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ele. - sr--- AN D RADIO REVIEW (17Th Year of Publication) No. 5i0. WEDNESDAY, JUNE 5TH, I929. VOL. XXIV. No. 23. in excess of what is really necessary, and it becomes Editor: HUGH S. POCOCK. desirable to reduce the efficiency of the H.F. ampli- Assistant Editor: F. H. HAYNES. fication in such a receiver in order that the detector stage Editorial Offices: x 16-1E17, FLEET STREET, LONDON, E.C.4 shall not be overloaded. This all means that we have Editorial Telephone: City 9472 (5 lines). reached a position where an outside aerial becomes un- Advertising and Publishing Offices: necessary and, apart from its inconvenience, it may be DORSET HOUSE, TUDOR STREET, LONDON, E.C.4. hues). Telegrams: "Ethaworld, Fleet, London." even quite undesirable to employ its because with a set Telephone: City 2847 (13 in COVENTRY : Hertford Street. giving high amplification the outside aerial brings Telegrams: " Cyclist, Coventry.' Telephone: 6210 Coventry. a great deal of interference which can be, to a certain Street. BIRMINGHAM : Guildhall Buildings, Navigation extent, reduced by the employment of a frame aerial, Telegrams: " Aotopreee, Birmingham.' Telephone: 2970 and 2J71 Midland. MANCHESTER : 260, Deansgate. largely on account of its directional properties. Telegrams: "11í5e, Manchester." Telephone: 8970 City (4 lines). From the point of view of convenience, there is much GLASGOW : MI, St. Vincent Street, C.2. in favour of the portable, and it is not sur- Telegrams: "HiCo. Glasgow." Telephone: Central 4827. to be said PUBLISHED WEEKLY. prising that statistics show a very pronounced increase Subscription Rates: Home, 17s. 4d. ; Canada, 17s. 4d. ; in the demand for portable types of receivers during the 19s. 6d. per annum. other countries abroad, few months. Entered as second Clam Matter at New York, N.Y. past covered by A s many of the circuits and apparatus described in these pages are patents, readers are advised, before making use of them, to satisfy themselves Aerials Superseded by H.F. Amplification. that they would not be infringing patents. Reverting to the question of the outside aerial, its history can be traced from the early days when coherers, CONTENTS OF THIS ISSUE. and later, crystals, were the only detectors available, PAGE EDITORIAL VIEWS .. .. .. 573 and when amplification was unknown. The advent of THE MODERN PORTABLE .. .. .. .. 574 but, even CURRENT TOPICS .. .. 678 the valve changed the position considerably REPRESENTATIVE PORTABLES REVIEWED .. 570 so, until H.F. amplification was introduced one could BUYERS' GUIDE TO PORTABLE SETS, 1929 .. 585 HINTS AND TIPS FOR PORTABLE USERS .. .. 600 riot dispense with an outside aerial except in the case of B2OADCAST BREVITIES .. 601 A "PARATUS REVIEWED .. 002 long -wave and very high -power transmitters, without PORTABLES NEED NO APOLOGIES. 'By B. H. DAVIES 604 an entirely uneconomical extension of low- frequency am- LETTERS TO THE EDITOR .. .. .. 606 READERS' PROBLEMS . .. .. .. 608 plification. For a year or so past when using sets em- ploying, say, one good H.F. stage, it has been the prac- tice of those seeking for selectivity to reduce the size ARE AERIALS OUT OF DATE ? of their outside aerials very considerably, and the more "VIANY of the earliest portables which appeared on efficient the H.F. stage the smaller the aerial which the market in this country were not the products was necessary for the degree of amplification required of the established radio manufacturing firms, and the better the selective properties of the receiver. and the explanation for this may probably be found The well -designed set of to -day employing two stages quite readily in the fact that the engineer dislikes corn - of screened -grid H.F. amplification can comfortably promise of any kind, and would rather sacrifice con- afford to dispense with an outside aerial altogether, and venience than put forward for production a design which so we see the increase in the popularity of the portable he considers to be technically inadequate. as a direct result of the great advances which have been This was the state of affairs a year or so ago. Unless made in H.F. amplification. It seems likely that as one was prepared to employ many more valves than time goes on the unsightly outside aerial will disappear were economic or strictly necessary for satisfactory re- almost entirely from the chimneys and the back gardens, ception it was not a practical proposition to dispense and those that remain will brand the user as the owner with the outside aerial. But to -day a new situation has either of a crystal set or a very inefficient valve receiver. arisen. If one uses an outside aerial the employment In fact, the demise of the outside aerial, which would of two stages of H.F. amplification is very desirable probably take place in any event as a direct result of as a means of attaining the selectivity necessary in these technical developments, will be hastened by reason of days of crowding of stations and high power local trans- that same characteristic of human nature which registers mitters. Now, having admitted that for best results we dislike at driving a car preceded by a starting should use two tuned H.F. stages, we find that with an handle in these enlightened days of electric self- outside aerial we have at our command amplification far starters ! A II . www.americanradiohistory.com 574 'Pfip@Ilsggi JUNE 5th, 1929. W®pIll i NO longer is the portable set the synonym of out- we shall have two outstanding types of receiving sets door reception. It has passed from the position is a safe prediction -the generous all-mains quality of the least satisfactory of radio receivers to one with moving -coil loud speaker and, as its junior, of omnipotence. Out -of -doors use with the picnic party more modest self -contained set which up to the or in the car, so generally visualised as the purpose of present has been known as the portable. the portable, is now but a minor application. In that progress is revealed by change of practice The fact which has made the portable the typical we find many interesting facts in comparing receivers receiver of to -day is that it can be built without need of this season with those of a year ago. We look first for undue compromise in design which might prejudice for any wide disparity in a summary of the features performance while giving the great advantage of a self - of the designs, and next for examples of new and out- contained set devoid of external connections. A concen- standing practice. As there is not a downward trend tration on the production of in the number of amplify- portables by practically all ing stages used in this year's manufacturers has been re- No longer is the portable a specialised class of receiver portables as expressed by garded in many quarters as involving compromises in design that may impair its per- a percentage representing formance. a passing phase ; yet we are Neither is the portable any longer regarded as those sets fitted with five an out -of-doors forced to admit that it now set but rather as the ideal popular receiver valves it might be thought for home use. The high -power London station at holds the field as the lead- Brookmans that the single efficient Park which is shortly to replace the 2L0 equipment ing type of radio receiver. will H.F. stage as well as the further encourage the use of the self-contained set with Valve improvement is the pentode have not yet found foundation on which the enclosed frame aerial. Present -day practice is carefully analysed their way into portable re- portable builds. With the in this article ceiver and the facts disclosed should prove helpful to the amateur, design. Actually best valves of a year or so several manufacturers in ago, such the set builder and the designer. Portable set designs as the .o6 and are arrived at adopting the pentode out- 1 D.E.5 classes, only after considerable experimental work portable re- combined with careful testing, and put have replaced their ceiver the result of much designs suffered from experience is here revealed. five -valve receivers with many defects. It is not un- four -valve models. Be- duly difficult with the valves cause there are more sets of to -day to build a stable H.F. amplifier giving such a this year than last, the number of five -valve sets has high degree of magnification that the use of a small increased to 75 per cent. of the total for all types, yet frame is preferred to the elevated outdoor aerial. Ample this year there are r8 per cent. sets in which the pentode low -frequency amplification can now be obtained with- is fitted either as standard practice or will be supplied out the sacrifice of quality, while the apparatus em- if required, as against last year without a single in- ployed is less heavy and more compact than formerly. stance. Particular two- and three -valve sets of last Most important of all is that concurrent with the year have disappeared, whilst new ones incorporating advance of the portable comes the commencement of the pentode have maintained a figure of ro per cent. the regional scheme. London listeners will shortly be for receivers of this class. within the shadow, almost, of a station of 5GB dimen- It was surmised last year that there would be a sions, and it is safe to predict that attention will be tendency to simplify tuning in the direction of a re- turned to the self- contained frame aerial receiver. That duction in the number of sets fitted with two -dial con- A 12 www.americanradiohistory.com JUNE 5th, 1929 Wp®Ilsoo 573 Ilca TWO WAVE RANGES ONE DIAL 96% TUNING 5570 PORTS EXTERNAL AERIAL TERMINAL 55% I ° VOLUME CONTROL APART FROM REACT" 8% GRAMOPHONE PICK-UP 26% XTERNAL L565% 15r L.F COUPLING 211.° L.F.

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