Radio Broadcast (May 1928-Apr 1929)

A S By HUGH S. KNOWLES CABLE. s> PLUG FOR SHORTWAVE RECEPTION The layout of parts for the short-wave adapter is simplicity itself, as this photograph shows. By the use of the correct coils in the plug'in set, it makes available to the ordiri' ary broadcast receiver the short wave-bands from about 8| to 200 meters IN THE article on the a.c. R. B. "Lab" receiver in the June Radio Broadcast mention was made of the fact that special provision had been made for a very valuable adjunct, namely a short-wave receiver which would extend the wavelength range of the set down to 16 meters. The use of short waves has become increasingly important during the past few years. At first they were considered the playground of the amateur— a portion of the spectrum with which he could amuse himself without interfering with "serious" business. Since that time they have showed such promise that they are in many instances replacing long-wave communication channels. An idea of what is being done in this respect may be gained by glancing at the list of shortwave stations published in the May Radio Broadcast, pages 44-46. This is the most complete and up-to-date list that has come to our attention. The receiver is simplicity itself. Like nearly all of the present-day short-wave receivers it uses a straight regenerative detector with no radiofrequency amplification. This is quite satisfactory because of the better field strength of the short-wave stations at moderate and long distances. The factors involving the attenuation or absorption of these waves are quite complex and so far only a few generalizations have been made, although a great deal of data has been collected. It is interesting to note, however, that t'l HE short-wave adapter described here can he 1 ■* used on any broadcast receiver, a.c or d.coperated. This unit is especially designed to be used with the a.c.-operated " Lab." receiver described in our June issue by Mr. Knowles. With it you can listen in the vast range of frequencies below 200 meters. It opens the "door" of your receiver and enables you to listen-in on the thousands of stations occupying a region which no broadcast-range set can cover. It is easily possible to hear England, Holland, and — at the proper time, before daylight in the United States-, — Java and Australia. This is not necessarily code reception, but voice and music. This unit can be used on the " Lab" receiver, operated from a.c, but a six-volt battery must be used for the filament: if used with a d.c. set, the regular battery is pressed into additional service. Mr. Knowles is now working on a long-wave attachment for the '' Lab" receiver that will broaden its usefulness in another direction. — The Editor. certain bands are valuable for daylight transmission when frequencies employed for broadcast transmission are unsatisfactory. this unit can be used with any set ALTHOUGH the short-wave adapter described in this article was especially designed to be used in conjunction with the fourtube a.c. "Lab" receiver described in Radio Broadcast for June, 1928, this unit can be used with any receiver which now is used only for broadcast reception on the usual wave-bands. This article describes what slight circuit changes are necessary when the present short-wave adapter is plugged into the detector tube socket of the a.c. "Lab" receiver; the instructions apply also to the use of the adapter in any other a.c. operated set. Those who have read of the experimental broadcast transmissions now being made from various stations in this country, in England, Holland, Australia and elsewhere will find the adapter described easy to build and successful in operation. [Other articles published in Radio Broadcast on short-wave receivers contain interesting and useful information about what is to be heard on these high-frequency channels. The reader is especially referred to Lieutenant 153