Changing Over to the Short Waves

Radio Record, Volume VIII, Issue 31, 8 February 1935, Page 45

Changing Over to the Short Waves

Types of Set to Use.

THE short waves are steadily increasing in popularity, if one is to judge by the number of receivers, converters, and adaptors that are now available. for the shortwave listener (writes A. W. Beatt in "World Radio.") The majority of nearly 100 powerful shortwave stations throughout the world are receivable on simple apparatus, providing one searches for them at the right time. Conditions on the short waves are not like those on the medium and long waves, Since the short waves are not limited as to distance. If the wavelength to suit the time of day and year is used, very little power suffices for transmission to.practically any point of the globe. Types of Apparatus. One cannot, however, be as certain of what is to be received on the short waves at any given moment, as of what is to be heard on the medium or long waves, It is, therefore, un advantage to be able to switch over from. one band to the other with as little trouble as possible to ascertain whether conditions are favourable or uot. The "allwave" receiver reduces the amount of trouble involved in the change-over to the flick of a switch, and if a run over the dials reveals nothing of particular interest, the change back to the broadcast band is just as easily accomplished. The all-wave receiver would thus appear to be the most suitable for the non-technical listener, whose interest in the short waves extends only to the programmes, news items, etc., receivable. The short-wave "fan," however, often constructs or purchases a receiver designed for use on the short waves only, or, alternatively, uses a a short-wave converter in conjunction with a broadeast receiver. Converters and adaptors of various types are available for attachment to existing receiv-_ ers, and bring most of the advantages of the all-wave receiver. There is a little

more trouble involved in changing over from one waveband to another, although simple switching arrangements can be provided to avoid the necessity of changing over connecting wires. A simple method of converting the broadcast receiver to the short waves is by means of a_ detector-adaptor, which may be plugged into the detector socket and requires only the additional connexion of an aerial and earth. Another arrangement is the single-valve superheterodyne converter, which makes use of both the H.F. and L.F. stages of the broadcast receiver. The growth of short-wave listening has brought with it the problem of reradiation from oscillating receivers, and both the detector adaptor and the single-valve superheterodyne converter can be offenders in this respect. Methods of suppressing possible re-ra-diation consist, briefly, in placing a stage of tuned or untuned H.F. amplification before the detector stage. This addition also has the advantage of stabilising the working of the detector. and eliminating "dead spots" caused by aerial resonances. For those who require something more sensitive than the detector-adap-‘tor, there is the two-valve superheterodyne converter, which changes the frequency of the incoming short-wave signal, so that it may be amplified by the H.F. stages of the broadcast receiver. as in the case of the one-valve converter.