Chapter 29

range of wave-lengths to transmit the necessary side-bands. Then the range is from 598 m. to 603 m.

In the case of the transmission of speech by radio we are interested in having no interference from other signals which are within 2000 cycles of the frequency of our radio-current no matter what their wave-lengths may be. The part of the wave-length range which must be kept clear from interfering signals becomes smaller the higher the frequency which is being modulated.

You can see that very few telephone messages can be sent in the long-wave-length part of the radio range and many more, although not very many after all, in the short wave-length part of the radio range. You can also see why it is desirable to keep amateurs in the short wave-length part of the range where more of them can transmit simultaneously without interfering with each other or with commercial radio stations.

There is another reason, too, for keeping amateurs to the shortest wave-lengths. Transmission of radio signals over short distances is best accomplished by short wave-lengths but over long distances by the longer wave-lengths. For trans-oceanic work the very longest wave-lengths are best. The "long-haul" stations, therefore, work in the frequency range immediately above 10,000 cycles a second and transmit with wave lengths of 30,000 m. and shorter.