Such an aerial will serve well for transmitting purposes, but is too short for receiving very long distances. If the amateur desires to pick up long distance messages he must employ two aerials, a short one for transmitting and a long one for receiving. If it is desirable to use the long aerial for both transmitting and receiving its wave length may be brought down to 200 meters or under, while transmitting by placing a large glass plate condenser of the proper capacity in series with the aerial. It may be short-circuited with a suitable switch when receiving.
The law also says that the transmitting wave must be pure, and must be sharply tuned, which means that the wave must be of one length and not, as is very often the case, composed of two or more waves of different lengths.
In order to comply with this restriction, the use of an oscillation helix or loosely coupled helix is necessary. A rotary or quenched gap is also necessary in place of the ordinary spark gap.
The construction of all three of these instruments is described farther on.
How to Obtain a License.—In order to obtain a license send to the nearest Radio Inspector; Radio Inspectors are stationed at the Custom Houses at the following cities: Boston, Mass.; New York, N. Y.; Savannah, Ga.; Baltimore, Md.; Cleveland, Ohio; Chicago, Ill.; Seattle, Wash.; New Orleans, La.; San Francisco, Cal.; and obtain a copy of The Wireless Law, 8-6412, The Regulations Governing Radio Communication, The Berlin International Radio-telegraphic Convention, and the necessary Application Forms.
Look over the Wireless Law, the Regulations and the Berlin Convention pamphlet, then fill out Form 756. This is an application for an operator's license.
Fig. 150. Receiving Outfit Consisting of Receiving Transformer, Fixed Condenser and Detector.
If the amateur is not already in possession of a certificate of skill as an operator it will be necessary to find out, from the commandant at the nearest one of the stations, listed on page 4 of the Regulations as being the places where examinations are given, on what days the examinations are held. If the amateur is able to pass the examination, an operator's license will be issued. Then fill out Form 757 and forward it to the Radio Inspector. If he thinks your station conforms to the regulations without inspection the license will be issued; if not, the license will be issued after inspection.
There are no fees to pay in connection with securing any of the licenses.