1931-06-25 — Page 2

HONG KONG DAILY PRESS. THURSDAY, JUNE 25, 1931.

Listen -

If

RADIO

FEATURES

HOW A SUPERHETERODYNE WORKS.

WHY A SECOND DETECTOR IS NEEDED IN SYSTEM OF

AMPLIFICATION.

have now taken. a semi-circular lump out of the Balcony, so that the entire orchestra will be out in this open floor space.

mendations, great importance attached to the deliberations as ự possible outcome is a complete reshuffle of European wave lengths. This, howoyor, would not be do complished until after the, Madrid Radio conference next year,

LOOK TO YOUR AFRIAL. At this time of the year anything from a spider to a flash of light.

cause trouble yout

Ready to Mora, The whole, of Savoy Hill's staff, equipment, furniture, "and every Most people have a general idea maximum again, is equal to the relatively slow variation in ampli- thing will go to Portland-place as as to the functioning of a super-difference between the frequencies.tude produced by the transmitter, soon as Broadcasting, House is heterodyne receiver. The essentia! sy Kot-An Entirely separate and therefore, these speech modu- ready. The earliest move may be you want Best British principle is that the main portion

iations are carried right through to expected towards the end of ing the end of the intermediate fre- Angust, for the alteratious to the big studio will not cause any delay queney amplifier.

in moving.

Components, it is undoubtedly

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of the amplification, and the selec tion of the required station; is carried out at a fixed, wavelength; which is quite different from the wavelength on which one is receiv ing. By an apparently mysterions process the incoming signals are converted into this other wave length as and when required. The advantage of the system is, of

course, that one can make the intermediate amplified selective and highly powerful by incorporating Hoveral stages without the extra number of tuning controle which this would normally involve, since the intermediate stages are of

tune,

Elle

Oscillation.

Now.comes

4

most important point. We have just aren. that this Beating or heterodyning arises from variation in the amplitude of the current, and is not an entirely separate oscillation. But we can not hear the original high-frequency oscillation, which is far beyond the limit of audibility, and therefore

neither can we hear the resultant current produced by the moving of the high frequencies. The effect is

If

in a telephone transmission. one places a pair of telephones in

This possibility will be made clear if one considers the relative frequencies. Our beat frequency is The speech fre

50,000 cycles. quency, however, even at the upper frequencies, takes place about five

thousand times a second and, there-

Building is actually well ahead of contract time, and by the end of the autumn Savoy Hill will doubtless be deserted. Meanwhile the next stop at Broadcasting House will be to get the wiring

fore, during one complete five done. Electric lighting wires al exactly the same as the modulation thousand-cycle note we have one ready measure about 50 miles. Soon hundred variations of the gokild-the radio engineers will do their eyele carrier wave. It will be quite clear that the low-frequency varia. tion is so slow, relatively speaking,

fixed the aerial lead of a set no signals can be heard, even though the sta- The simplest way to explain fretion is quite close by. quency conversion is to work back from ordinary well-known facts. We overcome this defect in an that the simple arguments which For example, if one's receiver is ordinary telephone transmission by have been developed are not affect allowed to oscillate when it is rectifying. That is to say, we reed at all, and we can consider the tuned approximately to any given move the negative portion of the process taking place just as has station, a whistle will be heard, current by inserting some form of due to "heterodyning" or beating conductor which only allows the between the local oscillation and current to flow in one direction, the carrier wave of the particular Then the state of affairs is quite transmission being received. The altered because although the im pitch of this whistle can be varied pulses still follow one another at an exceedingly rapid rate, they are Ts one alters the tune of one's re

now all in the same direction, Thus, we are left at the end veiver.

giving a definite mean or average of the intermediate-frequency am value. What is more, this valus:

15

Beat Frequencies,

already been described, except for the fact that the amplitude of the whole complex oscillation in grad ually varying in intensity in accord ance with the speech frequencies.

little bit and add probably another 50 miles of wire. Yes. The B.B.C.

do call it "wireless"!

•

DENMARK DISCUSSIONS,

Mr. Noel Ashbridge, chief en gineer of the B.B.C., accompanied by an assistant, has gone to Copenhagen, where he is taking part in international discussions on wave length problema. Oficially he is representing the International Broadcasting Union, but no doubt

he will be able to negotiate on be half of the B.B.C. as well.

aerial.

Natura, in fact, seems to be re- sorting to all sorts of subtleties in

to

order to prevent people listening.

She sende ants

nibble away at

the foot of the aerial polo; trees grow so quickly that they touch tha wire and cause a short circuit to earth; various insects chew through rope halyarda; sunshine splits woodwork and ruins exposed cbonite lead-in tubes, and even birds settle on the aerial and some- times pect at it. Brute force-in the form of lightning or “thunder-

ing short-circuit caused by damp bolt"-is contrasted with a mystify-

spider webs

AZ LYSTERY FAULTS.

If, therefore, you want to spend a proftable half-hour examine your aerial closely and so avoid my sterious faults.

It is a good plan to take the aerial wire down and clean the in- rulators. Soot on the actual wire does not matter so much (except that the wire gradually, corrodes)," but on the insulators it may be

can only make recom- Bible,

The meeting is held by the Inter- very detrimental to good reception.. national Consulting Committee on If no lightning protector is pro- This whistle arises because we will vary if the strength of the plifier with a strong 50-kilocycle Radio Communiontion, and alvided instal one as quickly as pos have two oscillations. One is re- oscillation is changed. In the cass carrier, modulated by speech fre- though it ceived from the, distant transmis of a telephony transmission the quencies just like an ordinary car aion, and the other is generated strength of the oscillation is con-rier wave, Now 60 kiloeycles is locally in the receiver. The two tinually altering in accordance still an inaudible frequency, and oscillations are not exactly of the with the speech or music impress

+7

Fectify

same frequency, and therefore they ed at the transmitter, we are thus therefore, we are unable to detect interfere with one another, and pro-able to hear aptech current in the low-freqency modulation unless duce beats which in the present in telephone receiver. In the same we once again. Therefore, stance are of an audible frequency way, if we have two oscillations it is necessary to have a second The actual frequency of the beat heterodyning one another and pro- is equal to the difference between ducing beats as we have just dis- rectifier at the end of the inter the frequency of the two oscilla cussed, we can only detect these mediato amplißer, as a result of tions, so that as we bring the re-beats as long as we rectify the re which the mean current in the ceiver more and more into tune sultant current, so that the mean

anode circuit varies in accordance with the distant transmission, the value is capable of varying.

with the speech frequencies, as is pitch of the best note gradually

the case of an ordinary radio re- falls, until it becomes inaudible.

An oscillation is a current which

ceiver. At this point, therefore, we flows first in one direction and then

by puss the 60-kilocycle oscillation in the other. If we have two such be heard after the resultant current to earth, since we have now finish- currents, both of which start off has been rectified, we can now pro ed with it, and we are left with together, clearly they will add to: ceed one stage farther, and gether, and we will have a current sider the case of the super-bete- of twice the amplitude, flowing first rodyne. By arranging that the in one direction and then in the local oscillation is considerably other an before."

different from the incoming oscil;] lation, say, perhaps, 50 kilocycles different, we can obtain a beat fre- quency of so kilocycles.

Having appreciated, this import ant point, namely, that the. beat frequency produced by mixing two high-frequency oscillations can only

con-

pure low-frequency which may be magnified in the ordinary manner and applied to the loud-speaker.

TOO MUCH BALCONY IN NEW STUDIO.

ALTERATIONS AT B.B.C.!! NEW HOME.

If one of the currents, however, is oscillating at a slightly different frequency, it will gradually fall out of step. In certain parts of the

Intermediate Frequency, cycle, one current will subtract from the other instead of adding

This is quite above the audibles de pri to it, this reaching its climax at limit, actually corresponding to a the point where the two currents wavelength of 6,000 metres. Thus, are exactly out of step. At such if we rectify the resultant oscilla a point, one current will be at a tion we shall obtain our original

beat maximum in one direction, while high-frequency oscillation, modu the other current will be a maximumlated at a frequency of to kila in the opposite direction, and the cycles. We have now finished with Pedestal Heater total effect will be zero. Our re- the original high-frequency oscilla Supplied with a yds.

sultant current, therefore, varies tion and, therefore, we by-pass it from twice the normal value to zero to earth in some suitable manner, and back again.

leaving ourselves with the 50 kilo cyala variations, which are presed

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HAVE, YOU HEARD THESE?

Here are lists of long-wave- and short-wave stations which should be picked up by anyone. in Hong Kong who has a moda. rately good sol suitable for re- ceiving such signals. Success in picking up these stations also depends very largely upon curable atmospheric conditions. Headers are invited to add to this lat should they succeed in picking up any station not ip- oluded in either of these lists.

LONG-WAVE STATIONS.

Call Kilo Bigo

cyclo

Wave length

(Metres) Station

260 Manila

EZIE 1.

1,083

277 Shanghai K.S.M.S. -346 Tokyo J.0.A.K. 870

353 Hiroshima 1.0.F.K. 305 Hong Kong Z.B.W, 846 357.1 Bombay

* 381 Sapporo

300 Keijo

$50

#

V.U.B. 840

J.O:LK. 830

J.O.D.K. 820

370 Nagoya J.0.0.K. 810

· 370.4-Calcutta ---- V.U.O -----800.9 380 Kumamoto J.O.G.K. 700. 300 Sendai J.O.H.K. TWO J.Q.A.K.. 1700. J.O.B.E 750 .C.M.B. 738 K.Z.R.M. 825

305. Dairen

400. Osaka "

410.Canton. 480 Manila SHORT-WAVE STATIONS.

STATION

CALL SIGN

Thus (HONG Kоka) · or Working

4,424 Mon., Wod & Fri., 8 p.m. 4'2 1 4,000 810 p.m.

5,291 Not regular

Tam Thurs., Sat., 8 p.. 6,808 Sunday midnight 7,142 Daily 4.80 p.m. & 11 pm,

07.68 Doblats (Germany)' (0.12 | Khabarovsk (Russia) RA07. BAT Nautn

AFK

AGI

50. 43.8

Mosco

*6,000

LMA

413

Porth Bingapore 88.8 Kootwijk (Holland) 87. Bangkok (Slam) 32.6

Sydney Melbourne

42,

a

730 Dally 11 p.w.

LoudBK7,810 Not regular HSLPJ.

8,103 | Tuos, & F., 9 p.m.-1 am. 3.8.£.!!

Not regular S.L.Q... 9,593, Not regular W.2.X.A.F. 8,630 Daily 7 m. P.C.J.

The completion of the super- studio at Broadcasting House. Landon has been set back a week 31,48 Schnootady or two owing to alterations and 81.20 Eindhoven (Holland)

81.28 Sydney modifications which have been 81, Kairobi (Kanys)

28.6 Bydroy found necessĖTY,

Bandoong 27.6

25.68 Chelmsford (England); 5.8.W.

It will also be quite clear that

The studio, with seating accom the rapidity of this variation de through a suitable intermediate modation for a 1,000 audience, had pends entirely upon the difference amplifier, where they are modified a balcony which projected so far in frequency between the currents, and interfering signals are rejected into the actual "auditorium" that If there is no difference at all, then At the end of this we have a re-

9,020 FTL 8 A., Sat. 3 a.m. & 10 am..

Not regular 10.500 7.1.0.0.077 Bildnight daily 2.ME. PLE.

10,526 Not regular 11,020

Midnight-3 am daily

IRTUTE, 111030 pm, & 3 a.m. daily, except.

24.5 Manila

KIIR

23.06 Bobetiectady 18.88 Bandoeng

18.4

17.4

18.0

PLG. Kootwijk (Holland) POLUMA Bandoong Bangkok 16.& Kootwijk (Holland) FCK

Bandoengu

21.0

19.98 Pittsburg

the currents will never fall out of iatively rebo Lilocycle carrier, part of the orchestra would have 16.7%

tep. If the difference only and which, however, is again modulat been underneath the upper floor 16 ye it will take a relatively long time ed by the low frequencies ranging This, of course, could not be to before the currents become com from 0 to 5,000 cycles, correspond pletely out of afsp, and in fact the

lerated, as netual time period variation frem.

ing to the speech or music. The beat frequency, produced by the studio would be quit a maximum to zero and back to a first detector does not, affect the for broadcasting

such

12,840 Nightly

Saturday and Sunday

12,850 am. Wol, Fri. Bat. 10,10% Daily 6.80 pm to midnight

Delly 7.p.1.

10,804

$17.280

11.8.1.9.3 17,761 Sunday 17, to midnight

7 p.m. & midnight 18,404

Kich afternoon. PLENZA 19200 || 11⁄2ily 1,30–7 pm i

(UW.SIK, 111an Notrügule

suitable: coramafallowance must be made for 4'amou

The builders pean countries, which is one hour ahead of true time.]