Learning by Experience

Radio Record, Volume IV, Issue 42, 1 May 1931, Page 15

Learning by Experience

Aerial Resistance *WO experiences I have had lately; one a rather expensive item, might be of interest. I was adding a stage of audio to my short-wave set, the transformer had its four terminals in a row on top, B + G bias, G. and P. I was experimenting with the grid bias and disconnected the wire from the. bias terminal, and a slight movement caused

— this wire to make contact with the, RB + 90 volts. There was a flash, and three good valves went west. Moral, always disconnect H.T. when tinkering with your set. My second experience goes to show how necessary it is for a good insulated aerial. I built up a kit set for a friend, and it worked ‘well at my house. When I connected it to my friend’s aerial reception was poor. I took it home:again, tried it again. All O.K. Back -again to my friend’s house, no better result than before. I suggested his aerial may be leaking.to ground, so I tested my aerial with a megger. The reading was infinity. When I tested that of my friend all I could get was 6 megohms, so that he was losing about 70 per: cent. of his signal strength. We unhooked the aerial at the lead-in and got the infinity test. The whole trouble was’at the lead-in, which was a piece of wood nailed to keep the aerial from touching the spouting. After this all was satisfactory. In discussing the subject with a friend I suggested making a test of his aerial, when we found a resistance of only 4 megohms. When the aerial was disconnected it read infinity. His lead-in through a brick wall was the source of much energy being lost. No one was more surprised than he, In my opinion, one of the main causes of bad reception is an inefficient aerial. A megger test is the most conclusive one that can be applied to any installation, -T, P. Sewell (Christchurch.) ~