Page:Popular Science Monthly Volume 88.djvu/656

 6^8

��Popular Science Monthly

��Induction from Streetcars

��F. M., Washington, Ind., writes:

Q. I am about to purchase certain wireless telegraphy instruments, but inasmuch as my receiving aerial will be located near a streetcar line and powerhouse I desire to know what effect these wares will have on the reception of signals?

A. Although you may expect to receive inter- fering sounds from these wires due to electro- static induction, they will not wholly prevent the reception of signals. If possible, place the receiving aerial at right angles to the power line.

Receiving-Tuner Doubts Cleared Up

W. B. H., Fresno, Cal., inquires:

Q. In the December, 191 5, issue you give cer- tain dimensions for an inductively-coupled re- ceiving tuner to cover a range of 1500 meters. The statement is made that the primary and secondary windings should be made of No. 28 B. & S. fage copper wire. To me this seems incor- rect. I cannot understand how the secondary voltage will be any different from that of the primary if the same size of wire is employed. Before commencing the construction of such a tuner I should like to have this matter cleared up.

A. It is perfectly feasible to cover the primary and secondary' of the receiving tuner with the same size of wire. For the average crystal de- tector it is customary in some forms of com- mercial apparatus to use No. 32 S. S. C. wire on the secondary. A step-up ratio of turns in an oscillation transformer does not necessarily mean a stepping up of voltage, since there are other factors which must be taken into considera- tion. Please understand that the actual wave- length to which the tuner described in the December, 1915, issue will be adjustable depends upon the capacity of the condenser in shunt to the secondary winding. With a secondary winding 5 ins. in length by 4J ins. in diameter, covered with No. 32 wire and shunted by a con- denser of o.ooi m.f. capacity, the tuner will be adjustable to wavelengths in the vicinity of 4000 meters.

Where to Place Receiving Aerials

R. P. C, Nineveh, N. Y., asks:

Q. I wish to construct an aerial 60' in height by 200' in length. Our buildings are surrounded by hills. In which location do you think I would achieve the better results for receiving purposes, namely, by suspension of the wires on 20' poles atop of the barns which are 40' in height, or by placing them on 60' poles upon the hill, which is 200' above the barns? Our elevation is 1145' above the sea level. Approximately over what distance may I expect to receive messages?

A. For general work we should prefer to erect

��the aerial on the hill, provided that the receiving apparatus can be housed in the immediate vicinity of the aerial. The actual distance over which messages may be received depends en- tirely upon the type of receiving apparatus in use. With the average amateur equipment fitted with a crystalline detector you should be enabled to copy messages at nighttime during the favorable months of the year from all com- mercial stations located on the Atlantic coast and Gulf. With an extremely sensitive long distance set, say one employing a regenerative receiving circuit in connection with the audion, you should experience no difficulty in receiving messages from the radio station located at Nauen, Germany.

A Receiving- Condenser for 1500-Meter Loose-Coupler

W. M. K., Windsor, Ont., inquires: , Q. I. I should like to put this department to trouble again by asking for information concern- ing the size of a receiving condenser for a 1500- meter loose-coupler. Approximately how many tinfoil sheets should be used and what are the required dimensions?

A. I. We assume that reference is made to the fixed condenser in shunt to the head tele- phones. Two sheets of tinfoil 30 ins. in length by 2h ins. in width, separated by a thin piece of paraffin paper and rolled up on circular form, will give a sufficient value of capacity for the average requirements. The variable condensers must be of the air dielectric type such as supplied by electrical supply houses advertising in the columns of this magazine.

Q. 2. Approximately over what distance can I receive with this set connected to an aerial 90 ft. in length and 50 ft. in height at both ends, keeping in mind that the tuner is adjustable to a wavelength of 1500 meters?

A. 2. During the nighttime this apparatus should be responsive to stations 1000 to 1200 miles distant. The daylight range is proble- matic.

Sustained Waves and Government License

H. W. D., Jr., Schnectady, N. Y., asks:

Q. I. May an amateur make use of a set responsive to an undamped wave?

A. I. There are no regulations governing the type of receiving apparatus employed at the amateur station. If an undamped oscillation transmitter were employed it would be necessary to secure a U. S. station license.

Q. 2. What is the fundamental wavelength of a four-wire aerial 120 ft. in length, 45 ft. in height at one end and 50 ft. at the other with a lead-in of 25 ft. placed at an angle of 70 degrees to the aerial?

A. 2. The natural wavelength of this antenna is approximately 320 meters.

�� �