Page:Popular Science Monthly Volume 88.djvu/655

 What Radio Readers Want to Know

��A Tikker Receiver and How it Works

C. M., Indianapolis, Intl., inquires:

Q. I should like some information concerning the "tikker" for the reception of undamped oscillations. I have heard considerable regarding continuous waves but so far have not been able to ascertain just how a tikker is constructed.

A. However constructed, the tikker is nothing more than a circuit interrupter arranged to open and close some portion of the receiving tuner circuits at a rate of 200 to 500 times a second. The original Poulsen tikker consisted of two light gold wires, one of which was attached to the vibrating member of an ordinary buzzer which, when set in operation, interrupted the circuit from the secondary winding of the receiving tuner to the telephones. At a later date another form of tikker was devised which consisted of a toothed wheel driven by a small motor and in contact with a brush.

The very latest type of tikker is known as a "slipping-contact detector." Of simple con- struction, it comprises merely a grooved wheel (with a perfectly smooth surface) rotated at a speed of say 1000 revolutions per minute. A small piece of thin steel wire is placed in light contact with the groove. The constant gripping and slipping of the wire during rotation causes a variation of the accumulated energy in the tele- phone condenser, thus setting up audible pulses of current in the telephone circuit.

The tikker, regardless of the type of construc- tion, occupies the same position in the secondary circuit of the receiving tuner as the crystal de- tector, but generally the secondary winding is constructed of Litzendraht to give a circuit having a minimum value of damping.

Range; Aerials; Quenched-Gap

D. P. D., Limon, Colo., asks:

Q. I. Will an aerial 100 ft. in length by 50 ft. in height be satisfactory for receiving messages from coast stations with 1000 to 1500 miles of mountainous country intervening? The local conditions for this work are good, since there are no high buildings or hills in the immediate vicinity. This aerial will have an altitude of 56(K) ft. above the sea level. Will I be able to receive ship stations with it?

A. I. If receiving apparatus of the vacuum- valve amplifier type is installed little difficulty should be experienced in receiving signals from the coast stations during the night hours.

Q. 2. Docs a series condenser cut down the sending distance of a transmitting set?

��A. 2. Speaking generally, it has the effect of cutting down the flow of current in the antenna system and therefore reduces the range. The insertion of a series condenser generally has the effect of increasing the total resistance of the antenna system.

Q. 3. Will an aerial 50 ft. in length by 40 ft. in height, composed of 4 wires spaced 3 ft. apart, be satisfactory for transmitting 100 miles using a. I. k. w. closed-core transformer and a rotary spark-gap?

A. 3. It will be rather difficult to consume the full output of this transformer at a wavelength of 200 meters because the capacity of the con- denser cannot exceed o.oi mfd. If the receiving station is fitted with suitable apparatus you will experience little difficulty in covering the desired distance at nighttime. During the daylight hours we should prefer a 2 k. w. or 5 k. w. transmitting set operated at an increased wave- length.

Q. 4. Which is considered the more efficient, a rotary-gap or a quenched-gap when the neces- sary high potential is obtained from the i k. w. transformer?

A. 4. The quenched-gap may be made the more efficient electrically, provided the trans- mitting apparatus is harmoniously designed throughout. A well-designed quenched-gap transmitter has a specially constructed motor generator and transformer. The range of the average amateur station will be increased by the use of a quenched-gap provided certain pre- cautions in the design of the apparatus are observed. For example, the oscillation trans- former should be so constructed that the in- ductance value of the primary and secondary windings can be regulated inch by inch. Like- wise the degree of coupling between the primary and secondary windings must be very closely adjustable.

The potential of the transformer requires careful regulation. In motor generator sets this is accomplished by means of the generator field rheostat, but where the energy is taken direct from the city mains it may be necessary to supply a transformer having variable tap-olTs in the secondary winding, in order that the cor- rect value of voltage may be obtained. In addi- tion, the high potential transformer must be one that possesses considerable magnetic leakage. If of the closed-core type, it should be fitted with a magnetic leakage gap. The open-core trans- former naturally possesses this characteristic. If you are not wholly familiar with the design and requirements of the quenched-gap dis- charger, the rotary-gap is recommended on ac- count of its simplicity, easy construction, and permanence of adjustment.

��627

�� �