TO-DAY'S WIRELESS
PROGRAMME.
BROADCAST BY Z.B.W. ON
355 METRES.
13 to 11:30 am-Stock quotations. 1:30 am-Chiness programme, 19.30 p.m.-Europena programme. 1 p.m. Local time and weather
report.
1.30 pm-Rugby Pross news, mail
notice, etc.
- 9-p.m.-Close"down.
4 to 8p.m-European programme of Columbia records supplied by Messrs, Anderson Music Co..
8 to 0.27 p.Bis
Orchestral and Band Selections." "Old Folks at Home and Abroad. ***
(C. J. Roberts)-Reg. Band of H.M Grenadier Guards, DX230.
HONG KONG DAILY PRESS, THURSDAY, SEPTEMBER 10, 1931.
RADIO
"WIRELESS PATENTS.
PUSH-PULL AMPLIFICATION,
which In any industry in the question of patienta has presented a bigger problem than in wireless From the very bes ginning of broadcasting, the air has been thick with mutterings of royalties for this; that, and the other type of valve or circuit, and battles "royal are continually being fought in the courts to decide the ownership of the spoils, I suppose it is inevitable that these things should be. Certainty the inventor, like any other worker, is worthy of his hire. But it is all rather confusing, and difficult for the or dinary layman to know how and
where he stunds: --
One of the most important of the various patents still in force is that covering push-pull amplification. This was granted on January 7, A Village Romeo and Juliet" 1915, to Western Electric Co., Ltd.): Delius), Sir Thomas Beecham and so was, in the ordinary way, and the Royal Philharmonic be due to expire on January Orchestra.-L.2087.,
1031, after enjoying the full normal Bronwen"-Overture (Holbrooke) "life" of sixteen yearn. How -Symphony Orchestra, conductor, the High Court has grant od by Claud Powell-LX. ed the present owners
6.27 to 6.30 p.m.
Scottish Selections,
Humorous Song-"Sailing.
an
tension of four more years, on the ground that the intervention of the War hindered the full develop Upment of the patent and prevented the inventor, from reaping his just reward. So for this further period
the Clyde"! Humorous Song-"Ye Can Come
and Be the Baby."-Will Fyffe .--9408. Chorus "On the Banks of Allan Water" (Lewes, arr. Cantor).- Excelsior Male Voice Quartette, -GA770.
Vocal gems-Sir Harry Tauder's Songs." The Border Singers
with Orch. DX110.
p.m.-Stock quotations and mail
notice,
4.80 to 8 p.m.
A Concert. ... 'Cello Solos Sarabando " (Sui zer)-Ave Verum." (Mozart). -W., Squire.-12260 Song O Lovely Night" (Tea chemacher and Sir L. Ronald). Danie Clara Butt (Coutralto) PXL
amplification must continue to pay tribute as heretoforo...
a
In the High Court.
In the ordinary way it is not an
FEATURES
THE RETURN OF THE WIRELESS NET FOR POWER DETECTION.
SUPER-HET
CRIMINALS.
A FEW REASONS FOR ITS EXPERIMENTS TO LINK UP
ALL POLICE STATIONS.
POPULARITY,
All the signs and portents in dicate the early return of the super-heterodyne set. Phoenix-like, this system secs about to rise again, to even greater heights of popularity than it experienced several years ago. What is the super-het: why did it dio; and why has it come to life again?
Firstly what is the super-het 1 It invented to provide stable and ap. is aystem of reception originally preciable high-frequency amplifica tion; invented in the days when real high-frequency amplification on broadcast wavelengths below 1,000 metres "was problematical, if not. impossible.
attempt to make them amplify at Valves were so inefficient that'any high frequency was almost futile due to feed-back oscillation and negligible amplification factors. These valves could be made to give & moderate amount of high-fre tuned to a long wavelength, say quency gain if the coupling were 2,000 metres. A three-stage empli- fier with long-wave or aperiodic couplers, would, even with the mediocre valves of those days, give..
de tection-but only on the long ways- lengths.
London August 12.-Experiments are still being made concerning the scheme adopted by a conference of polico phief constables in 1930 for a nation-wide, "wireless net for criminals
Various provincial police forces arousing wireless as an aid to combating local crime but so far no definite plan has been devised by of the country can be linked to which the police wireless stations Rother. And no serious step has been taken towards establishing central broadcasting station for the
of the police...
AND COST.
A FEW TIPS FOR CONSTRUCTORS.
high tension must be
Those who use dry batteries for be careful not to proceed too far with power deter tion
There are two chief reasons, the current passed by the valve may first being that the fairly heavy| make the total load upon the bat- tory, excessive, and the second rea- son has to do with the affect of the the heavy current upon. of, say, 10,000 ohms in the deteo transformer, upon the coupling for example, you fit a valvo for position and apply voltage of 120, the current is, likely to be of the order of 8 milliamperes With 75 volts the current will ba about 4 milliampers. Now the vided for the setting up of three current passing through the primary The scheme approved in 1930 pro-be perfectly satisfactory when the performance of a transformer may
in wireless stations for the in-winding is 4 milliamperes, but is terchange of information concern likely to be poor when the current criminals and the distribution of ing crime and the movements of is twice as great. this information to substations and divisional offices. The main stations
Three Main Stations.
would be at
*
(1) Scotland Yard';
(9) Midland, probably Birming
ham;
Actual burn out is not to be fear- ed, but the inductive value may be reduced by the action of the cur rent to so low a figure that the performance is poor. The nature of the whole amplification frequency curve may, as a matter of fact, be, (3) North, Glasgow or Edin-changed by the excessive node cur-
burgh.
rent. No definite progress appears to have been made with this part of the scheme. Ohe explanation is to be unsuitable as a central atation that Scotland Yard has been found for the transmission and reception attributed to the following tausea of wireless messages. This can be
The close proximity of the Yard to the powerful wireless atation at the Admiralty.
The clore situation to Savoy Hill, and
A Mains Aerial,
sometimes, to be obtained by using The fact that good results are the mains as an aerial will, no doubt, be the reason for experi ments in this direction being carried cut by amateuṛs...............
A fixed condenser having good. insulation for the purpose, is con "nected between the aerial, coil of the set to one side of the maina When the set is of the mains' type, The large amount of the inter- the connection is made between the ference caused by the "Embank-coil and input from the mains to ment framears.
the set,
How the Super-hot. Works. easy matter to extend the life of with this system the long wave So the super het enme along patent. Part of the bargain made maplifier was tuned to maximum that the benefit of his invention wavelength. The incoming signals, by the State with the patentep is efficiency at one particular long must pass freely to the public at the end of the full term of sixteen of all wavelengths, including those between 200 and 600 metres, were years, unless the inventor can pro first received on a detector valve, in the High Court that he has passed through the long-wave am- prolongation. If he does so, itinally amplified by the usual low- reasonable grounds for asking for a plifier to a second detector and open to anyone interested to op frequency methods, poss the application. In the "prel sent instance, several well-known manufacturers, including the Colum Piano Solos Rondo in E Flat Mullard Radio Valve Co., Ltd. For the oscillations of this valve play an even larger part in the de- with the power plug connected in
bia Graphophone Co., Ltd., and the Major (Hummel) Viennese joined forces to argue that the Danco (Gaertner)-Ignaz Fried- man,£1730,
patent should lapse. But the Song-Love What Has. Given Court held that the full com You This Magin Pow' (ehar) mercial exploitation of the push Song Apple Blossoms (Lahar) pull amplifier had been held up by Richard Tauber (Tenor) four years by way of compensation. the War, and allowed the extra
Violin Solo-"Tambourin, Chi-The decision is one of considerable nois" (Kreisler) Menuet: (De interest, because in the long run, of course, it is the public who Bar-Duchkin)-Joseph Szigeti.'
R20112.
ven
phys.
-L2037. Vocal Dust Friendship (P
Sydney and T. Marvinla), Vocal Duct-"The Keys of Hea
Song Patiently Smiling (Traditional). Dame (Lebar), — Richardy.. Tauber: Clara Butt and Kennerley Run- (Tenor).R20107. ford.-7300/
8. p.m.-Local time and weather 'Collo. Solos-"Rigaudon (Tro- report.
well) Lament (d'Har veloise 8.05 to 10.30 pm. Chiness Squire)W, H. Squire,-2158. Song You Are My Heart's
Delight" (Lahar) (Continued on next Column.)
Silver
Marshall
-All Electric
gramme.
. Coupled to the frat detector was. an oscillating valve, quite the most
It may be that if wireless is to
Results are usually much better important part of the whole system, combined with the incoming oscilla wireless station of: Scotland Yard by trial and the size of the con tection and prevention of crime the certain direction to be found tions, producing a frequency equal
denser best suited to the circuit to the difference between the in-will have to be transferred to an- caning frequency and the oscillator other district free from this direct should also be droided upon after frequenoy. In other words n beat frequency was produced.
Suppose the incoming signal fre queney was 1,000 kilocycles and the local oscillator was 1,031 kilocycles The new frequency appearing in the ariodo circuits of the first detector would then be 34 kilocycles, or the difference between 1,000 and 1,034 kilucycles.
interference.
testa,
Usually the condenser should, be FlySquad dara,
one of small capacity, such as .0003 microfarad, or even less. And cause the Scotland Yard system of small condensers of this capacity This is the more feasible beit must be well insulated, Some communicating with Flying Squad might easily break down, for it In the majority of districts the cars has not always been successful. must bo remembered that one side-
is connected to the maine and the messages are easily picked up, but other side to earth, through the if a police car is patrolling a road coil. where there are overhead tramway The arrangement of the aerial wires there is interference with the wire in the act is of some import- reception of messages, from the c When therd, are high-fre
Quency stages not completely.
The "value of such a change is obvious; the long-wave signal could be amplified, whereas the short wave signal could not. As the long-Yard,
pro-wave amplifier gave its greatest Another curious fact is that shielded couplings may exist be
10.30 p.m.-Rugby mid day Press ... дена. 10.33 p.m.-Close downt
Engineering Features:
FOR
a
amplification at one fixed tuning Flying Squad car is never able to point in the long-wave, bant, it use an electric windscreen wipes: was obviously necessary to make The effect of this is to drown the the local oscillator beat with the in-sound of any message being sent out coming oscillations to produce, this from the Yard. predetermined fixed intermediate frequency. All that meant was on
adjustment of the oscillator. A how the selective properties of the the incoming wavelength ehinnged,
Advanced 1932 Models irrcapective of wavelength.
Superheterodyne 8-TUDE BURERURTERODYNE
RADIO
FREE SERVICE
TO PATRONS
CHASSIS (3-SCREEN-GRID &",
2-245 TUDES)
TONE CONTROL LOCAL-DISTANCE SWITCH EXTENSION SPEAKER JACK TEN K.O. SELECTIVITY "SENSITIVITY -BEDUCED
NOISE LEVEL ILLUMINATED
DRUM DIAL FELL TONE
MOVING COIL SPEAKER
No BEPEAT POINTS-
No OSCILLATION COMPACT SIZE
OHABSIS ONLY 127
FOR FURTHEE PARTICULARS, APPLY TO:
THE WING ON CO. LTD.
22687).
OF DISTRIBUTORS.
72726672
The Old Type.
tween the aerial wire and the air- cuits and so cause instability and poor magnification.
Push-pull and Bias,.
The practice is growing of ar push-pull amplifier ranging that tho, two valves of o shall have so was the wavelength of the oscil-super-het have been neglected. We separate acid-bins. The adjustment lator. The result was equnt ampli- have been building sote with ns of the grid bins is becoming of more fication of all incoming signals, have had to suffer from all the in- they have relatively high slopes.
many as four toned circuits and we importance with modern valves, ns equalities of amplification over a Unless the valves are carefully wide tuning range, forgetting that chosen, the best-results-will-certain- So much for the answer to the tivity needed with the variation of bias for the push-pull stage The the super het gives us all the selec-ly not bo obtained with a single question as to what is the super-het. only one tuning circuit. Now why did it declino in favour Sets have been developed to provide equal anode currents bias, adjustment should be made The main TEASON was them with two high-frequency amplify. through the two valves. provement in the properties of high ing valves and somtimes three, frequency valves and in the circuits involving three of four tuned slope type, the effect of slight With small valves of the steep. for them. We had the neutralised circuits, all of them continuously changes in bins is usually most circuit for the three electrode, high-variable from 200 to 600 metres and marked. The result is that poor frequency amplifying valve; more 1,000 to 2,000 metres. Few, if any, resulta will be obtained if the pre- recently the screen-grid valve, has como along to give us stable, and amplification over the whole tuning not taken.
of these sets can claim to give equal chution of setting the two values is appreciable high-frequency ampli-range explored by the ganged con fication on wavelengths between denders And the ganging of the
A Handy Meter. and 600 metres. To-day we can scveral tuned circuits is by no provide as much high-frequency means always true. We have ar signals as is needed to load the straight it where complexity is williammeter having a range of. One of the most valuable instru- amplication of medium-wavelength rived at a development. in the ments that you can have is a detector valve to the fullest possible just as great as in the old super say, 0-5. Connect the after in the Another factor that helped to kill in a good straight set to-day there note how the current changes dur- het. If dye valves have to by used anode circuit of the detector and the super-het was the high running can be no objection to the super het ing tuning. cost. Seven valves" was about the as regards the number of "valves To begin with, the ourront may. minimum in a super-het having, needed. And since the really big h 3 milliamperes. When a strong say, first detector and oscillator,sets of to-day are of necessity mains signal is brought in the current. two intermediate high frequency drives the objection to upkeep costs will decrease, falling, perhaps, to stages, second detector and two is also fuled out. stages of fow-frequency applica- Even if we have to contemplate indication of signal strength.
milliamperes. This is a rough tion: The finment current of such battery operation the valves of to With some sets you can tune a net was about 5 amperes and there day are very much more economical much more accurately if the meter wore no super high-tension batteries to run than in the days when the is used in, this way. In sets having to cope with the considerable anode current. Nor had mains power beenfilament and and current have the tuning is much simplised and super-het was widely used. Both band-pass circuita, in particular, developed.
extent, as
been enormously decreased batter quality of reproduction In It Coming Back?
It is significant that two of should result from accurate tuning. America's leading electribal organi Now we come to the question as sations have adopted the super het valuable. You can match up the In ganged sets the meter is very to why the wis per het is returning principle to this year's models soparate soircuite easily, the reads Firstly, because we now nood above British manufacturers can also eming of the meter decreasing show all else selectivity. It is curious ploy this principle since the recent ing a stronger signal, of couran, as (Continued on, ness Dolumn) clearing up of the patent situation:. Continued on Page 2)" ||
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