1931-06-18 — Page 2

HONG KONG DAILY PRESS, THURSDAY, JUNE 18, 1931.

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TADIO

FEATURES

POWER GRID DETECTION.

A DEVELOPMENT FOR THE MUSIC LOVER:

If you want Best British the highest possible moving and so leads to a serious loss in to zero for all frequencies below feception from land stations, in lations

Components, it is undoubtedly

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the upper register. They forget that a by-pass condenser in the plate circuit of the anode bend rectifier can be equally at fault in this respect,"

touch with their ships in any part that may be required later. As. of the world, Consequently the-an-illustration of this, it may be power, wavelengths and range of pointed out that during the last transmitters now in general use are two years progress in wireless telo, such that communication in day phony has been so great, that in light can be carried on over dis ddition to their wireless telegraph tatrices of overal hundreds of equipment some ships are miles in many cases over 1,000 equipped with short-wave wireless miles. The use of valve receivors telephone installations by which gives a correspondingly long rango conversations can be exchanged of reception from other ships, and, ovor practically a world-wide of course, a much greater range of range. In each case these instal

havo necessitated cluding almost world-wide recep- arrangement of existing accomoda- tion from the Rugby station of tion and the provision of oddie the British Post Office..

tional accommodation. For short The leak resistance instead of these days,

.80 rapid wave telephony the transmitting being 2 or 4 megohms as usual, is

been the development of and receiving houses must be in reduced to 25 megohms... This

wireless, there

Д very different parts of the ship, and in allows the grid. condenser to dis

wide range of apparatus,from addition telephone office has to charge in a very short period of which shipowners can choose. The be provided for the use of pas time, e in less than one ten installations embody main transsengers. It has been found desir thousandth part of a second, 80 mitters of varying typos na poable on other ships to instal dup that the highest essential musical wers, receivers, emergency installex high-speed telegraph services in frequency can pass through with lations, lifeboat sets, and such order to receive Stock Exchange out causing the grid to "choke" auxiliary equipment, as Direction quotations for their brokerage and so produce frequency" die Finders, Auto Alarms, her wave service. This again means increas tortion. The higher plate voltage transmitters and receivers, and d accommodation. is also found to eliminate ampli-wireless telephono equipment for tudo" distortion for any denth of

all classes of ships. modulation, up to 80 per cent.

Put in another way, power grid:

The modern receiving set is now the grid-leak and condenser. Its grid condenser and leak than be falling into two distinct classes, supporters point out, quite rightly, fore. By lowering the capacity of one suitable for general purposes, that the grid condenser offers a the condenser from 00003 to 00001 and the other specially designed to shunt path to the high frequencies mfd., high-frequency loss is reduced coil quality at comparatively close

10,000 cycles, which is the highest range and with great volume.

practical limit of audibility" The new method of power grid rectification represents the latest advance towards perfect, ie, dis tortionless reproduction. In spite It is also true that the grid-leak of its growing popularity and of rectifier produces serious distortion its use in many of the mains-driven on high input voltages. On the sets-the difference between power other hand, it will respond to in grid-rectification and its older put voltages too feeble to bo detect rivals, "lenky grid" and "anode ed by an anode-bend rectifier, Le bend is not widely understood. it is more sensitive than the

The earliest valve detector was latter." the two-electrode valve, which, "al- Increase in Impedance. though theoretically perfect so far

Again the grid-leak circuit allows as quality is concerned, did not grid current to flow. It therefore long survive the appearance of the tends to "damp" the turned cir

has

The Wireless Cabin.

Interesting confirmation of this point of view is to be found in the wireless accommodation of the "Bremer." According to a writer.

leaky-grid three-electrode detector.cuit of the preceding H.F.. stage detection consists in adjusting the for a wireless cabin is now impos.in the Journal of Commerce, her

detector valve so that it operates on the straight-line part, both of the plate-current grid-volts curve and

internal impedance of the valve, of the grid-current grid-volta eurve.desires to be made of the Wireless ship'a crganisation, and its im

An Interesting Comparison. and so reduces solectivity. Aa Volumes have been written on the against this, anode-bend rectifica. precise action of the grid-leak. in tion necessitates the use of a large separating-out or detecting the negative bias, which increases the signal components from the re- ceived carrier-wave. So far as the and makes it essential to use high- resistance coupling to the first L.F, purpose of this article is concern. ed, it is suficient to say that recti-amplifier, with a corresponding in-

crease in H.T. voltage. fication here takes place in the grid eircuit

By contrast, in the anode-bend. detector, the signals are separated out from the high-frequency com-

Inconclusive Arguments. · In short, arguments on the re- lative merits of grid-lenk and anode bend rectification appear to

It is obvious that a standard size Bible, and the choice of wireless installation is not limited to accommodation for a ship must de wireless cabin. It has been raised to 4 definite department in the pond upon the use the shipcwnor

Grid Current is Necessary.

Station. The remarkable, progress made in the application of wireless As sone current must flow in the to shipping has emphasized., two, grid circuit (to ensure rectification) points in regards to acceminoda there should be no negative bias on

Firstly, it is to the the grid. In mains-driven valves, shipowners advantage to consult the grid may be connected directly the wireless companies in to the cathodo, but for other valves to new installations, and secuud accommodation should a small positive bias is necessary. ly, ample

tion.

portance has heen recognised by the allotment of liberal"accommo dation

The importance which the German shipowner at- taches to the equipment of a wire-, less department is forcibly ill ustrated by the accommodation provided. No fewer than twelvo spacious cabins have been set aside

ponents in the anode circuit of the be unending and inconclusive to far This, combined with 100 volts on be reserved, bearing in min ensure the efficient working of

valve.

This allows a very simple distinc tion to be made between the two methods. In the leaky grid detee tor the carrier-wave is first recti- fied (in the grid circuit) and the rectified siguals are then amplified between the grid and plate. In other words, the valve combines the task of reetification with one stage:

of low-frequency amplification.

In anode-bend rectification, on the other hand, they carrier-wave (including the signal components) is first amplified between the grid

as proving the superiority of one method over the other.

!

the plate, means that the total cur-espréially in the case of pussenger rent passing through the detector ships, the possibility of addite as this department.” valve may be of the order of 6-8 As the name implies, power grid. rectification is a reversion to the milliampe, instead of 1-2 milliamps. principle of grid-leak rectification, as usual. Hence the term "power"!. but it is combined with certain im-grid-detection. provoments which remove its origin- al defects whilst incorporating the advantages of anode-bend rectifien- tion,

Not for Dry H.T. Batteries,

Such a

would, output current

be a serious drain From one point of view it is on a dry-cell H.T. battery, though development which has been made it is immaterial in the case of possible by the use of H.T. mains mains-driven valves. If the recti- units. One hundred voite on the fer is transformer-coupled to the plate, particularly when used in

first L.F. stage, a parallel-fend conjunction with resistance coup-should be used to prevent, satyra-

heavy D., component.

and plate, and the low-frequency fing, rules out the use of dry-cell tion of the transformer care by the signals are afterwards. separated T. batterien unless 200-250 volls are available, in order to com- pensate for the voltage drop across the anode resistance."

from the high-frequency components in the plate circuit. That is to say, the anode-bend rectifier is equivalent to one stage of E.F. am- plification, followed by a stage of detection.

Anode-bend rectification claims to be an improvement on the use

MARINE WIRELESS

INTELLIGENCE.

CHOICE AND SIZE OF INSTALLATIONS,

The low value of leak resistance. used naturally tends to damp the preceding stage of H.F. amplifica Where the Difference Lies.

tion, but since the main object of With the high plate voltage of power grid-detection is purity of 100 (as compared with 40-60 on an reproduction, any loss of selectivity ordinary leaky grid rectifier) is due to this cause is of no practical combined the use of a much smaller importance.

The introduction of wireless tele graphy to the mercantile matine for

..

HAVE YOU HEARD THESE? DAY

SHOR

LONG-WAVE STATIONS.

WAVE length

| (Metres) Station 200 Manila 277Shanghai

345 Tokyo

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 set suitable for re ceiving such signals. Success in picking up these stations also depends very largely upon ourable atmospheric conditions. Readers are: Invited thy add to cabasan Keijon this list should they succeed. in....

370 Nagoya picking up any station not in- „ cluded in either of these lists.

Lav-

Call Kilo-

Sign cycle

KZI.B. 1,153,

K.S.MIS. 1,083

J,0.AK 870

353 Hiroshima JOFK. 880 355 Hong Kong Z.B. W. 840 #387.1 Bombay, VUB. 840 381 Sapporo J.O.L.K. 830

370.4 Calcutta

1.0.D.K. 820

3.0.0.K. 810

V.U.C. 809.9

380 Kumamoto" J.O.G.K... 780 |

330 Sendai 395 Dairen "400 "Osaka; *410 Canton 480 Manila

SHORT WAVE STATIONS.

J.O.H.K. 770

750

J.Q.A.K. 780 J.O.B.K. C.M.B. K.Z.R.M.

Tam (Hong Kona)

OF WORKING,

738

625

STATION

CALL BION

67.65 Doblutx (Germany)- (0.12 Khabarovsk (Rusia)

587 Nauen AG.1.

A.F.E. BA07,

4,494 Mon, Wed. & Fri.,: 0 p.m. & 2 a.m 4990010 pm,

5201 Not regular ---

more or less to 80,

1.MAJ

42,

$18

39.8

87.

321

31.55 Helbourne

Singapore Kootwijk (Holland) Bangkor (Blam) HS4PJ,

2.BL Sydney

3.1.0.

7.8.1.4.3.

B.C.L

81.48 Schenectady

W.2.X.A.F.

Extension of Range.

Bandourg

P.LR

0,000 Tuck Thin, Sat, 8p.m.

6,896 Bunday midnight

7,12

APLE DAIS.4.80 p.m. & 11 p.m. 7,810 Not regular

7/780 Baby 11 pm.

8.108 Tues. &

0.230 Net regular

0,503 Not regular."

8,680 Daily 7 Bm

11,030 Midnight3 m. dally

7.30p.m. & 3.m. dally, except

11,751, 720

during transmission and conse-modation was built with the ship, quently disturbing to occupants cf but was adjacent accommodation. Often a standard bize as in those days, top the chins were below the top there was very little choice of ap deck and aerial insulation difficul, paratus. tics presented themselves, redue- ing the elfeiency of the set. An-

With the introduction of legis

8120 Eindhoven (Holland) PCJ 0020 Fr. 8 mm. Sat. 8. & 10. other important item was that of

$1,28 Sydney

EF.C. 0.00 Not regular Nairobi (Kenya),M.5.10,520 Not regalar

0077 Midnight daily 91, revenue as andemmodation, taken lation and the compulsory equip. ment of ships with wireless appará-

28.6- Sydney apparatus would wireless

"tus, regulations were brought into 273. was immediato,y recognised as a normally be occupied by fare pay force, embodying, minimum stand 26.68 Chelmsford (England) B.E.W. matter of

arils for apparatus and accom-245 "great importance to ing passengerspreid cont d that industry and was soon follow- As recognition of the value inodation. The regulation regard. 28.35 Bobenectady

18,68 Bandeng ZE ed by domands-from shipowners of the now science increasing range and wavelength of trans 1.

18. Kootwijk (Holland) 17.4 Bandoeng for installations on passenger ed, special cabins wore added mitters can be techuically, ohsarved

Bangkok ships. One of the

Kootwijk (Holland). the first questions to ships to house the apparatus and, by installings, spark transmitter 16.3

15.74 Bandoung to be considered was that of ac usually, the telegraphists as well, of low power operated from a bat

Nansy (France) commodation both for the ap but theko: cabins were necessarily tery of accumulators which are

18.03 Pittsburg paratus, and operater and in the emal owing to the limitation of charged from the ship's mains majority of casos existing cabins apnoeana ship ready, in om- Shipowers have found, however, had to be used. These were not al- mission. On ships under constructat 10 is to their advantage jun ways in deal, positions, bronuse tion where hrrangements were instal níore useful apparatus, giv- w the early ann

mado te instel wireless the accom ing them the means of keeping in

10.0

16.5

Manila

KLXIA 12,240 W.2.X.O.

240 Nightlyday and Sunday 12,850m Wed, Fri, Sat. P10,304 Dally p

-16,102 | Daily.6.20 p.m. to midnight :

P.C.L. LF.

P.LF.

17.290 Daily 8 pm to midnight

H.5.1.P.J,- 17,761 | Sundays 7 p.m. & midnight P.C.K

| 18,404 |: Bach afternoon);

P.LE.

W.8.X.X.

{Allowance" must be mad which is on

19,220 | Daily .80 -7 pm)

| 19,351.) Dally 8, am.

| 21,540 | Not regular

sunmer-time "-in-mos

gend of trus time