CENTS COPY / The Hammarlund Short Wave Manual 1935 EDITION this manual will he found the constructional details on Generally speaking the larger the wavelength, the later in INwhat is, probably, the most carefully selected and compre- the day will best reception occur.The 16 meter broadcast hensive group of inexpensive short-wave receiver designs ever stations, for instance, are best during the morning hours. Those published in a single volume. operating on 19 meters come in well during the late morning The selections were made by the editors of five of the lead- and early afternoon hours.The 25 and 31 -meter stations ing radio publications of the United States, from among the usually are heard with maximum volume during thelate most popular and efficient designs described in their publica- afternoon and early evening hours and those on 50 meters tions during the past year or so.Then models of the re- are best received after darkness has fallen. ceivers were constructed and put through their paces in the The foregoing holdstritewithfewexceptions in North laboratory and "on the air" with the result that the twelve America.One of these exceptions is reception from Austra- designs presented here represent the cream of the hundreds lasian stations.These operate around 31 meters, yet are heard offered to the home constructor during past months. best by Americans in the early morning before breakfast (at Inasmuch as the most popular designs are the more simple which time itis evening in Australia and New Zealand). ones that combine low cost with efficiency, the receivers de- There are explanations for the conditions mentioned, some scribed here naturally fall in that class.The requirements of of them being rather involved.However, the important thing, the constructor who is looking for more advanced design are front the standpoint of the short-wave listener, is that these not overlooked however.Then, too, while the demandis conditions do exist.They can that the old practiceof sitting greatest for short-wave broadcast receivers, the special require- up all night for good DX reception is a thing of the past,and ments ofreceiversfor operation on the that practically any waking hour is a good amateur bands have not by any means been one for foreign DXreception, on one wave- neglected asis indicated by the fact that lengthoranother in the short-wave range. band -spread designs, and even a 5 -meter re- ceiver have been included in this group. Tuningashort-wave receiverisafar Having arrived at the final selection of more criticalbusinessthanisthe same receivers, the nextstep was toturn the operationonthe broadcast band.This is models overtothe experimentallabora- not due to any electricalpeculiarities in- tory for careful study to determine whether herent in the short waves, and is best ex- any of them could in any way be improved. plained by an arithmetical example. The fact that several of them came out of Assume that a receiver is capable of sep- this laboratory with improvements should arating stations which are broadcasting at not be taken as a reflection on the original frequencies10kilocyclesapart. Inthe designers or the publications in which the broadcast band of 1500 to 550 kc. there original descriptions appeared. The changes would be room for 96 such station channels. made mainly took the form of substitution If the tuning dial were properly marked off of more modern tubes or more efficient in 96 divisions, therefore, a station would be coils, with some changes in associated parts heard at every division on this dial to adapt them to these new units.In a few other instances changes which brought about a considerable improvement in Now, going down to the short -waves, the tuning rangeof a efficiency at a slight increase in parts costwere considered justi- single coil may be from 20 meters to 50 meters which means, fied and were therefore made. in terms of frequencies, from 15,000 kc. to 6,000kc.Instead ofproviding for96 channels there would be 900 such 10 - In some respects reception of short-wave signals differscon- kilocycle channels and with the same dial marking as men- siderably from reception of signalson the broadcast band tioned above, there would be 10 channels to every-division of above 200 meters.Perhaps the most prominent difference is the dial instead of only one.It therefore follows that in tun- found in the astonishing distances that can be covered with ing the short-wave stations the adjustment of the dial has to eventhe most simpleone or two -tube receivers.Itis no par- be exact to a small fraction of a division. A high radio tun- ticular feat, for instance, to hear the European stations and ing dial is one way of accomplishing this. others from remote parts of the globe quite regularly with such receivers. Undoubtedly the most practical method is found in the use of some sort of band -spreading system.The most common of Such distance reception is not limitedto the hours of dark- these is the one in which a small variable condenser is con- ness, as is DX reception on the broadcast band.In factsome nected directly across the regular tuning condenser,the small of the most phenomenal receptionisobtainedin the day- condenser being employed for the exact tuning.Take as a time. (Continued on nese page) THE HAMMARLUND MANUFACTURING CO., Inc. 424438 West 33rd Street, New York, N. Y. Edition fully Copyrighted 1934, Iternmarinnd Mfg.Co.,Inc. Printed in U.S.A. 2 T he HAMMARLUND specificexample ashort-wave receiver Some points of ineffieiency are gener- withItroil plugged in, which covers the ally recognized.In the matter of insu- rangeof 20 to 50 meters mentioned above, lation,forin -tame, the average short- and employing a timing condenserof 140 wave enthusiast haslearned that nothing nimid. maximum capacity.UOtating this short of the lastis good enough.'this condenserthroughitsentirecapacity explains the almost universal preference range tulles thereceiver through afre- for Isolantiic insulated tutting condensers quency rangeof 15,000to 6000ke.,a and coilsockets.There are, however, span of9000 ke. or 900 10-kc. channel,. other factors which are less often con- Now,suppose a shuntvariablecon- sidered.Perhaps the most important ul denser of much smaller capacity isplaced these is the plug-in coil. ger., this 110minfd. condenser. Swing- A recent study of the low and medium - ing chi= small condenserthrough its en- mired plug-in coils available on the open tire range will result in arelatively small market showed them to have an average rapacity variation and therefore arelit. "Q" of approximately 100(at15 mega- tiN ely small frequeney range.With the cycles) whereas the "Q" of a perfect coil selection of the proper small capacity, for should approximate 200.Inasmuch as Instance, thefrequency range with the "0" represents the efficiencyofacoil smaller condenser may be only1/1.0th inatunedcircuit,theimplicationof as great aswith the larger condenser and SHORT WAVE FANS IN JUNGLES 01' these figures is obvious.In actual prae- in such a ease therewould be only 90 MALACCA tire.a"Q'.ol200is not obtainable in channels within the range of this con- A group of Jungle Dwarfs (theSakai) practical plug-in coils because of certain denser,tuning would become asnon- tuning in on a short wave regenerative inherent losses introduced by the metal critical as that in the average broadcast - receiver brought to them by Frank. Buck. prongs of the coil form, metal nearthe baud receiver. The variably condensers, sockei, coils, roilwheninpositioninthereceiver, etc. are all HAMMAID,lN.D. etc. When this systemis employed no ad- Hatesnarlmul has made high-grade plug- ditional coils are required and the only and a host that in coils for years, but these have been extra cost is that of thesmall condenser. modern superheterodyne beyondthepurseoftheaverageset '1'lle large condenser is employed to tune swear bythe regenerative receiver. acarefulin- saidfor both builder. however, after the receiver into the particular hand de- Thereismuch to be vestigation, the conelus' wasreached sired, say the 25 meter broadcast band, types of receivers.Where asinglere- boil,the that plug-in coils of excellent character- for instance, then the small condenseris eeiverisrequiredtocover istics could be prodneed to sell at a low employed to tune in the stations within short -waveandbroadcastbands,the price, especially as much of the research These stations will then he. superheterodynereceiverundoubtedly that hand. superior se- and development 'work involved in such spreadoutoverperhaps 15or21) de- has the edge because of its an effort had already beenaccomplished grees on the hand-spreaddial whereas lectivity onthebroadcasthand. For can in producing the coils employed in the they would fall within I or 2 degrees if purely short-wave work it safely be general types of Hattimarlund "Pro" receivers.The de- toned onthedialof thelargercon- said that either of these sign workWastherefore started and the denser alone. receivers,ifwelldesignedandcons new coils are now WIthe market at the strutted, is capable ofexcellent service. same price as ordinary coils.The forms Variable condensers, such as the Ham- Among those who "build theirown" employed in these new coils marlund Type MC -12013,areavailable the regenerative type of receiver isby far of XP -53, an exclusive Hamm:wham' pro- whichare especially intendedforpar- the most popular.Itis less costly, easier duct developed for this purpose.In this allel band -spread use.These are made to build, more easilyunderstood by the new