Open main menu

Page:Popular Science Monthly Volume 89.djvu/639

This page needs to be proofread.

Popular Science Monthly


��ground and also with the aerial, in scries with a hot-wire amnietcr. The secondary should then be adjusted until the maximum radiation is obtained. The aerial and ground siiould then be dis- connected, the condenser increased by one plate and the [)rimary again tuned to 200 meters. The secondary is again connected and adjusted for maximum radiation. This should be continued until the condenser is all in use. A table must be made with spaces for entries of each set of adjustments, and the set finally adjusted according to the combination which gives the highest radiation.

The adjustment marked X would be used, according to the table, since it gives maximum radiation current. In receiving, I have noticed that the chief trouble is interference. The ability to tune out one station and still hear another whose wave is nearly the same as the first, is a coveted ideal, especially since all the amateurs are on one wave, all the commercials on another, etc. A considerable advance in sharp tuning comes with the use of an audion-detector, since with this type of detector the operator must tune sharply if he wishes to hear anything at all. Another useful way of obtaining sharp tuning is by inserting a variable condenser in series with the aerial. By using large induc- tance in the primary and small series capacity, it is often possible to eliminate much local interference and still hear the desired station readably, although jierhaps not as loud as with the straight primary.

If a loose coupler is handled intelligent- ly, and the coupling between its coils is adjusted carefully, it will get rid of a lot of interference. A small condenser placed in shunt with the loose coupler secondary is always of assistance on the longer waves, such as those from 600 or 1,000 meters up. A sample table is shown in Fig. 4.

Many amateurs pay too little atten- tion to their ground connection. It is fully as important as the aerial. A ground which I have been using for over a year with the best of results is made of a */iG-in. sheet of copper, 4 by 6 ft., buried 10 ft. underground. Connection is made to this sheet by a

��No. 4 bare copper wire. This size wire is required by the Fire Underwriters, for both lead-in and ground-lead, and besides satisfying their retiuiremcnts, it is a help towards good transmitting results on account of its high conducti%'ity.

Many of the aerials seen as one goes through the city are not constructed with any idea of what their wavelength will be, or of which type of aerial is best

��Fig. 4



� �Warr

� � �Primarv


� �I.tnilh






�200 M.






� � �5- ■■



� � � �6- ■■



� � � �/-




� � �8- '■




� � �9- ■'




� � �10- ■•




� � �11- ••




� � �12- •■

� �6


��for the work desired, etc. For 200- meter work, the "T" type aerial is probably the best. It can be made almost double the length of an "L" aerial having the same wavelength, thus giving increased aerial capacity. A three-wire "T" type aerial 100 ft. long, not too high, has a fundamental wavelength which will be about right when used with sufficient oscillation- transformer secondar>' to bring the emitted wave up to 200 meters. Enough secondary may be used to insure good transference from the closed to the open circuits with an aerial of this kind. The wires should be spaced 3 or 4 ft. apart.

If an amateur's wireless set is given careful study in its design and careful work in its tuning and adjustment, there is no reason why, with operators of ^ by I K.W. input it should not do the long distance work that is being achieved by the few operators who have given their outfits careful study.

��Removing Old Putty from a Window- Pane with a Hot Iron

A HOT soldering or other iron run over old putty will soften it so that its rcmo%'al can be easily accomplished with a knife or chisel. Care should be exercised that the glass is not heated enough to cause it to crack.

�� �