SHORT-WAVE HINTS

Radio Record, Volume I, Issue 9, 16 September 1927, Page 14

SHORT-WAVE HINTS

Jn opetating a short wave set there are a nuwuber of pomts to be considered in addition to those common to both broadcast and the short waye. ‘Ihe folsowing hints are giyen as the result of practical experience, and may be of assistance to readers who are starting out on short-wave reception. _ Keep detector filament voltage as low -as possible. ‘his makes for yquict working and smooth oscillation. ‘The plate voltage must also be kept down, and probably from 20 to 80 volts HT will give satisfactory results. Very often better results are obtained by discarding the earth connection. In most circuits it is then necessary to connect the A battery side of the secondary tuning coil to the earth terminal. If the set shows any tendency to squea: when off oscillation point, try lowering filament voltage with the rheostat and also try a larger erid con--denser. The radio choke 1s not at all critical. -‘Megohm" "as used half a dozen, some elaborately wound on rest-tubes, | with 100, 150, and 200 turns, but 100° turns of 30’s roughly wound on an empty cotton spool with a small centre, answers as well as any. Where plug-in coils are used, the secondary condenser should be small in capacity, and may be made so by removing plates from a variable condenser until only five are left. This spreads out the stations on the dial and makes tuning less critical. There is no need to shorten a 100ft. aerial for short-wave reception, at! a greater length than this is said to be quite suitable. Loose aerial coupling and "ight rescfion coupling are usually best. For the guidance of those contemplating the construction of a set using movable plug-in coils, the following are approximately the three sets required to cover the range from 20 to 100 metres

with a smali secondary condenser as mentioned above:No. of Turns.

In houses with an alternating current lighting supply there is sometimes trouble in getting rid of the a.c. hum, and working with an earth connection is sometimes impossible in such a case. The hum has been removed in a particular case by placing a metal plate four or five inches square a few inches above the detector valve in a horizontal position and connecting the plate to ground by means of a thin wire. Other cures must be sought to overcome individual troubles of this kind, Switching the a.c. supply off is sometiines feasible in the daytime,

Pri, Sec. Reac. Metres 8 15 6 50-106 3 8 6 30-55 3 4 4-6 90-35