A GOOD CATWHISKER

Radio Record, Volume I, Issue 13, 14 October 1927, Page 3

A GOOD CATWHISKER

TIPS FOR CRYSTAL, USiRS. Users of the catwhisker type of crystal detector know how frequently adjustment has to le made, due to the tendency of the whisker to jump from a good spot, owing to a slight jar or vibration. The slight shocks caused by tuning adjustments (says "N.A.T." in the Melbourne ‘"Listener-in") are often quite suificient to move the point of the wire, especially om a smoothsurfaced crystal of the galena type. , The amount of attention bestowed | on the crystal detector can be considerably reduced if it is placed on a shelf just above the wireless bench or on a separate table not too far away. | ‘Che connections between the detector and set are best made with flexible wire, as with rigid wire atiy movement at one end will be transmitted to the other, and any advantage from isolating the detector will be lost.

Use Flex Wire. Having obiained a piece of flexible wire of the required length-such as is used for electric iron or radiator ex-teusions-untwist it and make the connection with separate lengths. We know that we have been told not to do the wiring of a set with flexible Wire, owing to the capacity between the five strands; but for a short length such as this no ill-effects whatever will be. noticed. | For Heavy Yibration. If the set is situated in the neighbourhood of heavy traffic, such as 'trains, etc., the vibrations of the wall |may be too great to place th detector on a slielf. In such a case the following scheme has given excellent results. Obtain a disused inner tube of a motor tire and cut from it several strips about 5 inches wide by 18 inclies long. Now fold these strips of rub-ber-not too tightly-into cushions, and place one under each teble leg. The cushions will damp the vibrations

received from the floor. Saves the Good Spots. These precautions will save a lot of time and annoyance, as it will generally be found that one setting of the detector will suffice for a considerable period, the good "spots" not wearing out as quickly as many suppose. It is interesting to note that the rubber cushion is more efficient when placed under the table leg than une der the detector itself This is bee cause of a smaller moment of vibration being present in the former case. The effect is seen when a lon_ stick’ is held in the hand and swung through the are of a circle. The cnd near the hand moves through a relatively short’ space compared with the far end of the stick. So it is with the table leg. If we absorb the vibrations at the bottom of the leg there is much less trouble to overcome than if we attempted to de so after they had been amplified by travelling up the leg,