On Short Waves

Radio Record, Volume II, Issue 27, 18 January 1929, Page 32

On Short Waves

The Use of Adapters

SHORT-WAVE telephone is being used by a great number of stations in many parts of the world, and any owner of a valve set with the aid of a short-wave adapter may listen to these stations. The chief difficulty appears to be that operators of broadcast receivers who are used to comparatively easy tuning and strong signals from nearby stations find extreme difficulty in getting a short-wave set to function. It should be clearly understood that in order to tune in these long-distance stations the detector valve must be ci able of oscillating. . It is often found that if a short-wave adapter is apply to the broadcast receiver, that the reaction condenser of the adapter can be turned all in without causing the detector to oscillate. There are two conditions which are likely to cause this. The valve used as a detector in the short-wave adapter may be unsuitable, or the plate pressure may be insufiicient. A great number of broadcast receivers will work very satisfactorily with from 16 to 223 volts on the detector, and as the detector valve is taken out and replaced by the adapter, the same plate pressure will be fed to the detector in the adapter circuit. In order to bring the detector in the adaper circuit into a controllable oscillating condition a B battery pressure of from 45 to 60 volts is frequently required. It will be clear then that it will be necessary very often to change ythe detector tap on the B battery in the broadcast receiver to a higher value if the detector tube in the short- | wave circuit fails to oscillate. The reception of telephony is largely a matter of perseverance. The detector must be in an oscillating condition to first find the carrier wage of the distant station. It is here that the skill in tuning in the telephony is required. It merely. consists of gradually reducing the oscillation and compensating on the tuning dial until the whistling carrier is smoothed out and the voice or music is cleared up. Provided the detector is capable of oscillating and being throttled by the convol condenser, and that the correct coils are in for the particular wave length, it is desired to receive no difficulty should be experienced after a little practice in finding the inter national telephone stations. .