AERIALS—INTENTIONAL & OTHERWISE

Radio Record, Volume I, Issue 37, 30 March 1928, Page 12

AERIALS—INTENTIONAL & OTHERWISE

The observant experimenter will often notice quite remarkable effects due to the proximity of an aerial not actually ‘connected to the receiver. At one t:me ‘it was usual to boast that one's set

would reccive certain stations without an aerial, and possibly without even an earth, Such a test carried out under home conditions probably involved disconnecting the aerial wire from the set and leaving it lying on the table near by, or at the most disconnecting the wire from the inside end of the leadin terminal. In both these cases more careful experiments will show that the aerial is still influencing reception, and it has even been noticed that an aerial is not quite inert if connected to an earth separate from that used by the set. Receivers are frequently tested nowadays to ensure that they will not receive even a powerful local station without an aerial. This serves as a test of the efficiency of screening boxes. To be quite fair to the set, however, it is important that there should be nu aerial, either of the frame or open type, | near by. ,

Other sources of unwanted reception are to be found in long H.T. and loudspeaker feads, particularly the former if a mains unit situated at some distance from the set is being used. The blocking condenser within the set between each H.T. tapping and earth should not be omitted even though there is a full set of condensers in the eliminator; and again, if long loudspeaker leads are to be used, it is desirable that an output transformer, the core and secondary of which are earthed, should be employed in the plate circuit of the last stage in the set. The use of a frame aerial will endow mlost receivers with a marked degree of selectivity, which is in no small degree due to the directional property of the frame; but here, again, care should be taken to ensure that there is not a lead-in from an open aerial close by, or persistent jamming by the local station may be experienced. It is a good plan to mount coils with their axes vertical wherever possible, as, if otherwise placed, they may be acting as miniature frame aerials within the set. Certain special arrangements of windings, such as the toroids and the binocular coils, tend to prevent trouble from this source.