THE WIRELESS WORLD.

Otago Daily Times, Issue 20501, 31 August 1928, Page 5

THE WIRELESS WORLD.

NOTES AND RECORDS,

By Magna Vox.

Items of local interest are invited by ■‘Magna Vos’' for publication > in t..is column It is necessary that such matter should reach this office by Tuesday of each neck for insertion on the following Friday.

ANSWERS TO CORRESPONDENTS. “ Noisv,” Palmerston.—l should think the paragraph entitled “Noisy Reception ” in this column would cover your query. “D. X.,” St. Clair. —In tuning your shortwave set, you will simplify matters considerably by using a dial of higher ratio than the one you are at present using- A variable condenser ot .0001 capacity is frequently used to facilitate tuning, but if this is altered tor one of larger capacity the number ot turns on the tuning coils would be altered, and an extra coil or two would also be necessary, “R D F.,” Roslyn—The window is probably the best place to bring your lead in. Flat, flexible strips of copper can be made to fit under the closed ■window and connect both aerial and earth to the set without boring holes or in any way interfering with the walls or roof of the house. Smtab.e strips can be purchased at most radio dealers, but it is cheaper to improvise . them.

NOISY RECEPTION,

If reception is marred by crackles and noise, and the set is suspected, disconnect the aerial, and if the poises are still present the receiver is the culprit. To test for faulty connections or loose joints, pound the table with the fist,, lightly, and listen. If the noise is affected, carefully touch around the internal wiring points, wobble the valves in their sockets, listening all the time. This will locate bad connections. Clean , valve legs with glass** paper occasionally. If the trouble is nofc located, it may, be caused by the batteries, broken-down audio transformer winding, or numerous other things.

FITTING TERMINALS AND SOCKETS It is remarkable the number of amateur constructors who find difficulty in the fitting of terminals and valve sockets, particularly the latter. Yet the task is easy, and consists simply in drilling a plain hole at least one drill size larger than the clearing size of the screwed stem of the terminal or socket. The result is, of course, a very loose fit, so one must depend on two tightly-locked nuts for security. In the case of valve sockets, one nut is sufficient, as they are not subject to any twisting action tending to unscrew them. Now the advantages of this method are that it is easier and takes, less time to drill a plain hole too.large than to drill a tapping size and afterwards tap; and it matters very little if the hole is drilled obliquely (as happens usually with most home constructors). In the case of valve sockets, which require the greatest accuracy in fitting, if a hole is slightly out of truth, through the drill slipping, the looseness of fit allows the necessary lateral movement to bring the sockets into their true position, and a valve plugged in will keep them in place whilst tightening up the nuts.

FOE THE HOME CONSTRUCTOR

Wireless is such a simple matter nowa days that we have quite lost sight of the days when the building of a receiver was an undertaking of some magnitude. Components were to be had, it is true, but the I prices were alarming enough to make the enthusiast with a certain amount of workshop equipment wonder whether he could not make his own components; really make the whole receiver with his own hands, in fact. Take a look at your latest broad- ! casting receiver, and try to imagine your- ■ self setting out to make every detail of it : from the raw material. Coils you could ! manage all right; fixed condensers would j not present much difficulty. Items such as the ebonite panel and the terminals, of I course, would not be worth your while to ! attempt. If your workshop were really weU equipped, you might make a good job of the variable condensers. But you would ■ hardly be able to construct a satisfactory I variable condenser in a “kitchen work--1 shop ” with only a drill, a saw, and a few files to help you. As a matter of fact, i when you set out to make your bum comit is a great mistake to follow too slavishly the designs which you have in front of you. There is almost always “ another way round,” and with the exercise of a little ingenuity you can arrive at the same goal as the manufacturer by different means. Your component will possibly not look quite so smart, but you will have the satisfaction of having made it yourself, and there is no rea- . son why it should not function equally well. One of the most valuable assets of 1 the man who “ makes his own ” is his store of “scrap” material. Very often the material of this kind which is ready to hand will decided the manner in which a component is to.be made. Some small metal article, useless in itself, will form the nucleus, so to speak, round which the ! gadget cap be b-iit. But your scrap stuff j is not going to be of much use to you if | it is piled up together in a box. You will never find what you want at the right ; moment. If you have got a spare drawer to put the scrap in, you can store it in such a way that everything is always handy. Start by collecting all the small j cardboard boxes in which wireless componnets or other articles are packed. Put these in the drawer, without lids, using the. lids as boxes as well. Fit them in carefully till the bottom of the drawer is covered. Now you will have a place tor everything.

ADVANTAGES OF A WAVE-METER. Some kind of wave-meter should, in fact, be possessed by every owner of a receiver which is capable of picking up a number of stations. Not . only does it aid him in tuning his set exactly to the wave-length oi the station it is desired to receive, but it also assists him to identify transmissions picked up when searching casually. With the wave-meter the wave length of the station picked up can be measured more or less accurately, which will show that the transmission must emanate from one of a small group of stations using wave-lengths closely approximating to that recorded by the wavemeter. A slight knowledge of languages will then usually be sufficient to indicate the exact source of the transmission picked up. The simplest form of wavemetrr, but one which is accurate enough for all ordinary purposes, requires only a tuning coil, variable condenser, buzzer, battery, and switch for its construction. The coil and condenser are connected in parallel with each other, and the buzzer battery, and switch in series with each other—across the coil and condenser.

When the switch is closed the battery operates the buzzer, the necessary current flowing through the coil. This causes oscillations- to be se. up in the tuned circuit, consisting of coil and variable condenser, the frequency of these oscillations being the same as the natural frequency of the tuned circuit. By altering the inductance of the coil, or the capacity of the variable condenser, the frequency of the oscillations can be adjusted. Very feeble “wireless” waves are radiated from the coil when oscillatory currents are flowing through it, which can be detected by a receiving set in the vicinity, provided that the receiver is accurately tuned to the same frequency as the wave-meter. A wave-meter is of little, use, of; course, until it has been calibrated —that is, until a record has been made of the wave-lengths corresponding to various settings of the wave-meter condenser. To calibrate a wave-meter, various transmissions, of known origin, should be tuned in on the receiver in the usual way. Each time a station is tuned in to maximum strength the buzzer of the wave-meter should be set in operation and the wave-meter condenser adjusted until the “ buzz ” of the wavemeter is heard in the ’phones of the receiver with the greatest intensity. Ine reading oi the condenser dial on the wavemeter will then correspond to the wavelength of the station which has been tuned in- As the identity of this station is known, the actual wave-length corresponding to the wave-meter reading can be at once jotted down. This procedure is to be gone through with -as many stations as can be identified when a curve can be plotted out on squared paper, showing the relationship between the wave-meter readings and the wave lengths of the stations which have bem used for the calibration process. From this curye the wave-meter settings corresponding’to intermediate wave lengths can also

be seen. To use the wave-meter in order to tune the eet accurately to a station whose wave-length is known, the wavemeter condenser is first set to the reading corresponding to the wave-length of the desired station .and the wave-meter switch closed. All that _ remains to be done is to alter the tuning adjustments of the set until the wave-meter signals are picked up with the greatest intensity, when the wave-meter buzzer can be shut off and the station itself received. If a transmission from an unKnown station is picked up, and it is desired to identify the station, the procedure is as follows:—The station is tuned in as well as possible, and then the wave-meter switch is put in the “on ” position. The wave-meter is adjusted until the “ buzz ” in the ’phones is at its maximum strength, when the wave-length of the transmitting station is easily ascertained from the curve.