeders

Mean net gaIn

Deduct: loss in maIn feeder (type Hackethal HF 4~)

network loss

Mean effective gnin

The prcgraltllTIe js obtaIned by G.P.O. line.

2'8 dB

0'1 dR

2'7 dB

0-6 dB

0'1 dB 0-7 dB

--------

1he basic desigJl of the aerial w~s based on ll!c,!!surements on a one-tenth scale model of the whole aerial cOlJlplete wi th stays. It was originally proposed that the power of the transmitter should be increased by 1 dB in order to reduce the loss of field in certain directions compared with the old aerial. In the course of measurements comparing the performances of the old and new aerials it was discovered that the locked­coil rope feeder supplying the old aerial had 0'9 dB more attenuation than had been supposed and the increase of transmitter power was not therefore implemented.

The mechanical design, construction and setting to work of the aerial were carried out by Planning and Installation Department.

L Detailed information on the construction and dimensions of the aerial is glVen on the following drawings held by BBC Planning and Installation Department.

SMW

P.LD. SK 15907 H Transmitting dipoles

P. r. D. SK 15922 G Scattering elements

P.LD. Q103. 9.1 J Distribution feeders

3

752ft 6in (229'4m)---

Band I

736ft 6in (224 '5m)--- Band V

714ft 7in (217' 8m) - ......... - ..... 714ft 7in (217·8m)

703ft 1in (214·3m) --'1'---1'-

652ft Oin (198 0 7m)..<t:-- Band n 652ft Oin (198'7m)~t=--- Band II

610ft Oin (185' 9m)-- 610ft Oin (185'9m) ---

(a) Original arrangement (b) New arrangement

Fig.1. General arrangement of aerials on mast

324 0 stay N

/ dipola 294 0 dipola 354 0

1===0 dipola 540

scattaring alamant 144

0

(a) Plan

714ft 6~ in (217' aOm)------ ... -....,..----...,--..... 713ft 5in (217' 45m) --------j

3ft atin (H3m)

84 0 stay

~l

710ft O-lin (216' 42m)----· c::~I=~~1 7ft 6in max. (2, 29m)

J 703 ft 11in (214, 2 9m) =~==;~;;;;;;;;;;:r--i 702ft 2tin (214'04m)

tin (O '0127m)

9ft 10tin (3'01m)

696ft 2in (212'19m)

692ft 4 iin (211'03m)

6ft 6in (1'9Sm)

(b) Elevation

Fig. 2. Arrangement of new Band I aeria I

Fig 3. Tczmplczt for nczw cczrlc I VERTICAL POLARIZ ATION

ChannC21 5 (Vision" carriC2r 63'25Mc!s, Sound carrlC2r 66·75Mc/s)

--~ -- Maximum pC2rmissiblC2 E.R.P

------- Minimum dC2sirablC2 E.R.P (H.R.P of original QC2rial)

Unit fiC2ld corrC2sponds to an ER.P of 100kW

Fig. 4. Th<2or<ltlcal a<2rial without

horizontal radiation patt<2rn stays or scatt<2ring <21<2m<2nts

of

F i9. 5. Maasurad

with stays

horizontal radiation pattarn of aarial

but without scattaring alamants

Fig. 6 Measured horizontal radiation pattern of aarlal with stays and scattering elements

VERTICAL POLARIZATION

Channel 5 (Vision carrier 63·25 Mc/s, Sound carriczr 66·75 Mc/s)

Mean effective gain 2· OdB Transmittczr powczr 50kW Maan E.R.P 79kW

-- --- -- Maximum pczrmissible E. R.P ------ Minimum dasirabla E.R.P

Unit ficzld corrasponds to an E. R. P of 100kW.

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