SHORT-WAVE HINTS

Radio Record, Volume I, Issue 14, 21 October 1927, Page 12

SHORT-WAVE HINTS

"TQ SECURE OSCILLATION. It is often the case with a short wave receiver that when the grid circuit is tuned to some particular wave-length the set refuses to oscillate. Such an effect is produced when the aerial and the grid coils are tuned to the same frequency, To get over this, use a small two-point switch. Connect the aerial to the movable arm of the switch, and from the contact point to the aerial of the receiver. Then connect a fixed condenser with a capacity of 0.0002 imfd. across the points of the switch.

When the point where the set refuses to oscillate is reached, open the switch, and the fixed condenser will be placed in series with the aerial, thus shifting the ‘‘dead spot’? to some other frequency where it will not be troublesome. It is a common idea amongst many persons that on the short wave-lengths a correspondingly short aerial should be used. ‘This is not so, as experiments have proved. It was found that for five metre reception the longest aerial possible, but no earth connection, provfed to be the best possible method of pick-up. For reception on wave-lengths from 15 metres up to 100 metres an aerial with an overall length of 250 feet is ‘advisable. This will give a greater pickup of R.I*. currents.