Glossary of Wireless Terms

Radio Record, Volume II, Issue 16, 2 November 1928, Page 29

Glossary of Wireless Terms

This instalment concludes the glossary of wireless terms quoted from the "Listener’s Guide."

WAVE-LENGTH.-Although a station fs known by a designated wavelength it actually uses more than one. For instance we speak of a wavelength of 371 metres: but that is the mean or principal one of a group or band of wavelengths actually used. No broadcasting station can transmit on one wavelength. The tuning equipment of the transmitter must be adjusted to permit: of all or nearly all the frequencies employed in musical sounds to be transmitted. , That means that the radiated energy of a station must swing at least 5000 cycles above and 5000 cycles below the central frequency of the band. There is a definite and fixed relation between frequency and wavelength; the frequency is the number of eycles in a second or the number of times the alternating or vibrating energy of the system varies in a second. Thus if the alternations, vibrations or oscillations in a second amount to 50 as in electric light systems, or 600,000 as in a wireless transmitter, the frequency is known as 50 eycles per second or 600,000 cycles per second respectively. In the latter case the inconveniently long number is shortened to 600. kilocycles. (or 600 K.C.)-kilo- cycles meaning "thousands of cycles. The wavelength is the distance between corresponding points on two adjacent cycles of change or waves-the crests of the waves for example. As the velocity of radiation is constant at about 300,000.000 metres per second, the wave-length can be ascertained by dividing the frequency into the velocity. Likewise. if the wavelength is known the frequency ean be calculated by dividing the wavelength into the velocity. The frequency or wavelength of a transmitter can be measured by an‘ instrument called a wavemeter. Such an instrument. called a

meter. Such an instrument is a very important item of equipment at every station so that the engineers may observe frequently if their transmissions are on the correct wavelength. Therefore: (1) Wavelength equals velocity divided by frequency. (2) Frequeney equals velocity divided by wavelength. For example. to ascertain the frequency of a wave-length of 400 metres, frequency equals 300,000.000/400; results, 750.000 ner second. WAVE-METER.-A calibrated tuned cireuit which radiates, either by means of a buzzer or an oscillating valve (known respectively as a Buzzer, Valve-meter and Heterodyne Wave-meter) oscillations of a known frequency or wavelength. When set in action at a predetermined frequency, the receiving set may be tuned to that frequency, merely by adjustment to receive the oscillations of a wave-meter. On the other hand the wave-meter may be used to pick up signals by being placed in close proximity to a receiver and under these conditions the wavelength of the received signals mey be measured. WAVE-TRAP.-An alternative term for an interference eliminator, commonly employed for eliminating interference from a "local" station. The trap is adjusted to the frequency of the signals it is desired to tune out, and absorbs them by bynassing them to earth so that the desired signals can be received without interference from transmissions on a close wavelength. A slight loss of signal strength may result if the design of the wave-trap is such that a nearby powerful transmitter is to be eut out. For ordinary purposes of clearing up selectivity a well-designed wave-trap is a'very satisfactory piece of apparatus.