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Radio Broadcast
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FIG. 8 The terminal initials of the transformers plainly indicate the principle involved in lining up the windings
CAST told how the wave range could be increased by means of added capacities. However, on many sets, greater efficiency and better results can be secured through a genuine load, that is, by means of inductance.
Such an inductance may be wound on a 4inch tube with 75 turns of No. 22 to No. 24 wire. If you care to take a little more trouble in winding the coil, it can be done in such a way as to take up less space for the same amount of effective inductance. This is accomplished by winding 44 turns of wire in a pyramid bank winding on the same size form. This means that the first layer will have 9 turns, and each succeeding layer one turn less.
In order to avoid, as far as possible, the dielectric losses which are apt to be present when shellac or some similar substance is employed as an adhesive, it is suggested that the coil be painted with collodium, which is obtainable from any druggist.*
Fig. 9 shows how this inductance is mounted beside the plate variometer, and in the same plane with the stationary windings. The coil should be located on the far side of the variometer, in order that it will have no inductive effect on the remainder of the set. The electrical position of this coil is in series with the secondary of the variocoupler, i.e., between the lower lead and the filament battery. Before the set will regenerate properly, it will in
This bit of advice appfies to any other type of coil, and it is worth following. — THE EDITOR.
some cases prove necessary to reverse the leads to the coil.
In many cases it is a good idea to provide a panel switch for cutting the extra coil in and out of the circuit. This is quite necessary when it is desired to receive amateur wavelengths (below 220 meters).
It will be observed that on short waves regeneration is effected by means of the tuned plate method, and on the longer waves, by a combination of tuned plate and tickler feedback to the grid circuit from the plate variometer to the coil. This arrangement gives adequate regeneration over the entire range.
A standard receiver employing this addition and using an aerial of average proportions, was found to have a wavelength range of from under 200 meters, to over 900 meters; and it could be made to oscillate, with little difficulty, on all waves.
Slightly different characteristics were noted on the short waves after the change was made, but results were every bit as good, and on waves over four hundred meters, a much better signal was obtained.
BUILDING YOUR OWN LAB
THIS month's suggestion for the growing workshop is a good hack-saw, accommodating different lengths of blades, costing from seventy-five cents to one dollar. A small assortment of blades should be bought at the