Page:Popular Science Monthly Volume 89.djvu/467

 What Radio Readers Want to Know

Announcement

Beginning with this issue, the Editors are extending the scope of the Questions and Answers Department so as to include a Radio Headers' Service Bureau. Answers to any questions you wish to ash us will be sent by mail directly to you. Queries of general interest, with their answers, will be published monthly in these pages.

This new service it furnished free to our readers. The questions will be answered by authorities in the branches concerned. Your inquiries may be on any topic related to wireless telegraphy or telephony.

The Editors suggest, however, that queries as to the wave-lengths of aerials and the working distance ranges of various senders and receivers be uriihhcld. These subjects have been explained so often that almost any desired informal'ion as to them may be found by reading over the earlier issues of the magazine.

What books to read, hoir to build apparatus, hou' to adjust it, and where to buy it, arc only a few of the things we can tell you. If we can help you, write to ws/

��A Simple Wireless Telephone

L. N. P., WaynesviUe, O., writes:

Q. I. Please state where I can obtain direc- tions to make a simple wireless telephone set that will transmit to a distance of one or two miles. I desire an apparatus that does not in- clude an arc gap or other expensive apparatus. Please give instructions for the construction of a simple set.

A. I. You are advised to purchase a copy of "Simple Wireless Telephones and How to Make Them," on sale by the Book Department of this magazine. The price is 25c per copy.

A very simple wireless telephone set for amateur purposes may be constructed in the following manner: If you are already in pos- session of a wireless telegraph transmitting set, you can take the high potential transformer and connect it directly to the terminals or the spark gap, the latter in turn being connected in scries with the antenna system. A microphone trans- mitter is connected in series with the earth lead for variation of the antenna current in accordance with the vibrations of the human voice. Due to the small capacity of the antenna the spark as- sumes the nature of an arc, and oscillations of an exceedingly high spark frequency flow in the antenna circuit. In fact they are of sufficient fre- quency to permit the transmission of the human voice. You should have no difficulty in covering a distance of one or two miles with this apparatus.

Receiving Long Waves M. M., Danville, Pa., inquires:

Q. I. What is the wave length of my aerial which is 140 feet in length, 35 feet in height, con- sisting of two copper wires on four foot spreaders. The lead-in wires are 25 feet in length.

A. I. The fundamental wave length is ap- pro.\imately 3IQ meters.

Q. 2. Please give the size and dimensions of a long wave length loose coupler to be used with this aerial.

��A. 2. The longest wave length used by any spark station is that of the Marconi Company at Glace Bay, which employs a frequency wave length of 8,125 meters. In the November, 1915, issue and the April, 1916, issue of this magazine, there are described the complete circuits for an oscillating audion detector which will permit loud response from stations using damped and undamped oscillations, and you would secure better results by constructing apparatus of this type rather than a simple inductively coupled receiving tuner. However for crystalline detectors the tuner may have the following dimensions: The secondary winding 6" in diameter, 12" in length, wound with No. 30 S. S. C. wire. It is intended to be shunted by a condenser of .0005 microfarads. The corresponding primary wind- ing is 7" in diameter, 12" in length, wound closely with No. 24 S. S. C. wire. The loading coil for the antenna circuit is 14" in length, 7" in diameter, wound with No. 22 S. S. C. wire.

Sending on Short Wave

W. D. H., Olathe, Kansas, writes:

Q. I. I have an aerial 50 feet in height, 200 feet in length, composed of a single wire. The lead-in is 35 feet in length and the ground lead 20 feet. Please advise how to construct a short wave condenser that will reduce the sending wave length to 200 meters. I use a 5 K. W. high potential transformer.

A. I. The fundamental wave length of your aerial is approximately 360 meters which is rather long to be operated at wave lengths of 200 meters. In fact a series condenser will just barely reduce the natural wave length to 200 meters and will not allow turns to be placed in the secondary winding of the oscillation transformer. You are advised to reduce the length of the aerial to 130 feet and then if possible attach the lead-in wire to the center of the flat top portion. With this connection you can send at the wave length of 200 meters without a series condenser.

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