,/ / ..

Research Department Report No.K.050

Serial No.1939/1?

NORWICH RELAY STATION

Prelimin~ry Report and proposals.

15th June 1939

Drgs. M.403. Mo 404. M.405.

(l) AREA TO BE SERVED, PRESENT SERVICE AND roPUlATION

The area considered in this report is the N.E. portion

of Norfolk including Norwich, Yarmouth and Lowestoft. The

field from the existing London Regional transmitter in that area

is too low to provide a service. and in addition there is

considerable fading. Whe~ the new London Regional transmitter

on higher power is working, the field will be increased, but

even with this increase it will be too low to provide an adequate

service J and while fading will be reduced it is probable that it

will still be too great for the service to be correctly termed

"fading free" over the whole area.

The following are the values of field expected in the

area under consideration from the existing and the new London

Regional transmitter~,on the present and new wavelengths.

Pbpulation figures are also given.

1IIIijili1lll1 300008788 Y ;

---~---~---- ------/

- 2 -

Field Strength (mv/metre) Town Population London Regional

Present wavelength New Wavelength Present power 125 kW 250 kW

Norwich 126,236 1.7 2.2 3.1

Yarmouth 56,771 1.9 2.4 3.4

Lowestoft 41,769 2.5 3.0 4.2

Kings Lynn 20,583 6.5 7.5 10~5

Cromer 4,176 < 1.0 < 1.0 ?

(2 ) PROPOSED RELAY STATION

A wavelength of 214 metres is available for a reiay

station in this district, and calculations have been made on a

basis of power of 15 kW to the aerial. For such a station it

is not thought worth while or necessary to carry out the usual'

site tests, as our previous experience should give us all the

information we re~uire by calculation.

The country is very flat and marshy, and it is

likely therefore that the conductivity will be good and the

attenuation low.

As the wavelength of 214 metres is shared by some

stations in other countries, namely Sweden and Italy, it is

necessary to reduce the field strength in these directions in

- 3 -

order to reduce the interference caused by our station. The

directions are approximately N.E. and S.E.

A system using a mast radiator of the order of 250 ft

in height with capacity top, such as is used at Penmon and

Redmoss, will be satisfactory, and would by itself give a

radiation efficiency corresponding to approximately EodovkW c = 3?0.

It would be necessary to use a parasitically excited reflector

approximately 3/8~ from the main aerial which would reduce the

field strength in the northeasterly and southeasterly directions

to approximately 1/4, and would increase the field in westerly,

northwesterly and southwesterly directions by approximately

20/25%. The polar diagram for such a system is shown attached.

CUrves have been calculated showing the field strength

to be expected from

(a) an aerial with a circular diagram

(b) the forward direction when using a reflector

(c) the directions of the minima when using a reflector

For each of these conditions two curves are shown, one

-13 13 for conductivity of 10 ,the other for O.? x 10- • In view

of the shape of the polar diagram and the fact that it is

necessary to serve Yarmouth and Lowestoft as well as Norwich,

it will be necessary to place a station nearer to Yarmouth and

- 4 -

Lowestoft than to Norwich. Reference to the curves will show

that for a distance of 16 miles in the forward direction, the

field strength should lie between 14 and 21 mv/metre. If we

allow for the additional attenuation over the town of Norwich

itself, we can consider that the field strength would vary between

7 and 15 mv/metre, which should be satisfactory, particularl¥

taking into account the low wavelength.

In view of the fact that either or both Yarmouth and

Lowestoft will be situated in one or both the minima of the

polar diagram, the field strength would have to be read from the

lower curves, and it Will be seen that a distance of 8/10 miles

is suitable. There will be less attenuation over the towns in

these cases, as the towns themselves are smaller, and their

distance in the path of the wave very small.

Referring to the sketch map attached, it will be seen

that possible sites are in the neighbourhood of;

(1) Haddiscoe {2} Fritton (3) Reedham (4) Acle (5) Burgh St. Margaret

Haddiscoe is about equi-distant from Yarmouth and

Lowestoft at 8 miles, but about 30 miles from Cromer where the

field strength would be in the neighbourhood of 3 or 4 mv/metre.

- 5 -

Bringing the station further N. to Burgh St. Margaret

or Acle would reduce the field strength in Lowestoft to about

4 mv/metre which is on the low side, while increasing the field

strength in Cromer to about 6 mY/metre.

It is probable, therefore, that we shall have to

compromise and site the station somewhere between Reedham and

Acle.

The question of the type of land will have to be

considered, as it will be inconvenient to build on very marshy

ground. The neighbourhoods mentioned above are on highe!

ground and avoid the marshes.

Kings Lynn will not of course be included in the

service area of the Norwich Relay Station, but would be included

in the service area of the new London Regional station which

should produce a field strength of about 7 0 5 mv/metre and a

non-fading Signal.

It should be pOinted out that were it possible to

use an aerial with a circular polar diagram, then the station

could be put slightly further N. possibly in the neighbourhood

of Homing or Ludham and provide a better service to the N.

coast of Norfolk by this means.

- 6 -

The field strengths calculated are probably slightly

on the pessimistic side as it is quite likely that the conductivity

in that area will be better than 10-13•

• K 11-JG'5 L YI-JN N

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