HINTS FOR AMATEURS

Sun (Auckland), Volume II, Issue 403, 11 July 1928, Page 14

HINTS FOR AMATEURS

HELPING RECEPTION The first thing to bear in mind in connection with long-distance reception is the simple fact that the signals picked up by the aerial are so extremely weak that the set must be unusually sensitive to make the sounds audible in the phones at all. It follows that unless sufficient energy is passed on to the rectifier, nothing will be heard, hence in the large majority of cases high frequency amplification is essential to magnify the impulses received in the aerial until they are sufficiently strong. By the way, the crystal is quite unsuitable in a multivalve set, because it is unable to handle the large amount of energy satisfactorily; after a time it seems to become choked up, and signals become muffled and distorted. This kind of thing often occurs in reflex sets, which makes use of crystal detectors, and a good deal of distortion is thus caused. Damping It is important to keep down the damping in the grid circuits. This damping is the result of several causes —coils wound with too fine a wire, a high resistance aerial and earth, and various forms of leakage. The remedy in every case is obvious—coils for all wave lengths below 500 metres should

be wound wit# No. 26 d.c.c. wire, or even thicker. The Earth The earth is more often at fault than the aerial. In both cases all connections should be well soldered to reduce the resistance present in all Joints. The earth should consist of a couple of copper plates buried in damp earth two feet below the surface of the ground, a roll of wire netting, or (even better) a long strip of copper tape placed directly underneath the aerial. The great thing is to keep as large an area as possible in the soil. Leakage in wireless sets may be direct or indirect. In the former case the panel itself is leaky, and current escapes across the surface. In the latter, there is leakage by capacity, by the condensor effect set up between two wires or components mounted too near each other. Phones Lastly, always buy the best phones you can afford. Remember that cheap head phones often turn out to be very expensive in the end, while a good pair will last for years. Soldering The first important factor for getting the best results frc\n a rfjpeiving set is soldered connections. Every point should be carefully cleaned, and then securely soldered. Aerial joints should be carefully soldered, and a

proper ground clamp installed. Tb are at least 22 contacts in a fi ve ’ v '”‘, set, which cannot even be sol<l L. r . Twenty of them are valve prong co* tacts, and the other two are the * tery switch and the rheostat. any one of these will be a source of noise. Many valves h solder (lead alloys) on their prongs. This solder rubs off on to socket contacts, oxidises, and niaK high-resistance noisy connection. _ battery switch is often liable to up” after continued switching, must be cleaned. The same with rheostat. A dirty switch or rneo causes noise in a receiving set.