Text 10The origin of fairy tales.

       Many times the question, "What is a fairy tale?" has been asked. One has said: "The fairy tale is a poetic presentation of a spiritual truth." George MacDonald has answered: "Undine is a fairy tale." Mr. G. K. Chesterton has said: "A fairy tale is a tale told in a morbid age to the only remaining sane person, a child. A legend is a fairy tale told to men when men were sane." Some, scorning to reply, have treated the question as one similar to, "What poem do you consider best in the English language?" As there are many tales included here which do not contain a fairy, fairy tales here are taken to include tales which contain something fairy or extraordinary, the magic or the marvelous--fairies, elves, or trolls, speaking animals, trees, or a talkative Tin Soldier. The Myth proper and the Fable are both excluded here, while the pourquois tale, a myth development, and the Beast tale, a short-story fable development, are both included.

The origin of the word "fairy," as given by Thomas Keightley in his Fairy Mythology, and later in the Appendix of his Tales and Popular Fictions, is the Latin fatum, "to enchant." The word was derived directly from the French form of the root.

Text 11Radio transmitter design

Radio transmitter design is a complex topic which can be broken down into a series of smaller topics. A radio communication systemrequires twotuned circuitseach at thetransmitterandreceiver, all four tuned to the samefrequency. The transmitter is anelectronicdevicewhich, usually with the aid of anantenna, propagates anelectromagneticsignalsuch asradio,television, or othertelecommunications.

Design issues

The radio transmitter is one element of a radio system. As well as the perpetual constraints of budget and schedule common to any project, a radio transmitter design must consider multiple technical and regulatory factors. These include the frequency of operation, the type ofmodulation, the stability and purity of the resulting signal, the efficiency of power use, and the power level required to meet the system design objectives. High-power transmitters may have additional constraints with respect to radiation safety, generation of X-rays, and protection from high voltages. Typically a transmitter design includes generation of a carrier signal, optionally one or more frequency multiplication stages, a modulator, a power amplifier, and a filter and matching network to connect to an antenna. A very simple transmitter might contain only a continuously running oscillator coupled to some antenna system. More elaborate transmitters allow better control over the modulation of the emitted signal and improve the stability of the transmitted frequency. For example the Master Oscillator-Power Amplifier (MOPA) configuration inserts an amplifier stage between the oscillator and the antenna. This prevents changes in the loading presented by the antenna from altering the frequency of the oscillator.

Frequency synthesis

Fixed frequency systems

For a fixed frequencytransmitter one commonly used method is to use aresonantquartzcrystalin aCrystal oscillatorto fix the frequency. Where the frequency has to be variable, several options can be used.