Wireless Broadcast

Star (Christchurch), Issue 17350, 15 May 1924, Page 13

Wireless Broadcast

CONTRIBUTED BY

“AERIAL."

THE COCK ADA Y FOUR-CIRCUIT TUNER. Probably one of the best receiving stations m New Zealand is tn© one owned by Mr L. fepackman (IAC), A nek land. Many peopie scattered e,li over the Dominion have heard of his wonderful results, arul large numbers have written to the gentleman, asking lor information on his set. Mr Spackman’s description is worth reading.

The extraordinary sensitivity of the receiver is duo to several things ; first l>y reducing ail losses to a minimum; by tile use ot the highest-grade material and instruments and proper design ; by the use of the single turn primary whch is coupled to a Go turn secondary, giving a step-up ratio of 1 to 66, which makes lull use of the amplifying properties of the valvo which is a potential operated device. The absolute stability of the circuit enables the vaivo to be set in the ‘‘just oscillating'’ condition, irrespective of changes in any of the tuning dials, or outside influences such as static, etc. The circuit is the wellknown ultra-audion, a sensitive and steady oscillator, but one which is very hard to control as a rule. In this tuner howecer the difficulty is overcome by means of « stabiliser circuit, which allows very tine control indeed. The set is loose-coupled—much looser than is attempted in almost any other typo of circuit. The only coupling between the aerial and secondary circuits is by means of a single turn, at a distance of about two inches from the secondary, this giving the set its great selectivity.

To shop’ its sharp tuning qualities, the set at IAC only needs to have the tuning condenser moved one degree to completely eliminate the broadcast station IYA which is located only a mile and a half away from IAO. Unless the dials are turned very slowly and carefully, one is apt to tune past even local stations without even hearing them. When the receiver is properly tuned local stations paralyse the valve, and for best results from nearby stations the set .may be switched on to a small indoor aerial, or else the outside aerial may be left on. but must be detuned considerably. The aerial circuit is roughly tuned by' means of a seveu stud switch which varies the amount of aerial loading coil in circuit.

Signals from Dg stations can usually be received over a range of three or four studs without much variation in strength. Tuning the aerial has no effect on the other elements; the

switch aim is merely rotated until the signals are at a maximum. Moreover the aerial can swing to its heart’s content without causing the receiver signal to be in any way affected. Consequently swinging and fading signals from this cause are nil. The aerial can be disconnected altogether, ■with the signal still remaining tuned in but somewhat weaaer. The regeneration can be set and will stay put over the entire tuning ijange. The control of regeneration .is positive and very simple.

IAC uses a U.V.200 valve as a detector. It has been in use several years and is ‘as good as ever. It has been lit by the “ B ” battery once for a few seconds—Li—and the filament for a little while leaned agaiust the grid, but e, little shake righted* it again, and the valve is still first favourite in Auckland. The U.V. 200 is a rather critical tube, but once mastered they are about the most sensitive. The whole is. contrary to most, sets, dead silent when in an oscillating condition, and a little doubt as to whether it is oscillating or not can be excused, until the grid terminal if touched, when the resulting “Plop” nearly bursts the ’phone diaphragms. Tho set is as quiet as a crystal detector and the faintest signals can easily be copied. The user of a four-circuit set can never be an “Oscillating Oswald,” and another great advantage is the fact that there is no body-capacity effect. Even shielding is totally unnecessary, if the wiring is done properly. Once a station is tuned in, tuning troubles are forgotten, and loud bursts of static do not disturb the setting at all, as is tl?e case with most tuners, excepting the poptSlar “Low Loss tuner.” For those who wish to make a tuner of this description full details will be lound in tlie March, 1924, issue of •‘Popular Radio,” and in “Radio” (U.6.A.) for October. 1923. In building follow all instructions in making tile tuning elements and the wire exactly. In the proper diagram the direction of winding for each coil is shown, including the single-turn primary. Various parts should arranged as the instructional articles show, us this has all been thought out for maximum efficiency. The secondary, stabiliser and aerial coils should bo wound on their hakelite formers, cardboard making a poor job, and introducing some rather high losses. The stabiliser variable condenser should have a capacity of ,(X)OS mfds, and the secondary condenser can be smaller, .0003 mfd being sufficient to give a tuning range of 135 to 500 metres. At IAC the circuit works well with any of the VV tubes, fair with the WDII, and not at all with English tubes, as their impedance does not suit the circuit. There is a knack in operating tho receiver, and the builder must bo prepared to spend a week or two learning to tune it. On turning both dials a click will be heard at a

certain point. This is due _to the cessation of- oscillation, and is the most sensitive point, and for Lett results the two dials should be adjusted so % that signals are received at this point. When tuning in distant music, turn both dials together, keeping the carrier tuned m, until this point is reached, when the receiver will cease oscillating and the carrier wave lost entirely. Now adjust the filament for the best resulls This sound* complicated, but in practice is quite simple, and once the knack has been mastered, the volume of sound obtainable from a weak carrier wave is really surprising. To date on this receiver Mr Bpackman has received 270 U.S. amateurs, cght U S. broadcast stations, about 50 Australians and all New Zealand, also the receiver picked up the signals of 2CDM when 4500 miles away. Altogether a very satisfactory and at the same time exceptionally neat looking receiver. •JOTTINGS. Mr B. Withers, of local 3AM, had an unpleasant experience a few evenings ago. While throwing his change-over switch to the “send” position he accicame in contact with a live wire carrying 750 volts. The severe shock hurled the unlucky operator across the room and dazed him for (several minutes. I noticed that he did not come on the air again that evening. and T learned subsequently that he suffered a severe headache, and spent a very restless night. However, he is. on the job again. I'm glad to notice. Good thing it was 750 and not the usual 1500 volts OM. Don't do it again pleas©! The April issue of the “ New Zealand Wireless and Broaeasting News” is to hand, and there is some excellent reading between its covers. An article by Mr F. Bell, of IAA gives some very interesting side-lights on amateur wireless. amd details of the recent “ Chi-

cago Test,” which interested evervbody. arc published. Altogether tho current issue of New Zealand’s only radio periodical is more than up to the mark, so do your duty, and support local industry.

He’s don© it again ! This time with 1.0 amperes in his aerial, his voice and buzzer signals were heard very distlnctly by Mr Jack Davis (of 2CDM fame) on Saturday evening. Mr Davis’s ’phone came in well until it was jammed out by the announcer at 3AQ. Yes, it was 3AF who spoke to Sydney on a single five watter.

Yanks were coming in very strongly during the latter part of last week. Using detector and one step in a low loss set. a local man clearly heard California 6CGW calling WNP, the North Pole expedition 6hip. That was with the aerial totally disconnected from the receiver. With the aerial on. the Yank was easily readable on AC hum, with the receiver not oscillating.

3AM continues to get Jjis signals across the Tasman Sea. Last Saturday evening at 11. lo p.m. (when little ooys like 3AM should be in bed) I heard him having a chat with Aussie ABD, who reported his signals strong in Mel bo-.’rue. Here's another fivewatt wonder.

A Tot of people wonder what “ Hi ” means. It is a radio laqgh, or expression of .merriment, and also sometimes of sarcasm, depending on How and when the word is used. It is not as a rule, used as a spoken worci. but is an American abbreviation used by telegraphists, and is also used in writing. W T e understand it and it saves time and space. Hi !

A successful meeting was held by the R.S.C. last Thursday evening, in the W.C.T.U. rooms, Manchester Street. After the minutes were disposed of, and all business cleared up, the chairman (Mr L. Street) asked Mr Withers for a little talk on his station. The lecturer did not confine liis talk to a description of his own set, but instead took nis audience step by step, explaining the valve transmitter in general. At the conclusion of his very’ interesting lecture, Mr Withers (3AM) was accorded a hearty voce of thanks, on the motion of Mr H. P. V\ Brown. A meeting will be held to-night (Thursday) fit the usual place. Every radioist is heartily welcome. It is now reported that all German telegraphists in the “ Fatherland” are using the “remorse” code.

Just as I was handing these notes to the printer, comes the news that New Zealand 4AA has been heard in U.S.A. by ICMP, Massacbussets, at 9AVG. in Kansas, and in Alaska. The first is known by Mr Bell (4 AA) to be an error, but there is the possibility, nay probability, that the others are correct, especially as the New Zealand abbreviation intermediate sign (Z) was used. Congratulations to 4AA, anyway. COR RESPONDENCE. J. 8., Fendalton. asks :—Would his circuit (enclosed) be all right for adding one. step of R.F. amplification to Mr Whiteley’s circuit, which was published last week. Yes. you circuit is quite O.K. and would probably be even better if the coil in the plate circuit of the first valve were shunted with a variable condenser. If your detector tube is a “ soft ’’one the lead from the tickler coil should b© capable of being placed on any portion of the “ B ” battery instead of using all of it. In the case of a hard valve, or a similar one to the amplifier, your circuit is correct. I believe the aerial wa,s either one or two wires about thirty-five feet high. No date on size of wire, but gauge TT. a.c.c. should be quite suitable.