NOISES AND FADING OCCUR WHEN EARTH IS POOR

Wanganui Chronicle, Volume LXXXIII, Issue 19914, 9 August 1927, Page 10

NOISES AND FADING OCCUR WHEN EARTH IS POOR

ARE YOU SURE THAT YOUR EARTHING IS GOOD

A circuit or a set is often blamed for poor performance caused entirely by a poor aerial or a poor earth. The latter is often the source of trouble because the aerial being more obvious, perhaps, it is less subject to neglect. An operator, realising the value of height, and appreciating too that screening exercises a detrimental effect. takes care to sec that his wire is slung so that it may function to the best advantage, but an earth —well, it is just an earth. So it remains among those things that are almost foigotten. Successful listeners are those who realise that the earth is a part of the aerial system, and have the good sense to so arrange matters that the functioning of tlje set shall not be handicapped by inefficiency in any part of the antenna arrangements. The biggest bugbear to perfect reception is resistance in the wrong place, and one wrong place is the earth lead. No one would dream of permitting resistance in the aerial, and yet such is permitted in the earthing in too many instances. This resistance necessitates the employment of more reaction than is good to use and, even then, results must be poor because, when reaction alone is depended upon for volume, tone has to suffer. Pafths of High Resistance. But, apart from this, resistance in the aerial-earth circuit “hardens” the path over or through which oscillations travel. This means that, whilst powerful signals may come over pretty well, weaker signals cannot overcome the resistance and are lost—if we may use a very untechnical term to describe a species of damping that occurs. The many complaints received relative to the difficulty encountered in tuning distant stations point only too clearly to poor earthing. This may take the form of long, thin high-resist-ance leads, to corroded joints, or to the employment of an earthing agent totally unsuitable. It is rather a pity that so many textbook authors advise the indiscriminate use of a water-main earth. This may be OK in the majority of cases, but it is not always so. A water pipe may enter ground a few yards or even a few feet from the set to which it is

connected. On the other hand, it may travel for a considerable distance before doing so. During this distance there may be leaded joints, corrosion and matter which effectually resists the passage of current which, of necessity, must be weak. Not until aerial-earth oscillations have a free passage will it be possible to handle those puny signals put out I from distant aerials. I The moral is obvious. Do not use ! a water-main earthing system if it is found possible to utilise an independent means—that is, a short connection to a copper tube or a hank of copper wire buried in damp soil. If a water main has to be used, make the connection to it as near its entrance to ground as possible, and let the connection between joint and set consist of two lengths of 7.22 twisted together. This is by no means the first time we have given this advice. We may reiterate again. The point is of such vital importance that to over-tress it would be impossible. Effect of Poor Earth. We have said that one effect of using a poor earth is weak signal strength. There are others. Crackling noises may be occasioned, fading may be troublesome, whilst unstable tuning may completely foil the operator in his attempt to successfully comb the ether. A set which is nicely earthed will invariably function smoothly—other things being equal. This applies in particular to sets built to a circuit in which radio-frequency amplification is incorporated. Ultra oscillation, or selfoscillation may be directly caused by resistance in the aerial-earth system, I and no amount of artificial stabilising will supply a remedy. Look Around. Are you certain that your earthing is as good as you can arrange? Is your earth lead short and thick? Are all the joints in your system free from corrosion? Arc you sure that you can arrange no better alternative? Just ask yourself these questions. Look around. Make improvement if possible. Having done so, you will, at least, feel that you have done your best and are giving your set the best of chances to get on with its job.