1930-12-04 — Page 2

HONG KONG DAILY PRESS, THURSDAY, DECEMBER 4, 1930.

EARLY WIRELESS

RADIO

FEATURES

EXPERIMENTS.

WORK OF SOME OF THE PIONEERS.

MESSAGES SENT ACROSS RIVER TAY IN 1843.

It is some le years since broadcasting became a practical proposition and about thirty. years since wireless telegraphy was used for commercial purposes. Throughout this period the name of Marconi has been largely associated with most of its developments, so much so that As a matter of fact he Senator Marconi is looked upon by many as the inventor of wireless. was the first to make wireless a praction!' means of communication rather than a laboratory experiment. Many other names must be associated with the carlier work.

THE LEYDEN JÁR.

making the single wire earth return telegraphic circuit a practical suc+ cess. The purely "wireless" idea was only good for about to feet. In 1842, Morse, a name well-known in connection with code telegraphy,

To an extent wireless communica- tion is dependent upon the funda- mental researches of such men as Gilbert, Cavendish, Coulomb, Gal- transmitted messages across a canal Veni, Volta, Ampere, Ohm, Fara-without any, metallic connection be- day, and a multitude of others such as Cuncus, who in 1746 discovered the Leyden Jar, a form of the con- denser which plays such an import ant part in modern wireless com. mmunication. Their work cannot be detailed, but its general electrical importance may be gauged from the fact that most of their names are honoured by having various units of electricity and magnetism called

after them.

Perhaps the carliest attempt to establish telegraphic communication without wires was that of Steinheil, in 1838. He made use of the earth, but the results were not of much practical value from the "wireless" point of view, although he made an important contribution, to the advance of ordinary telegraphy by

Thi

tween the sending and receiving stations. A year later one by the name of J. B. Lindsay transmitted messages in a similar manner across the River Tay, covering a distance of two miles successfully. All these results, however, were really chtain- ed by conduction, that is, the direct

passage of current.

Other attempts were made to transmit signals by induction, both electro-static and electro-dyasmic, and successful systems were evolved ulilising both means. Edison (1885) by static induction was able to make vae of the ordinary telegraph-lines ruaning alongside a railway and could transmit both telegraphic and telaphonic messages to and from trains in motion without-any metal lie contact with the wire system.

Existence of Waves Suspected.

From 1884 onwards, Sir Williain Preece carried out many experi- moats on communication by induc tion. He generally arranged long wires and caused currents to flow through them. Corresponding cur- rents were induced in somewhat similar circuits, and so the signals were transmitted. It was rather like having a transformer with its primary and secondary well separ ated. For years this system was used commercially from islands to the mainland in various parts of the British Isles. Leakage currents

were also used.

The existence of waves of the nature which we use was apparently noticed by Ileary as long ago as

and

1842, when he remarked on the dia turbing effects of a spark, and com. pared the disturbance to light. In 1872 M. Loomie is eaid to have sent signals by means of electric waves over distance of 10 miles from a About wire elevated by a kite. 1890 Professor D. E. Hughes un- doubtedly caused the emission of

invisible electric waves" evolved a means for detecting such Unfortunately for him le waves. did not publish the results of his experiments until 1800. He was too late then. A. D. Doibear, of Bos ton, very nearly achieved practical success in 1892. Actually the waves were not produced until 1898 by Heinrich Hertz. In 1884, Clerk Maxwell, insing his theories upon the experimentai work of Faraday, assumed the existence of the ether

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existence of electro-magnelie waves therein.

Maxwell said that if these waves could be generated they would travel with the,, velocity of light; that light was an electro-magnetic phenomenon and not mechanical; that the refractive properties of certain substances were intimately related to their dielectric proper ties and that conductors of elec tricity must be opaque to light.

For 24 years after Maxwell's pre. diction no one proved his state- ments experimentally, Hertz, as stated above, being the first, al though several had gone very close La it, Sir Oliver Lodge, for in- atance, in 1887-8 produced waves by discharging Leyden Jars, and mea. sured the wave lengths by causing them to run along guiding wires. Te did not quite do it, however,

The Work of Hertz.

Hertz in his experiments took two metal plates to which wires.or rods were attached and which end- ed in metal knobs. The two knobs formed a spark gap across which a Each spark was made to pass. spark (supplied from an induction

coil) caused oscillatory currents in the oscillator (the two plates) of a rapidly diminishing amplitude or strength, and the currents passed backward and forward across the gap until their supply of energy became exhausted,

The resulting qacillations set up disturbances in the ether, which created a series of waves, which took with them some of the energy The supplied to the oscillator.

waves so created were detected by an arrangement which he called a resonator, which is one form was an exact counterpart of the cecilla- tor. Having the same dimensions, the currents "sot ap in it had the same period of oscillation, and when it was placed in proximity to the oscillator, oscillations were set up, and sparks occurred between the

nobs of the resonator.

Hertz also studied the properties of these waves. He found out that the wares obeyed the laws govern ng light waves, and showed experi mentally, that they travelled at the velocity of light, They could be reflected from metal sheets placed against the wall of the laboratory. and the reflected wavo interfered with that coming from the oscilla tor, setting up standing waves, the neaks and troughs of which could, be traced out by moving a wire loop detector to and fro batween the oscillator and the reflector, the Lanarks at the knobs of the detector disappunting mu reappearing ar certain points.

(Continued on Page 3)

HAVE YOU HEARD THESE?

50.

Here are sis of long-waya had short-wave stations which should be picked up by anyons

la Hong Kong who has a mode- rately good set mitable for re- colving such signals. Success in pleking up these stations also depends very largely upon tay- ourable atmospheric conditions, Readers are invited to add 10 this list should they succeed in picking up. any station not in- cluded in either of these Hats.

37. $9.4

LONG-WAVE STATIONS.

Wavo length (Metres) Station

200 Manila 277 Shanghai 280 Tientsin 310 Shanghai 320 Faping 345 0

Coll Kilo-

Sign cycle

K.Z.I.B. 1,153 K.B.M.8. 1,035 C.R.C. 1,070 K.R.C. 0.0.P.K. J.0.A.K. 870 J.O.F.E. -650 Hong

Kong Z.B.W.

V.U.B. Bombay

301 Sapporo 300 Kolio 370 Nagoya 370.4 Calcutta

840 840 J.O.L.K. 890

JO.D.K. 820

J.O.C.K, 810

V.U.C. 800.9

380 Kumamoto J.O.G.K. 790

390 Sendai

365 Dairen

398 Rangoon

400. Osako 410 Canton 413 Manila

SHORT-WAVE STATIONS.

Kito

CYCLES

J.O.H.K. 770 J.D.A.K. 760 V.U.E. 754 3.0.B.K 750

O.M.B.

732 K.Z.R.M. 728

Tra (Hoxo Koxo) OF WORKING

4,484 Mon, Wed.'& Fri, 0 p.m. & 2 mm 4,900 6-10 p.

5,201 Not regular

0,000 Tue, Thura, Sat., 8 pan.

7,142 Dally 0.80 p.m.11 p.m.

7,310) Not regalar

8,108 Tues. & Fri, 9 pm-1 ..

9,230 Not regular

1,603 Not regular

W.2.X.A.F. 8,530 Dally 7 a.m,

STATION-

CALL SIGN

07.85 60.12

Dobintz (Germany)

A.F.K.

Khabarovsk (Russia)

RA.97.

53.7

Navon

A.G.J.

MORCOW

R.MN.

48.15

Roms

1 M.A.

6.806 Sunday midnight

42.

Porth

LA.G.

41.3

Blogapore

V.8.1.A.E.

69.8

Kootwijk (Holland)

P.CL.

7,730 Daily 1 p.m.

Bangkok (Siam)

HS4PJ.

Bydooy

Z.B.L.

31.56 Melbourne

a.L.0.

81.48 Schenectady

$1.20

Eindhovon (Holland)

P.C.J.

31.28 81.

·28.6 27,8 25.68

Sydney

2.F.C.

Nairobi (Kozya}

LO.

Bydney

2.M.E.

10,526 Net regular

Bandoorg

P.L R.

Chelmsford (England)) 0.8.W.

24.5 28.35

Manila

K.J.X.E.

Schenectady

W.2.X.0,

19,88 IB.4 12.4

Bandoesg

P.L.G.

Kootwijk (Holland)

P.C.L.

Bandoong

P.L.F.

18.50

Bangkok

18.3

Kootwijk (Holland):

P.C.K

15.74 Bandoeng. 18.5

P.L E.

Nancy (France)

19,851 Dally 8 am,

W.8.X.K.

13.93 Pittsburg

H.6.1.P.J.

8,050 Fri. 8 m., Sat, 3 am, & 10 am.

1,500 Not regular

0,677 Midnight daily

11,20 Midnight-an. daily

11,761 7.80 p.m. & 8 a.m. daily, excopt. Saturday and Sunday

12,240 Nightly

12,850 4m. Wod., F., Bat.

10,102 Daily 8.30 p.m. to midnight -16,304 | Daily 7 p.m.

17,280 Daily 8 pm to midnight

17,761 Sunday 7 p.m. & midnight 18,404.Each afternpos,

19,220 Daily 6.30-7 pm.

21,540 Not regular

[Allowance must be made for "summer-time" in most Euro- pean countries, which is one hour ahead of true time.]·

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