RESEARCH DEPARTMENT

V.H.F. TRANSMITTING AERIAL FOR TUE ROWRIDGE TELEVISION STATION

G.H. Millard, B.Sc., A.Inst.P.

Technological Report No. E-U9/l UDC 621. 396.712 1966/23

for Head of Research Department

This Report 1s the prop,}!'t) of the--ll Brit:lsh Broadcasting Corporation fJ,.nd

may not be reproduced in aD) for~

without t.he written pel'l"t1ission of the'

Corporation. j

May 1966 Technological Report No. E~119/1 UDe 621.396.712 1966/23

U.:H.:F. TRANSMITTING AERIAL FOR THE ROWRIDGE TELEVISION STATION

INTRODUCTION

A u.h.f.transmitting aerial for the Isle of Wight area has been built as a top mast on the existing 438 ft (133'5 m) mast at Rowridge The new aerial came into operation with trade transmissions on 18th December 1965 and started full service on 16th January 1966 •.

SUMMARY OF INSTALLATION

Site:

Supp ort Structure:

General Arrangement:

Channels:

Aerial:

Feeders:

Power:

The site is 3'5 miles (5'6 km) west-south-west of Newport, Isle of Wight, grid reference SZl447865, height 450 ft (137 m) a,m.s.L .

The aerial is supported by a 438 ft (133'5 m) stayed mast having a square cros s-section of 4 ft (1'22 m) side •. The stays are on bearings of 55 0

,

145 0, 235 0 and 325 0 ETN.

See Fig. 1.

The aerial is designed to radiate on four channels simultaneously •. The BBC channels are 24 and 31 of which the former is used for the opening service (BBC-2) .. The ITA channels are 21 and 27. Channel 24 is opera­ting with zero offset, Channels 21 and 27 will operate with negative off­set and Channel 31 with positive offset ..

The aeria1 1 compri ses six tiers each of four 4t-. panel s fed in phase rota~ tion. The power fed to the panels on mast faces C and D (bearings of maximum radiations 139 0 and 229 0 ETN respectively) is approximately one-tenth of that fed to the panels on mast faces A and B (bearings of maximum radiation 319 0 and 49 0 ETN respectively) •. The total radiating length of the aerial varies between 22'7t-.at Ch. 21 and 26'5t-.at Ch. 31. The panels are offset by 3.5/8 in. (92 mm) on a square of 35 in. (889'mm) side, and are supported within a load-bearing glassfibre cylinder of 5 ft (1'52 m) diameter •. Fig. 2 sh ows the arrangement of the panels inside the glassfibre cylinder and Fig. 3 shows the construction of each panel.

The mean height of the aerial is 467 ft (142 m) a.g.l.

The distribution feeder arrangement is shown schematically in Fig. 4. Each half of the aerial is connected to the transmitter by a feeder type F and G 4h - 50. The relative lengths of main and di stribution feeders are not the same for each half aerial, although the total length is the same. The actual lengths are as follows:

Distribution feeder, HF 7/8 Main feeder, F and G 4h

Upper half aerial

61 ft (18'6 m) 480 ft (146 m)

Lower half aerial

37 ft (11'3 m) 504 ft (153 m)

It is planned to use eventually two 25 kW vision transmitters and two 5 kW sound transmitte rs for each channel At present only those for Channel 24 have been installed.· Each transmitter will be run at the

2

Templet and horizontal radi ation pattern (h.r.p.):

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

Gain:

programme feed:

* i.e. the lowest tier.

power required to give the maximum effective radiated power (e.r.p.) per· mitted under agreements which were negotiated subsequent to the Stock· holm Plan.

The service has opened with one VISIOn and one sound transmitter fed into each half aerial but at a later date a diplexer and splitting trans­former will be added to minimize the effects of differences between the modulation characteristics of the vision transmitters. ' Similarly, two- and four-channel combinin~ units will be added later, as required. '

The h.f.p. was required to be directional in order to minimize interference to co-channel stations on the continent, with an e.r.p. not exceeding 500 kW at the maximum of the h.r.p. The templet and the h.r.p.s at the vision carrier frequencies of each operating channel are shown in Figs. 5-8. 'These h.r.p.s are the mean of measurements on each half of the final full-scale aerial. .

The performance on colour may be degraded on a bearing of 112 0 ETN on Ch. 21 and on a bearing of 132 0 ETN on Ch. 31, owing to deep minima at the colour subcarrier frequencies on these bearings. '

The V.f.p. was specified to be gapfilled and the maximu m of radiation to be tilted to 0'5 0 below the horizontal. Gapfilling is achieved by means of a phase distribution of the feed currents over the length of the aerial together with a physical tilt of the panels in Tier 6.* The V.f.p.S obtained for each face, shown in Figs. 9-12, were computed from measurements of the amplitudes and phases of the feeds to the aerial panels, taken after erection. Some degradation of the quality of reception is expected where the V.f.p.S show an appreciable transgression of the specification. '

Channel 21 24 27 31 dB dB dB dB

Mean intrinsic gain 14'2 14'4 14'6 14'8

Deduct aerial losses

Gapfilling 0'8 0'8 0'8 0'8 Distribution feeder** 0'4 0'5 0'5 0'5 Distribution transformers 0'1 0'1 0'1 0'1 Balance load 0'1 1'4 0'1 1'5 0'1 1'5 0'1 1'5

Mean net gain 12'8 12'9 13'1 13'3

Deduct other losses

Main feeder** 1'0 1'0 1'0 1'1 Feeder ground run, 30 ft ofH.F.3.1I8-50 0'1 0'1 0'1 0'1

Diplexer 0'1 0'1 0'1 0'1 Splitting transformer 0'1 1'3 0'1 1'3 0'1 1'3 0'1 1'3

Mean effective gain 11'5 11'6 11'8 12'0

H. R. P. maximum/mean ratio 4'5 4'1 4'1 3'8

Maximum eff ecti ve gain 16'0 15'7 15'9 15'8

G.P.O. Link

** As the lengths of main and distribution feeders to each half aerial differ, mean values of the attenuation are given.

3

ACKNOWLEDGEMENTS

The mechanical and electrical design, construction and setting to work of the aerial were carried· out by the Marconi Co. Ltd .. The contracting authority was the BBC Transmitter Planning and Installation Department.

REFERENCE

S'vIW

1. More detailed information on the construction and dimensions of the aerial is given on the following drawings held by Transmi tter Planning and Installation Department:

Band IV Panel Aerial Assembly similar to

Marconi drawing T80-1439 Marconi drawing BT 02-8240 Sheets 1 and 2.

491ft (149·6m) ---------

467ft (142·3m) 1:. --------

443ft (135·0m) ---------438ft (133· 5m) ---------

387ft (118·0m) t ---------,----

342ft (104·2m) ---------

296ft (90·2m) rf:. --------

249ft (75·9m) ---------

tt

I

Band I7

Band I

Band II

Fig.1. General arrangement of aerials on mast.

r-""-(J) ..-r-

W

....-L-0 0-Cj er

=1-lightning /'

conductor

35in (889mm)

+

glass fibre cylinder, 5ft (1· 52m) diameter

Fig.2. ArrangClmClnt of aClrial panClls.

+

+

7ft 6'5in (2'30m)

11 in (279mm)

1""'1 <r.---- 24in ---"~I (610mm)

Fig.3. Construction of singlcz panczl.

[

5in (127mm)

I I . . lh-

.......::

I-I---

J

t---I---

J

t---I---

t---I---

~ F

::0 ('\) u o ., r+

face:

nominal currents:

tier:

4

5

6

A B C D

1·0/.Q° 1.0mO 0'3/180° 0,3/270°

r--

'-

r--

'-

r-

'-

~

r--o ~ transformer] ;--

'-

trans former r--

'--

transformer r-

'-

r----transformer J---

L-

I transformer ..--

L...--

transformer ~

I--

balance load

'VI (\I' ~

"'----_/ Jl"i"~

"'_ ___ ..I

diplexer

main feeder F and G 4~-50

Fig. 4. Schematic of distribution fe<lder arrangement (lower half a<lrial)

r-

'-

r-

'-

r-

'-

Fig. 5. Horizontal radiation pat tarn : Channczl 21 HORIZONTAL POLARIZATION

Vision carriar 471·25 M Hz, Sound carriar 477·25 MHz Maan aff(lctiva gain :11-5dB - -E.R.P. lim·ft agraad post Stock holm Paok vision tronsmittar power :2x6·5kW Mean E.R. P.: 1S0kW

Unit field corresponds to an E.R.P. of 500kW

-.. " "'C C

r

)

L >

Fig. 6. Horizontal radiation pattern: Channel 24 HORIZONTAL POLARIZATION

Vision carri12r 495· 25MHz , Sound carrl12r 501· 25MHz M12an 12ff12ctlv12 ga'ln: 11·6dB - - E.R.P. limit agr1212d po~t Stockholm P12ak vision transmitt12r pow12r: 2x 7kW M12an E .R. P. : 200kW

unit fi12ld corr12~POnd5 to an E.R.P. of 500kW

Fig.7.Horizontal radiation pattarn ~ Channal 27 HORIZONTAL POLARIZATION

Vision carriar 519·25 MHz, Sound carriar 525·25 MHz Maon affactiva gain: 11·8dB • - - E.R:Plimlt agraad post Stockholm Paak vision transmittar powar: 2x6'5kW Maan E.R.P. : 200kW

Unit fiald corrasponds to an E.R.P. of 500kW

liJ

N

Fig.B. Horizontal radiation pattelrn: Channell 31 HORIZONTAL POLARIZATION

Vision carriar 551·25 MHz • Sound carriar 557· 25MHz Maan affactiva gain: 12·0dB - - E.R.P limit agraad post Stockholm Paak vision transmittar powar: 2x6·5kW Maan E.R. P. : 210kW

Unit fiald corrasponds to an E.R.P. of 500kW

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anglC2 bC2low horizontal, dC2grlZC2s

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502010 5 4 3 2 approximatlZ ranga, km

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14 16

Fig. 9. Vczrtical radiation pattczrn on bczaring 49°EJ.N.( faccz B) • • ChannlZl 21 ChannlZl 24

--- - ChannlZl 27 - - -- - Channal 31 --- Spacifiad minimum fiald

O·9~~--+_~--~--r--+--~~---r--+--+--~--r-_r--+_~

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\ ~j rr~\ 0·3 I---t----t-i, tt=""-/-:+H---flt-t-\~' \-+--1----+---+--+--+--+----t---1r---+----+----i

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54 ,y

angla balow horizontal. dagraas I I

3 2 approximata rang~,k.m

14 16

Fig.10.vczrtical radiation pattczrn on bczaring 1390 E.T.N. (faccz C) • • Channczl 21 Channczl 24

- - - Channczl 27 - - - - - - Channczl 31 - - - Spczcificzd minimum fillld

1-0

~ 0-9

0·8

0·7

.c c;, 0-6 c Cl "­.... C/l

"Cl

_"§i 0-5 .... Cl > .... o

~ 0-4

0-3

0·2

0·1

o o

, \ ,

,I , , , , , , , , , , \ 1

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l-Ll\ , / vf\r-.. ~ IV 11 ~\ \ , • U '\ \' ,

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\",- , r--I~ .... .'. ~ :.l. ~~ v

2 4 6 8 10 12 14 16 angla b<2low horizontal, dagraas

5 ~~!~! __ ~I ____________ ~l __________________________ _

43 2 1 approximata ranga ,km

Fig.11.V<2rtical radiation patt<2rn on b<2aring 229°EJ.N.(fac<2 D) • • Channl2l 21 Channl2l 24 --- Channl2l 27 ------- Channal 31

---- Spacifiad minimum fiald

1·0

0'9

0·8

0·7

£.

~ 0·6 c:: ~ L. ..... III

TI

.~ 0'5 -~

.~ ..... o ~ L. 0.4

n ~

\ ,

, ~

, \ \ 0'3 \,\1

0·2

0·1

o o

I I I

5020 10

~ t ",V ''',

2

,",

It l\ '7\ \\ I \'

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~ j ~ .....,.. }f,. 1\ " X) ~ ~ ~ )C''"") " /

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~~ \,l .. " W. /' \~~ . X') [J" ~l V, 1\ '-1

V 1 J' " ..... .A .-' 1\ .:LL ~" .~ - ~

6 8 10 12 14 16 anglll billow horizontal , dllgrll~s

I

2 approximatll rangll, km

Fig.12. Vflrtical radiation pattflrn on bflaring 3190 ET.N. (facfl A)

• • ChannC2\ 21 ChannC2\ 24

--- ChannC2\ 27 ------ ChannC2\ 31

--- SpC2cifiC2d minimum fiC2\d

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