Precaution against Lightning.
Precaution aguinst shocks.
Foundation bolta.
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The most efficient working of the Station is to be on the 600 metre wave, the aerial circuit to have a natural wave length of 600 metres. The Station also to be capable of transmitting all waves from 800 to 2,000 metres. The range of reception to cover all wave lengths between 100 and 2,500 metres.
The above table of distances to be complied with when using the 600 metre wave for reception upon a crystal receiver the aerial circuit to tune to a normal wave of 600 metres.
The variation from each wave length not to exceed 5 per cent. measured according to wave length standard adopted by the British Post Office, but this limitation only to apply to the wave lengths used in effective transmission. Should any wave lengths outside these limits be emitted as subsidiary to the effective wave lengths they must not affect a similar receiving apparatus to that employed at the Station at a distance of 3 per cent. of the normal range of the Station when the receiving apparatus is tuned to the subsidiary wave.
5. Adequate precaution to be provided as approved by the Engineers against injury by lightning to operators and material both outside and inside the buildings, and to comprise apparatus for earthing by approved means the aerial conductors externally during thunderstorms.
6. Adequate safeguards to be provided as approved by the Engineers against electric shocks due to accidental contact with, or to development of faults in the high tension transmitting apparatus together with suitable means for cutting off the supply of power when effecting adjustments.
7. All necessary holding-down and foundation bolts plates and nuts to be provided.
MASTS.
8. Two masts to be provided each to be of the sectional steel type 203 ft. in height overall made up of 180 ft. of steel work surmounted by 23 ft. of wooden topmast. The steel sections to be made up in 10 ft. lengths bolted together with 1 in. bolts and weighing approximately 1.350 lbs. Each section to be dipped in preservative compound before despatch from the works and sufficient best quality oil paint to be supplied to enable one coating to be applied after erection.
The wooden topmasts to be 45 ft. long and 12 ins. square over the greater portion tapering at the top to 6 ins. diameter and to
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weigh approximately 2,000 lbs. each when fitted with the requisite steel hoops. Each wooden topmast to be thoroughly creosoted by the vacuum process.
Four anchorages with three guys fastened to each of them to be fitted for the support of each mast. The guys to be of 24 in. galvanised crucible steel wire rope and to be provided with rigging screws and porcelain strain insulators.
All necessary running rigging to be furnished to permit of handling the aerial, together with all the ironwork required for foundations and anchorages.
AERIAL.
9. The aerial to be of the multiple "T" type, suspended between the masts described above and provided with all necessary spreaders, strain insulators and guying out insulators. A suitable form of leading-in insulator to be provided and fitted on the Station- house to permit of a safe connection between the aerial and the apparatus inside the building. The lower end of the aerial structure to be guyed out in such a manner that no undue mechanical strain comes on this leading-in device. A special safety aerial earthing insulator to be furnished to enable the aerial to be earthed externally from inside the building during storms.
EARTH.
10. The earth to consist of a number of galvanised iron plates arranged on edge and completely buried in the ground in two semi- circles symmetrically placed on either side of the building. Galvanised iron earth wires to be run from each plate to points convenient for leading in to the building; from these points con- nection to be made with the earth terminal inside by means of insulated conducting cables.
As an extension of this system, if rendered necessary by the nature of the site, a number of wires to be carried out from the earth plates leading in the same direction as the horizontal wires of the aerial overhead and running the full length of the mast system a short distance below the surface of the ground.
The earth terminal to be of a special design, introducing a minute spark gap in the earth lead, across which the receiving apparatus is connected.
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