ADDING DISTANCE

Sun (Auckland), Volume 1, Issue 16, 9 April 1927, Page 20

ADDING DISTANCE

IMPROVEMENTS TO THE ROBERTS ADVANTAGES OF RADIO FREQUENCY

BY the addition of a second stage of radio frequency amplification to a standard Roberts receiver, its selectivity and sensitivity are increased out of all proportion. With such a receiver it is possible to completely eliminate 3YA and, at the same time, to enjoy clear reception, from IYA, 4YA, and other New Zealand stations, while the tuning in this type of machine is simpler than the average three dial receiver. A Roberts with two stages of radio frequency amplification gives excellent results on distant stations, and in conjunction with a good aerial gives consistent reception from American Pacific Coast stations.

- three, as the extra radio frequency stage * is the same as the subsequent one, except that in the former case the grid - return wire goes straight to the fila- » ment, whereas in the reflexed stage it ; goes to the C battery and transformer I and then to the filament. The grid re- ; turn should go to the negative filament . between the A battery negative and * rheostat as shown under Ain diagram. It has been found in remote cases that if the return is made as shown at B, neutralisation is easier, hut generally the first method is much to be preferred, j in fact most sets will not work with * connection B. Neutralisation. It is essential that both tubes should r be correctly neutralised if the best re- * suits are to be had. Neutralising has I been dealt with fully in these columns, * so that the instructions will be brief.

The addition of a second radio frequency stage can be effected simply and without any very great expense. The following parts are required:— One Roberts unit less ticker coil, one variable condenser to suit same, one .005 fixed condenser, one 30 ohm fixed rheostat, ome 30 ohm rheostat, one neutralising condenser, one UX socket, nr UVI99 socket, one UXI99 tube, or UVI99 tube, one panel, see text. Apparatus Arrangement. The first thing that confronts the set builder is how is the unit going to be installed? Probably the best and most economical method, is to carefully unscrew the apparatus from present panel, unsolder wires, and leaving everything in position take off panel. Now procure a panel about nine inches longer than the present one, and using the old panel as a template for drill holes for

♦ he apparatus, leaving the extra line inches of panel projecting from the left of baseboard. On the panel extension mount the aerial coupler condenser, aerial switch, and 30 ohm rheostat. A piece of wood to form the base board for the panel extension should now be fitted, a strap being screwed to the old base to give it the required strength. The aerial coupler and switch should now be removed from its present position, and placed on the left side of panel.’ The new unit, together with its condenser, should now be placed in the position occupied by the aerial coupler. The set is now ready to wire. Wiring. The wiring offers no difficulties to the man who has built a Roberts two or

Tune in a loud station such as Dunedin, and adjust dials for best results. Turn out first tube by means of rheostat, and if 4YA can still be heard, adjust dials for greater volume. Next move neutralising condenser until signals disappear or are very weak. A position of the neutrality condenser should be reached that turning it either in or out makes the signals stronger; the first tube is then neutralised. The second tube is best neutralised tuning in a low wave length station such as 2GB or 2BL, Sydney. Then, with the set slightly oscillating there should be no click when the second dial comes in tune, if there is, neutraliser should be adjusted until there is no click, but only a slight rushing noise.