WIRELESS NOTES

Evening Star, Issue 18173, 13 January 1923, Page 15

WIRELESS NOTES

HOW TO ERECT THE AERIAL. Of alt the component parte of a wireless Ret, the aerial isl moot important. It is the aerial that intercepts the wireless waves as they pass through the ether and conveys tho electrical impute to the receiving set. Many amateurs spend much time and money endeavoring to improve the strength of tho conceits by alterations and extensions to their receiving apparatus when the fault lea in the aerial—that is, the amount of energy intercepted is not sufficient to give satisfactory results. The factora to ho considered in erecting an aerial are height, direction, and position, each of these having a very definite effect on tho strength ot too received signals. The radiation resistance of an aerial is expressed! by tho formula i Reaiskinoo equals 1,580 (height over waVo length), 2okras. And from this wo can sec that for a given wave length the height ia of vital Importance. For receiving tho local traiismiisiors an aeriai! 20ft high ia sufficient, but if tho concerts from other centres are desired this must be Increased considerably. Hero wo may mention that, since (lie wirokss waves follow tho curvature of tiro earth, the height above sea level Is not of such vital importance as tho height above tho ground or roof. For all-round 1 work, a height of 30ft to 40ft is recommended. Aerials may bo of two kinds—L aerials and T aerials, tho first typo consisting of a horizontal wire, with a leading-in wire at one cud, while tho second has the leading-in wire located at tho exact cen4.ro. The wave length of each may ho taken as approximately four and a-half times the length from tho free end to tho loading-ini wire, plus tho Jengtlt of tho lead-in,. This means that for the same -length of wire tho wave length of the .L aerial is greater than that of tho T aerial.

Both aerials receive most strongly from tho direction in which they lie, and tho D aerial receives mo;* strongly from tho direction of tho leading-in who cud. This directional effect should bo considered if it ia desired to receive tho concerts from other centres. TLma-ru, Oliristchurch, Wellington, and Auckland lie approximately north-east of Dunedin, so that tho aerial should point in this direction to give the strongest signals from tho northern stations.

Tho position of the aerial should, be selected) so that it is not screencdl by adjoining buildings. Galvanised iron roofs absorb tho waves, 'and all metallic bodies fshiad the aerial from tho direct action of tho ether waves. Wooden buildiuga hate no effect, so the wireless waves pass right through wood. Tho leading-in wire should ho as direct as possible until it enters- tho building. It should- be carefully insulated hero, and tho Fire Underwriters’ regulations specify that it must bo provided with an approved lightning protective device. located us near a* possible to the point where the wire enters tho building. Tho uso_ of a. grounding switch, though not essential, is desirable.

The earth wire should be ns short and as straight as possible, and soldered or bound io the nearest water pipe. It must not bo loit-j than No. 14 S.W.G. copper. If no water pipe is available, a pipe driven into tho earth or a burial plate will miffico. Alt connections from aerial to earth should bo uoldoicd.

For the recop Hon of concerts and) oil messages up to 600 moires a single wire will give results superior to two or three wires, and it should ho insulated at each end by a porcelain insulate". Tho length should be- not lc--« than 50ft and not more than 150 ft. For longer wave lengths a two-wire aerial will bu belter, and. it may bo longer than tho short wave aerial; but tho riuglo wire will meet most requirementa. We have seen dozens of aerials which by rearrangement might bo expected to increase the strength of signals considerably, and wo hope that these notes will assist the owners to obtain bettor results from their koi-s. Next week, wo will discuss tho receiving .apparatus, and will commence with tho tuning arrangements. GENERAL NEWS. IVo understand' that tho new Government regulations are now in print, and may bo cxptHod out very dliorlly. The suggested, fee for receiving licences is 5s per annum. For mid time past the Telegraph Department ha/s not been idium-g Uio provisional permits which w-ero previously granted, am! all those who are waiting for penniil-.ion to i red. Ijioir aerials will bo notified when tho icgaiatioiis are in force. One of our local experimenters who has done much valuable work informs us ho has been successful iu making his valve oscillate with 3 volte (two dry colls) cm the plate. This was receiving Pearl Harbor (Honolulu), 15.1’.M., over 1,000 metres wave k-ugth, ami tho eound through the loud speaker filled tho room. "With 12 Volts tiro valve could bo controlled quite readily. The Otago Radio Association, which holds the record in high 'power transmission, intends Lo conduct'Hi rther experiments during this month. Application has been nude for permission to send on Wednesday, tho 17th, riaUuday, 20ih, Wednesday, 24th, Friday, 26th, Wednesday, 31st, and Saturday, February 3rd. Wave length will bo 570 metres.