Wireless Telegraph Construction For Amateurs

by Alfred Powell Morgan

The relation between the thickness and the diameter is shown by the following: If the diaphragm of a receiver is increased in diameter, the tones will become more distinct, but if the increase is carried too far they will become indistinct and the only remedy is to thicken the diaphragm. Likewise if after clearness is secured the diaphragm is thickened so that the tones again become indistinct, the diameter must be increased.

Fig. 143. Grinding Tool.

The third objection is that such receivers are not carefully and properly adjusted. The adjustment is also a matter of experiment and is accomplished by comparison of the receiver in question with one which is known to be in a sensitive condition. The adjusting may be done by means of the tool shown in Fig. 143.

This tool is made from an ordinary file by grinding off the teeth on one side save for a distance of about 3/4 inch in the middle. The grinding may be done on an emery wheel. The part (a) is used for filing the pole pieces and thus making the distance between them and the diaphragm greater. The tool has the advantage over an ordinary file of permitting the poles to be filed without removal from the receiver and without grooving the diaphragm bed or the receiver case.

To lessen the distance between the poles and the diaphragm, lay the receiver bed downward on a piece of fine emery paper and rub with a circular scouring motion. If the emery paper is placed on a perfectly flat surface no trouble will be experienced in grinding the bed down evenly.

When filing the pole pieces rub with the same circular motion so as to grind off all sides evenly. Test from time to time by passing a straight edge over the bed in all directions while holding to the light and looking between the straight edge and the poles. In this manner the distance separating the diaphragm and the poles may be gauged and whether or not it is the same on all sides. Bear in mind that if the diaphragm is thin, the attraction of the permanent magnets will cause it to bend in towards the poles.

In case you have a pair of receivers built for wireless work, which appear to be in good condition but do not give their former results, the last thing to do is to tamper with the adjustment. The most common cause, when the tones are impaired, is dirt or dust accumulated on the poles or diaphragm and damping its vibration. The cap should be carefully unscrewed and the diaphragm examined to see if it is bent. If so, replace with a new one of the same size. Remove any dirt or filings, and if the diaphragm is rusty clean it by laying it on a flat surface and rubbing it with a piece of fine emery paper. Then give it a thin coat of colorless lacquer. Examine the magnets and pole pieces to see if they have become loosened and if so tighten them.

Or the trouble may be that the permanent magnets have lost part of their magnetism, and almost any receiver which has been in use for some length of time will bear having its magnets strengthened. If they are found to be weak they should be removed and remagnetized. This is accomplished by winding a coil of No. 18 B. S. gauge wire around them and sending a heavy direct current through for a few minutes.