HONG KONG DAILY PRESS, THURSDAY, AUGUST 21, 1930.-
MAKING A TEST
RADIO
FEATURES
INSTRUMENT.
A USEFUL APPLICATION OF OHM'S LAW.
The value of a measuring instru- ment as a means of detecting faults in a radio circuit was discussed in these columns a week or two ago, when it was pointed out that with
n' good meter and a few terminals quite a useful test instrument
could be constructed...
Many enthusiasts there undoubt
[BY COHERER."'"]
higher voltage of 200 or more ap plied to the anode of a power valve.
Adaptability of a Mater. With a good moving coil meter and some carefully designed home made resistances it is quite possible
for the enthusiast to construct an
will instrument that
compare
ends of a resistance, then it is obvious that a current will flow through that resistance, the current increasing with greater values of potential difference but being amal as the value of the resistance .increases. This fact is, in effect Ohm's Law, a better expression being that the current in amps is
QUERY CORNER.
V.N.A. There is little to choose between the two sketches of aerial systems which you have submitted. Both are good. Greater selectivity would no doubt result from shorter Rerial. As requested, a further article on the aerial will be published in the near future.
A resistance of about 30,000 ohms
NEW THEORIES OF THE ETHER.
his
HEAVISIDE LAYER IN
DOUBT.
which is believed to reflect wireless waves back to the earth again, Red so
facilitate their journey round the globe.
Still Impenetrable. Although it was not regarded as completely satisfactory, the Heavi
side theory has rarely been serious
When Dr. Einstein propoundedly disputed. Now, however," Dr. new theory of space at the A. S. Eve, who is Director of the SOME USEFUL HINTS.
World-Power Conference in Bor Department of Physics at McGill University, Montreal, and is also "Motor-boating," a rather com
President of the Royal Society of. mon form of L.F. oscillation, canlin recently, and declared that we
'anti-must abandon the present hypo- Canada, comes forward to challenge be cured in most cases by an mobo" stopper. This consists of thesis of the ether, radio engineers the entire hypothesis. in series with the ransformer began to consider the bearings of primary of the anode resistance, this dictums on the many unsolved and a 2-microfarad condenser con- problems of wireless transmission. The "Einstein conclusion, how nected between this junction point. and earth.
ever, is by no means new. Pre-
reached some time ago by the late of wire, air spacing, and so on Dr. Steinmetz, the famous determine the wave-length range thority on electronomics. He con- over which the choke will work properly. Some chokes fail below tended that the ether wave theory about 150 metres, but work well was merely a form of word, de- up to the extreme wave-length
The Heaviside layer is an electri- cal conductor which surrounds the earth at a distance which varies. between 250 to 400 miles, according to the time. Beneath it are two others, also electrical conductors, which form belts, respectively, 150
earth's surface."
edly are who prefer to become £10 or more, designed to cover the volts divided by the reaistance in be chosen for the circuit in which cisely the same conclusion was miles and 70, miles from the
familiar with their set without wait ing for a breakdown, and to be able to measure the various volt- ages and currents in a receiver is
of the greatest assistance in this respect. With such a means it is possible to check the characteristics of valves, of great importance in these days of super-tubes, the A.C. resistance, amplification filment and anode consumption need no longer be, a matter. of guess-work.
factor,
To obtain these and other mea-
surements a fairly considerable range of meters would be necessary in covering all currents, from the one or two milliamps in an anode circuit to the heavier current of half an amp or so in a filament cir- A similar range is required cuit. for voltage measurement, it being just as necessary to have an accur ate reading of low tension in the order of 2 to 0 volta as for the
The
"
favourably with a test set costing equal to the potential difference in
whole range of readings that are Ohms. The law is usually stated of importance in a radio receiver. as an equation IV/R where I is It has been the aim throughout the current in amps, V the poten these articles to avoid technicalitial difference in volts and R. the ties as far as possible, but with the resistance in ohms.. present subject it is necessary to give some consideration to Ohm's Law. No doubt the majority of readers who are sufficiently inter- ested in their bobby to contemplate constructing a test set bave already some knowledge of this important bearing on electricity, which ex-
presses the relationship between voltage, current and resistance in a DC. circuit. As it will be peces- sary to refer to this law step by step throughout the present article, a brief outline of its possibilities and applications will undoubtedly
be of assistance to many,
Ohm's Law,
If a steady difference of poten- tial (voltage) be applied to the
EVERYTHING.E.C.) ELECTRICAL
your guaranter
TENACIOUS COATING
KEEPS YOUR SET
AT PEAK PERFORMANCE
It's not the filament but the coating on it that
MADE IN ENGLAND
Sold by all Wireless, Dealers.
counts
Osram
Valve
Osram Valves
with the TENACIOUS COATING
WRITE for !! OSRAM WIRELESS GUIDE (1929 Edition) Sent Port Fren
High frequency chokes have to they will be used, and the amount
21-
Since the equation is an expresimit, whereas others go down to signed to enable scientists to find sion of the relationship between about 20 metres, but fail above their way out of a difficulty. three things, it is apparent that 1,000 metres. he value of any one can be obtain ed providing the other two are known thus:-
1
(a) to find voltage when I and R
are known-V=I x R.
(b) to and resistance when V and
I are known-R-V/I.
(c) to find current when V and R
are angwn-I-VIR. Providing, we strictly adhere to the units, volts, nips and ohms and do not stray into megohms (one million ohms) or milliamps (one thousandth part) we now have sound basis for calculating the requirements for adapting a meter to a number of uses, taking the three equations expressed above as our main support.
Qonverting a Milkameter..
As an example we will assume that, the meter" obtained is a mil Hameter giving a scale reading up to 50 milliamps, and having an internal resistance of 50 ohms... The voltage flowing across the instru ment when its maximum scale read. ing of 50 milliamps is registered can be obtained from equation (a), R in this case being 50 and I (com verting to amps) being .05. Refer- ring again to equation (4), it is seen that voltage is the product of current and resistance, and there- fore a full reading of the meter will indicate 2 volts (50 x .05). The instrument then can already be used as a voltmeter, a scale rend- ing, of 50 indicating 2 volts and so' rn, pro rate, right down the scale, each
volì giving a needle deflec- tion of 10 milliamps.
The main difficulty so far is that we are able to take readings of low
voltages only, a greater voltage in all probability rendering necessary a new instrument. In fact, a single accumulator cell having a voltage of little over 2 and voltages below this being of no consequence in radio, our instrument as it standa may be regarded as useless as ta voltmeter,
Extending the Bange.
Never hang your 'phones near ar accumulator, as the gassing and fumes are capable of causing injury to the delicate windings.
The voltage of an accumulator should never be allowed to drop
below 1.8 in, the care of a 2-volter; 3.6 in the case of a 4-volt; or 5:4 for a 6 volt accumulator.
Accumulators should always be
kept in cool and dry place (not easy to find in Hong Kong).
The aerial being outside, it is liable to be forgotten, and both electrically and mechanically it is gang agley." It would liable to Fay to overhaul the whole equip ment before the winter sets in.
፡፡
The difficulty in obtaining ampooth reaction control in a short wave set can often be overcome by means
He preferred to regard the so- called ether waves as merely the
manifestations of the alternating electro-magnetic field of force which We extends through all space. are, in fact, precisely where we were before Dr. Einstein deliver ed his address.
When the electro-magnetic field is distured by radiations from a transmitting wire it causes vibra- tions which affect tho receiving. aerial, and the receiver translates them back to the music or speech which first produced them.
There is another recent phase of radio research, which opens up what may prove to be a much more fruitful field of inquiry."
Wireless students are all fami- of a potentiometer, the ends of liar with the theory of the Heavi- which are across the filament, the slider being connected to the grid raide layer, that apparently simpene trable belt of the upper atmosphere leak.
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 mode- rately good get suitable for ré-- ceiving such signals. Success in picking up these stations also dependa very largely upon fay Durable atmospheric conditions. Readers are invited to add to this list should they succeed in picking up any station not in cluded in either of these lista.
LONG-WAVE STATIONS.
Wave length
Call Kilo- (Metres) Station Sign cycle
980 Manila K.Z.İ.B. 1,133 277 Shanghai ES.M.S. 1,085 280 Tientsin.C.EC. 1,070 310 Shanghai ER.C. 967 320 Peping
G.O;P.K £5
345 Tokyo J.O.A.K. 870 353 Hiroshima J.O.F.E 630 355 Hong Kong Z.E.W. 646 357 Bombay V.U.B.. 840 281 Sapporo
J.O.I.K. 830 306 Keijo
370 Nagoya 370.4 Calcutta
J.O.D.E. 820
J.O.C.K. 810 .V.U.C
380 Kumamoto J.O.G.K.
390 Bendai 395 Dairen 398 Rangoon 400 Osaka 410 Canton " 413 Manila
SHORT-WAVE STATIONS.
STATION
CALL SIGN
67.85 Dabintz (Germany) 60,19 Khabarovsk (Bussis) 68.7 Nauen
The obvious plan is to arrange
43,5 for the voltage to be dropped be-
· 42, fore it reaches the delicate wind- 413 28.3 ings of the instrument. The de
BT. gree of drop being known (R), it is
32.4
10.
Moscow
Pome
Perth Singapore Hootwijk (Holland) Bangkok (Bism)
elbourne. 81.55 31.48 Schenectady
A.FE, B.ADY- A.G.J. BENE IMA 8.4.0.1
V.6.1.4.B.
KILA
CYCLES:
800.9
790 J.O.H.K. 770 J.D.A.K. 780 V.U.K. 754- J.O.B.K. 750 CIM.B. 732
·K.Z.B.M;" 726
Tuex (Hora Kora)
02 WORKING"
4,434 Bion, Wod. 4 Fri, 6 pm, & à am.. 4,990 || 6–10 pm.";
6291(Not regular
5,000 To Thurs., Sat., 8 p.m.
6896 Bunday midnight
7,142 Dalir 8.30 p.m. & 11 p.m.
7,810 Not regulat
1,780
Daily 11 pm.
F.C.L HSLPJ 2.BL. 810. WALLF. 9,680) Dally 74-mu
8,106 Tues, & Fri. 9 pm-1am
9.230 Not regular.
a matter of simple arithmetic to again revise our scale reading. Let 31.20 Eindhoven (Holland) PC.. us assume that we wish to convert 81.23 Sydney
30
81 Nairobi
(Kenya)
27.5
9,500 Not regalar
0,020
Bat, 8 am, & 10 azn.
2.7.0.
5.500 Not
7.LO
9,677 Midnight daily
2.M.E.
10,526 Net regulag
11,020 Midnight.. daily
Sydney
P.LB. Bandoong 26.53 Chelmsford (England) 5.5.W,
24.5 Manila
23.35 Schenectady
18,88 Bandoeng
184 Kootwijk (Holland),
17.4 Bandoeng.
18.9 Bangkok
an instrument to a voltmeter giving 28.5 a maximum reading of 50 volts, each milliamp division on the scale indicating one vok. It is merely necessary to calculate what resist ance must be applied to 50 volts. to provide a current of 5 milliamps, This is obtained from equation (b), K-being divided by I, - divided by 05=1,000. The resist auce of the meter must be taken fiata acement which denne ar
stice of 950 ohms to be wired in, series with the instrument to make it a voltmeter of a very useful sizë. The further application of this prin- ciple, with notes on the construc- tion of the adjustable resistances, will be dealt with in a later article.
16.88 Huizen (Holland) Jan Rost if's folland 16.7453 lo 14.6
Nasor (France)
19.30 Pittsburg
11,781 7.80 p.m. & 8 am, daily, except
Saturday and Sunday
A: Wed, Fri, Sat. FL.G. 16,102 Daily 0:30 pm to midnight
KLIK.
12.240 Nightly
W.3.X.O.
12,850 4A
'
P.C.L
P.LF. H.6.LE.J. ZHL
10,304 Dally pa
17-280. Daily 8 p.m. to midnight
17,761 Sundays 7 pane & midnight-
17,769 Drily
10 pm:
18 4041 Each stre
10
19361 Dally a
WBIK
21,540 Not rögül
[Allowance must be made for summer-time pean countries, which in one hour ahead of trus time.]
mort
Professor Eye's theory is that, sa'! the wireless waves cannot penetrate. a conductor but are reflected by it as an image is reflected from a
mirror, the theory that they reach the 400 mile layer must be aband oned in favour of the hypothesis. that they are reflected in a series of zig-zags from the seventy mile layer to the earth and back again from the earth to the seventy mile layer and so on:
If Dr. Eve's theory should be confirmed, it means good-bye to any hope of communicating with Mars by wireless. It also means the re consideration of many points in connection with long-distance com- munications by radio along. "the earth's curvature.
T. C. C.
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2. 1
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BANK OF CANTON BUILDING,
TEL 24405.
A RADIO
THE
LOEWE
FE 63
9 tube set.
A new shipment, just arrived, is one of the most sensitive. instruments for long distance and reception with six stages of high frequency.
This set is fitted with new Barium tubes and requires a Frame Aerial only. Can also be used with LOEWE short ware attachment.
Just arrived-New Shipment of LOEWE R533 A.C. SETS.
8126 without Loud Speaker, 8150 with Loud Speaker Newly arrived
Loud Speakers of various types. Pertrix Batteries 150, 100
Gramophone pick ups of best.
Gramophone Electric Motors
and Gid Biss Batteries,,
quality,
BEliminators a speciality to fit any requiremiant
Demonstration Hours
11-11.30 am. 12.30–1.30 p.m. 5–5,30 p.m.
During demonstration hours expert Eusópran advice is giren on all Wireless matters.
THE
ICANTON TRADING ASSOCIATION—— LTD. CARL SCHROTER, Manager.
5TH FLOOR, CHIEL BLDG.
TELEPHONE - 24610′′