THE WIRELESS WORLD AND RADIO REVIEW THE OFFICIAL ORGAN OF THE RADIO SOCIETY OF GT. BRITAIN Na 14. JULY 1923. WEEKLY No. 20 3 [VoL . XI I. 7th, EDITORIAL AND PUBLISHING OFFICES : band of from 35o and 42o metres, and the The Wireless Press, Ltd., 12 and 13, Henrietta St., latter on 60o metres, must certainly overlap Strand, London, W.0.2. when reception is arranged with a single Telephone: Gerrard 2807 -8. circuit tuner, and interference must arise in EDITOR : HUGH S. P0000x. view of the fact that ship stations usually RESEARCH EDITOR : PHrr a R. OouasaY, employ a power of 1 kW. B.Sc., F.Inst.P., .4.M.I.E.E. Attention was drawn to this interference by ASSISTANT EDITOR : F. H. HAYNES. Prof. Marchant in his recent paper before the Questions and Answers Department : Under Radio Society of Great Britain, in particular the supervision of W. JAanss. with regard to the difficulties experienced in lHE EDITOR will be glad to consider for pub - the Liverpool district from approaching ships ication articles dealing with subjects within the scope of the Journal. Illustrations should pre- and a busy land station. ferably be confined to photographs and rough drawings. It is hard to suggest what should be done The greatest care will be taken to return all illustra- to remedy this trouble. It is quite obvious publication if tions and manuscripts not required for that it would be a very difficult matter to alter these are accompanied by stamps to pay return postage. All manuscripts and illustrations are sent the wavelength band for ship working as the at the Author's risk and the Editor cannot accept present equipments would not allow of any responsibility for their safe custody or return. wide change from that at present allocated, copies Subscription Rates : 20e. per annum, post free. Single whilst on the other hand there are so many 4d. each or post free 5d. Registered at the G.P.O. for trans- mission by Magazine Post to Canada and Newfoundland. broadcast receivers now in use designed for ADVERTISEMENT MANAGERS : reception only on the existing broadcast band BRRTRAM DAY AND CO., LTD., of wavelengths. g and to Charing Cross, S.W.I. Telephone: Gerrard 8088 -4. It would seem that the only solution would be to stipulate sharper tuning for the 600 Spark Interference on Broadcast Wave- metre spark transmitters. Looser coupling lengths. of these transmitters, and more care in tuning, It is necessary to seriously consider the might have the desired effect of reducing difficulties experienced by listeners -in in interference to a satisfactory extent. Ship coastal regions to short wave and broadcast stations are now usually equipped with either telephony arising from interference by ship synchronous rotary or quenched gaps, which stations transmitting on flatly tuned spark are specially designed for the purpose of re- systems. ducing damping in the transmitting aerial Letters are continuously arriving drawing circuit, but whether or not such apparatus attention to the impossibility of receiving is functioning efficiently and achieving the broadcasting with apparatus of the type usually desired object, is a matter of conjecture. sold for the purpose, and attention has fre- If broadcast reception in coastal towns is quently been drawn to the matter in the daily to go ahead, something must be done, and press. Complaints are also put forward by possibly a way out of the difficulty may be retailers of broadcast apparatus owing to their found by the introduction of regulations inability to guarantee that their apparatus defining the degree of damping to be used by will receive the broadcast transmissions in ship transmitting stations and careful observa- coastal towns without interference. Well modu- tion by the authorities as to transmitters lated telephony and highly damped spark emitting waves extending on either side of transmission, the former on a wavelength the specified wavelength band. B www.americanradiohistory.com 436 THE WIRELESS WORLD ANT) RADIO REV I EW .Tm.r 7, 1923 Development in Interference Elimination The recent Invention by Mons. Y. Marrec. W " \Vírcicss \Vorld" Photo. The apparatus comprises high and low frequency amplifiers followed by a low frequency oscillator, which is employed to heterodyne the detected and amplified signals. The pitch of the resultant note is regulated to suit a number of low frequency narrowly tuned selector circuits. Wireless Woild " Photo An hiker is operated by either the morse signals or the spacing between them. Successful demonstrations of the reception of American stations have been given in unfavourable surroundings in London on a frame LA aerial of seven foot sides without the slightest interference by 'jamming or atmospherics: www.americanradiohistory.com JULY 7, 1923 THE WIRELESS WORLD AND RADIO, REVIEW 437 Graduating a Barometer in Millibars. BY H. E. ADSIEAD, B.A. IT has for some years now been the standard practice to give the atmospheric pressure in millibars instead of inches. As old barometric instruments do not contain this graduation, I hope the following article will induce some to add it to their aneroids, etc. One advantage in so doing is that the eye becomes accustomed to the look of the J scale, and then the mind ceases to oppose a prejudice against what is a scientific improve- ment. What are millibars ? Those whose school days have gone a long way back may satisfy themselves by saying it is a " pounds -per- square -inch graduation in the metric system." - Pressure is always given as the quotient of a force by an area ; unit pressure is unit force on unit area. The metric force unit is a dyne, the area unit a square centimetre. This unit is very small, and a million such units are taken as the barometric unit and called a " bar," and this is about the average air pressure. To save decimals, we work in An Aneroid barometer with the new scale fitted, thousandths and say we have 970, 1,000, by means of which it is possible to take readings direct in millibar .t. 1,050 millibars, as the case may be, rather than 097o, 1.000, P050 bars. We are already eleven parts. It will not be necessary to employ accustomed to millimetres, milliamps, and so such an extended scale as this, about six of this should not be difficult of comprehension. these will cover most requirements. Draw The scale may be either white lines on black a larger arc of such a radius that it will fit film wrapping paper as in the photograph, nicely on to the aneroid face and produce or, for those who have no Chinese white paint, these six divisions outwards from the centre black lines on white. The former is the less on to it. Each is then sub -divided into ten obtrusive. The scale may be pasted on the parts and the larger units numbered from outside of the glass if the pointer is not too 970 to 1,030. This scale is inked in and cut far away. By the way, speaking of Chinese out and pasted on so that the division 999 is white, may I digress a moment. In a drawing opposite 29.5o as in the photograph. Those intended for 'photographic reproduction, no who are not accurate draughtsmen may pre- attempt should be made to erase erroneous fer to work on a circle of much larger radius lines, they should be covered up with dabs and produce their lines inwards on to the 4 of thick Chinese white, and the alteration will correct. arc. In either case a fine needle may be invisible. be stuck through the centre and the set square Returning to the main subject, we have swung round it in drawing the lines. If in the these two facts to go upon. A length of 3/ reader's aneroid the 29.5 does not occur at inches is equal to 110 millibars, and a pressure the top, one end of the scale, of course, will of 999.o millibars is equivalent to 29.50 inches need to be extended so as to centre it. of mercury. Take therefore a sheet of paper I wonder if readers have noticed how very < and draw an arc having the same radius as sensitive an aneroid is to changes of pressure. that of the aneroid scale. Along this mark If the hand is very carefully set and the instru- off a length corresponding to 31 of its inches, ment taken upstairs to the next floor, a slight and divide this by trial and error into exactly fall will be visible. www.americanradiohistory.com 0438 THE WIRELESS WORLD AND RADIO REVIEW JuLY 7, 1923 Improving Quality in Loud Speakers. The Filter Feed Circuit and Construction of an Instrument for reducing distortion. OUD speakers, in common with other magnetising force. It will be seen that the electro- magnetic reproducing devices, variation of magnetic field with the change of Jmay be divided, according to the magnetising force is not uniform, so that the method of winding, into two classes, known speech pulsations are not reproduced with respectively as high resistance and low resis- absolute faithfulness. The distortion is, of tance wound. The former are connected direct course, a minimum when the transformer is in the plate circuit of the last valve of the operated on the straight part of the curve. ti amplifier, and the windings consist of very many turns of wire, which is necessarily very fine owing to the small space available, the total resistance being generally 2,000, 4,000 or even 8,000 ohms. In the case of the low resistance type, the primary of a step -down low fequency (iron core) transformer is con- nected in the plate circuit and the loud speaker is connected across the secondary or low resist- ance winding of this transformer.