1971-08-18 — Page 15

RARY

18 ADC

育教係食三纩張四第F八廿月六年亥辛屣OWAH KIU YAT PO

報日橋T

CITY

育教僑華

IEME 中學同學暑期進修專欄 臺道英文書院主碼

畢業同學

暑期進修專欄

智慧出版社主繻

無綫電入門(五)

THE RADIO COMMUNICATION SYSTEM

Audio waves travel only a short distance but ar radio frequency carrier can travel long distances. In order to send the a-f signal to remote laces.

ceminaled into a re

三期星

RECETVER

日八十月八年一七九一零公布十六國能太

There are many r-f in the air.

Ferent frequencies, each carrying its own signal.

The following block diagram shows how a particue Tar sighár is selected and turns to

wave.

新數量(九)

Elementary Modern Mathematics

MODULATOR INFUT

OUTPUT

R-F INFUR

M

Mu

Problem

eg.

Lesson

Numbers

on the number line

ltiplying two negetive numbers:

(-2) X

When multiplying two negetive number.g we have to be very careful in deciding the direction we count.

Steps

Steps:

Thus

T)Find: -2 by counting 2. unite

to the left

-3 means add for 3 times in the opposite direction from e

3) The point we arrived at is the g

answer;

UNITS.

1+2+3+4

+7+8

arriving

Count 3 units to the left

-3:

-4 means adding four times the value of negetive 3. In the opPON site direction/

The point we arrived at is the aaswer

+2

+6 48

10 12

Thus, (-3) x (-4)

From these two examples, we can see that multiplying two negetive numbers

WE

shall get a positive number

Division on a number lina

What is division ?

Multiplying,38

Dividing 12 by

we get 12

we get

Multiplying 6 to 5

we get 30

Dividing 30 by

we ge

tion,

Here, Just like subtraction which can be treated the opposite operation of addi-

advision can now be treated as the opposite operation of multiplication. There- fore, it can also be solved by using the

umber line.

Froblem

Dividing 12

Steps

1) Think

What number multiplytoy.

3 gives 12 "

(2). Count, 3 units a time,starting

from zero.

G

Count up to 12 remembering

how many times we have counted " The number of times we have coun-

ted will be the solution. This is equivalent to " How many times we have added 3 to get 12:

Other problems can be solved in the Similar ways mentioned in previous lessons.

J'UNITS

menge. : 12

E

unis is a block diagram of a modulator unit showing the a-f and r-f input waves and the modulated r-f, output wave, The principal

tionof the modulator to carry the a-f onto the r-f carrier.

The art and ruf waves are combined in the modulato of a roadcast transmitter, and the moāulated wave is radiated by the transmitter antenna ro remote

zaces,

This

The pr

block diagram of

broadcast transmitter ripal parts of this radio transmitte

Microphone

Audio frequency Amplifier

Oscillator

Modulator

cenne

Audio sigma ( spund:

~

energy) is transformed the microphone to shell or weak electrical energy

ich is then lified by the 4-5 amplifie

(2) to a stronger signul. ((3), a local oscilla por. It produces a radio frequency with constant em- plitude. This is the carrier wäre which

to carry its passenger, audio-frequency to a re- mote place. The a-f signal mounts on its carrier wave in (4), thy modulator. The modulated wave, as then seut by means of the antema to the sky.

一優異,出入党張 「無考畫業爭绝, 識之

有風景,有阿案,有說 有靜物,有人物:

·如許多同行的朋友一 嗚,以他們國健· 朗的心靈,某他們共

一撕水彩,油冚慢用美 他們對作的一百餘 校畢業出來的车,以 千七位剛從香港美乐器,

伊芙敬·對戒·持类 鍾志那張仙·龍國

《驚影,黃寶龍,馬榮超 陳中栖:澳東,徐

七人聯合發展」,省

The

5

The principal parts of a radio receiver area

1. Antenna

Taner

Radio-frequency (r-f) amplifiery

„Detector

Audio-frequency (a−2) amplifies

Aeriker.

travel from an erinas of broads

cast fransmitters to an antenna of a receiver

through

If a program broadcast on 810

ke de Space the timer of the receive:

-

be tuned to a resonant frequency of 610 kc. In this condition, the antenna and its tuner provide

Sasy path for

the

810-ke signal to pass onto

.

the next stage, the r-f amplifier (3). The weak,

carrier is amplified here and is passed to ithd detector stage (4) - The detector "separates J-e and r-f waves. It rectifies the amplified {-} devrier and filters the r-f portion, The remaining e-F portion is fed to the a-f ampli- sier (5). A low Frequency, amplified electrical arargy 's. changed to soun energy bv a device: known as loudspeaker le

The receiver system discurbed in the previous paragraph is TFF (tuned radio froquercy) set.} There are many disadvantages in. TRF sets. The Ciffiquity of proper tuniky, the poor Stability, together, vith many other disadvantges lead to The invention of the "perheterodyne" set. Advantages of the Superheterodine systeens

prod

alu signals receive the same uiount of amp13 Catim), Gain is substantially in legendent of signa frequency,

Bandwith is substantially constart. A11 så signals are amplified by the same fixed-punet amplifien.

3. Excellent elabhly, simaïs are amplified at three different Frequencies, radio frequenc intermediate frequencies, and finally, audio frequencies. Thus, there is little chance of Oscillation if the outpu -f the final stages should find its way la to the early stages.

·被后·從夏宫说肉整等做時,藉一次两人包围。一合樂國際社照片)

「十七人書展」觀後談 -

滿青春氣息的書展

息

我能不出的快。王新潮. 喪一監得堅果香風、有」 山田本水、水肜) 陳摶作 人事行的「十七人脈會素 仙,陳中辐等人物的人一直達,無論必然再有女 ,看了在大會堂八核1 李佛 黃龍媵]物案描,或油盡·形象 一本月

韓藝術節教師奏新

在紐約中央公E表團共

在街上向一小孩子祝闢 鮈1名小學辦。(下圖)

教宗主持聖母升天後宗保綠水世主

華

僑

青年豪家,攒性國狂一來陳海道、黄湖究的心 日用食品,而少花草, 得他們的校長,做低聲,楊畫取材於工作工具、機拨基生硬盤賽吧! 成之嵒諫,用色豐富、實用美術,也有神,使君安系界得可 可 無不突出人物神花、果實長中的靜物業及接著,攜式主莊午粱 :老功离工人,美,用实可算成黏:效果。他们的双手慢 说我們明年烟再

討

鄭慶龍近作 今天仍展出

設

行同時來

「榮商舞人士,黨効果虯類雲機會。忘花園道识的餘供堂一行。

·自是照明雜志之士小射枝粉,龍無限期已第三天-今低薪铁一 從齒律,能扶君子之花,亭亭獨立之念。「艾福貓之人物,高士扶筇,見他們在街頭巷,郊一夏祖與稱許。生們上一 阿正文土產,產開時 (工之美。, 劉氏出生之地,今多多實此當氣,是亦不忘本之意。「基而一些一顆徵,周宋假期,一直為社會人士所 紅毛丹一戰幀:善馬來 海梅欣賞,艾別其墨染,齒質黨接、書魔慣羅。水山為國谿徑,講正官真,外孫氏為生。這大一十座熱度的千人 消息刊在

·香港 七人嚙合書展」中風 廣

而進實人士,仍无洛镰不」的難阿,說明杳洒碗專用美術設計,有他們自 成就,秭熱飲福。馮中EL和成功的。一來,餘類色裡有平,發哥更多,展拙复的創 視,有打規,對影氏之一的基礎教臂品十分健中心 乙的第二大量間,從中 主的基成

.作吧L

者二第消尙

四息有

意請張刊文

讀第在化

「竹石同無間」郭慶龍作品(马要出花馬聖約翰強)

生

形成辦一

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