1927-11-08 — Page 10

10

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RADIO TOPICS

BEGINNERS' GUIDE.maller and eventually disappear.

HOW BROADCAST SIGNALS

REACH OUR SET.

nre

From the T 250'À ̧a Anal neu- If we regard the ether as a pond, trallaed circuit leads to the main of the and the transmitting aerial as the transmitter, which is one centre of it, and if we regard the latest. Marconi MT OF, type, Both onergy put into the aerial as the these vaivos have been developed stone that diaturbs the water, we for ultra short wave transmission in hall understand how the other is conjunction with the well-known At the commencement of our disturbed electrically and how beam system, and are highly eff- subject we are forced to proceed waves are formed." Only, Instead clent, the latter being capable rather slowly, because it is at of radiating at ond level, wireless of disaipating up to one and a this stage that many important waves radiate in every direction, quarter kilowatts at 32.5 metres. matters that have a definite bear- They penetrate the thickest walls, The neriai current is on an average Ing on the science need to be pro- enter the earth, soar Into the four and a half to five amperes. perly explained. In attempting to clouds, and, as the recent Austra The high tension supply can be do this we are assisted by the large lian broadcast proves, even en-taken from a generator or from number of questions which have circle the world.

a full wave rectifying panel. On been put to us and which invari- Wireless waves keep their dis- the alter two MR 2 high- ably demonstrated a complete tance one from another and this power rectiflera giving 4,000 volts. ignorance of fundamentals.

distance is decided by the en- for the MT 9F and two MR 1 valves It is by no means common for gineers at the transmitting sta- giving 2,000 volts for the T 260A This duplica the novice to conjecture that actions who act the instructions of and modulators. tual sound waves are broadcast, the broadcasting authorities. If it tion of the power supply renders Jack of and that by using a very large is decreed that a

any station shall it very improbable that aerial more of this "sound" will be work on 500 metres it means that current will ariac.. received than by using a short every wave put out from that

An Aerial System.

wire.

aerial will be exactly 500 metres The last link in the system is the Let us say before going any fur-from the one before it and the one mortal which is about 80 feet long, ther that the sounds that are ser behind it.

and is suspended between the up in a broadcasting studio merely Whilst dealing with wave- house and a lattice steel mast 75 being influence the electrical character lengths, we will also refer to fre- feet high, the lead in of the waves of energy that leave quencies. It stands to reason that brought through the centre of a The the transmitting aerial. These two long waves take longer to put window two feet square. waves have to be received by the out than two short ones, since the situation is. ideal being very high listener and reconverted into audi-one in front has to go a long way and opon in all directions.

-trans- ble sound before anything can be before the other can be released. Having described the heard. This, in short, is a brief This is a very elementary way of mitter itself, we may turn to the explanation of wireless.

explaining how long waves are speech circuits and modulators. It is a long time since wired tele- said to have a low kilocyela fre- Most of the speech and music used graphy was invented and adopted. quency and short waves a high during the tests is relayed from a In the case of wired telegraphy a kilocycle frequency. If you look private studio about half a mile current is passed from place to through a B.B.C. atation list you away over private telephone line. place through a wire. When this will note that when the wave- In this room are the microphone Marconi-Reisz-the gramo- current is interrupted at the trans-langh is low the frequency is high, a

electrical mitting end it is naturally inter- and vice versa.

phone, fitted with an tha rupted at

receiving end But this variation in frequency pick-up, and the amplifiers. Three also. If these interruptions are so makes no difference whatever to or four stages of amplification 'us- arranged as to have significance the rapidity with which signals ing LS 6B and LS 5 valves, that is, if the interruptions take can be transmitted and received. followed by a bank of three LS5 the form of short and long periods, There is no means whatever of A's in parallel with three hundred usually referred to as dots and slowing down or speeding up a volte H. T. from H. T. accumula- dashes, and if both the transmit wireless transmission. A spoken tora. This bank is then coupled to ter and the receiver operator

word is received immediately it is the line by an ideal line trans- understand what the dashes and uttered, and it can be heard quick former. dots stand for-logical communica-er by wireless than by an actual tion can be established. In the stener seated at the back of a case of wired telephony the cur-fair-seized room in which the rent that passes from place to sounds are first made... place is also interrupted, but in a

We have now learnt that wire- different way. In this case the less is simply a science which en- an aerial diaphragm of the transmitting ables energy put into

be so influenced that the sound telephone influences the current, and received by suitable gear to dued at the receiving end in such be so influenced that the sound manner that the diaphragm of waves, first converted into elec the receiving gear is vibrated in rical influences, can be repro- duced after the electrical in- the same way and at the same speed and frequency as the trans-luences have been interpreted by

ano's mitting diaphragm, That being

set "Glasgow Weekly so, the receiving diaphragm sets up Herald."

and these influences are repro-

#

sound waves which are similar to the sound waves that actuated, the transmitting instrument. There is no miracle about this. Everything is straightforward and easy to understand.

Discovery of Aerials. Now, many years aga it was found that when a wire was charg- ed with energy in a certain way

EMPIRE BROADCASTING.

DESCRIPTION OF THE TRANS- MITTING APPARATUS.

fre

At the transmitter and a second, transformer steps up to the grid of one of the well-known DET 1 small transmitting valves, and the line is also,transformer coupled to a loud speaker for a check test. Signalling lamps and belle enable either end to call the other in the event of an adjustment being re- quired,

The amplified speech currentb from the DET 1 are applied to five or six T 250A valves in, parallel, fed with 4,000 volts and passing between two and three hundred milliamperes, which form the main modulating bank. Choke madula- tion in used, and the power avail- able allows of 40 to 50 per cent. modulation. A galvanometer is in- serted to check the grid current, and on no account is it allowed to swing beyond the limits imposed by good quality. A wavemeter is also used for checking the tone, which is quite as good as that of the average broadcast trans- mission.

Big Ben.

There is one exception. When Big Ben comes along the modula- tion is set "all out, for whatever may or may not be heard "Big Ben" must "get over."

it radiated the larger part, and The first real Empire broadcast- that the radiations occurred in all ing tests are being carried. out directions. This discovery war from 2 NM Caterham, owned and preliminary to another, which was operated by Mr. Gerald Marcuse. that another wire could be made to The object is to show whether it is behave in an opposite direction possible for a world-wide Empire It becames the receiving acrial link to be set up by 'a short-wave When both were tuned to sym-station in England, thus cement-

Now, although a studio half a pathise with one another the radia-ing the bonds which hold the mile away is very useful in the tion of the one affected the other so Dominions to the Old Country.

ordinary course of events, it is that the energy collected, when Quite obviously, writes a wire difficult to arrange for artists who suitably dealt with by appropriate less expert in the "Glasgow

are busy to go out the fifteen miles apparatus, could be made to Herald, the greatest care must be to it, and a studio in London has operate the diaphragm of 1 re-expended on such work if it is to been arranged for special oc- ceiving device, Then research be of any practical use, and as casions. Here A Marconi-Reisz went on, and it was discovered how 2 NM has recently been rebuilt on microphone, microphone amplifler speech could be made to operate a the most modern lines a descrip and "B" amplifier are used to re- diaphragm at the transmitting endtion of the general arrangement

lay speech and music over a special so that the radiations which would will be of interest.

Post Office line to the Caterham affect the gear at the other end Firstly, crystal control is

studio, whence it is again relayed would operate another diaphragm ployed, the crystal oscillating at

to the transmitter. which would set up sound waves 180 metres. An LS.GB valve, with

The equipment is practically (as in the case of a telephone dia-a neutradyned circuit, amplifies the identical with the used in the phragm), and thus reproduce voltages on to a frequency doubler, majority, of broadcasting stations

peech,

where the wave-length is reduced so that perfection of quality 18 This was accomplished; then to one quarter-that is 82.5 metres as-ured at every stage. Tone con- Brose another problem. If wireless by two more LS 5B's. These trol for raising the pitch to over- telephony was to be of any valves are supplied with 500 volts come any capacity effect in the at all, I would have to permit a high tension from the mains via line, volume control, voltage con- number of receiving aerials and a step-up transformer and two. U5 trol, all give flexiblity to meet any number of transmitting aerials to rectifying valves.

conditions. be in service at the same time. It is interesting to note that al- Transmissions would have to be though these are normally rated separated so that a receiver could for 250 volts maximum they have discriminate and tune in the mes stood up to the full 500 volts for sages that were wanted and not some considerable time. Two those that were undesired.

more stages employing a 150 Watt

цве

em-

It was when this problem was and a T 250A valve with neutralis- being, tackled that the wavelength ed circuits complete, the radio fre- system was devised and adopted. quency amplification.

Were it not for the use of varying wavelengths the ether would be a

Shielding Arrangements,

Rabel, and inter-communication The whole of the apparatus up to without wire would be an impos-this point is enclosed in a large sibibility.

copper, gauze cage four feet square

We cannot describe wavelengths and three feet high. Once set and better than by using an analogy adjusted it is sealed and can then which is always utilised for End be effected by no outside electric purpose, because there is no other field. These precautions are es so good. If a stone is thrown inte sential for maintaining a perfectly a pond ripples or tiny waves constant frequency, without which emanate from it and keep the it would be extremely dificult if same distance apart. As the rip-not impossible for the transmission ples get further away thy become, to be received,

YESTERDAY'S SOLUTION..

FORMOSA

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THE

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WEEKLY EDITION. OF THE "CHINA MAIL"

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1928

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WHAT DID YOU SAY ABOUT THOSE AWFUL

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I JUST SAW THE CASEYS, THEY ARE GOING TO AFRICA, TOO

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