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The "Dope" on Wavelengths and Kilocycles
// you are not familiar with the relation between wavelengths and kilocycles, here is the opportunity to get it into your head in a few minutes. The information is likely to come in handy from time to time.
r 1 M4E
TV
dry to ;
current radiated from the aerial of a broadcasting station is alternating in character: that is, instead of having always the same potential and the same polarity (like the current from a dry cell, for instance), it is constantly changing in these respects, building up from zero potential to a maximum, or "peak," of positive polarity, and then "collapsing" to zero and building up to a similar peak of negative polarity. Such a current is represented in the accompanying diagram. It alternates very rapidly — at radio frequency, as it is called. A .cycle is a complete reversal of alternating current from a positive peak down through zero to the CK-— WA— -in
. . , LENGTH
negative peak and up through zero again to the next positive peak.
The number of cycles per second is called the frequency.
The physical distance between two successive peaks of the same polarity is called the wavelength, generally measured in meters. These waves travel through space at the speed of light — 186,000 miles a second or 300,000,000 meters a second. Now, if a wave makes 1,000,000 complete reversals a second (that is, has a frequency of 1,000,000 cycles, or, i ,000 kilocycles], it will make one complete reversal in
of a second; and in
of a second, any given peak (being part of a wave always traveling at
i ,000,000 i ,000,000
the rate of 300,000,000 meters a second) will move through space a distance of exactly 300 meters. A station transmitting with this i,ooo-kilocycle wave, then, is said to be sending "on 300 meters." Here is the equation for changing wavelength to kilocycles and vice versa:
300,000,000
no. of kilocycles x i ,000 = , .. .
' wavelength in meters
For example, if a certain wavelength is 400 meters,
300,000,000
no. ot kilocycles x 1,000 = = 750,000, or
400
no. of kilocycles = — — , that is, 750. (See table below). 1,000
The following tables give the frequency in kilocycles for various wavelengths:
FREQUENCY IN KILOCYCLES
I,5OO ],OOO 750 600 5OO 429
375
WAVELENGTH IN METERS
2OO 3OO 400 500 600 70O 800
FREQUENCY IN KILOCYCLES
333 300 200
150
1OO
75 60
30
WAVELENGTH IN METERS
QOO I.OOO 1,500 2.OOO 3.OOO 4,OOO
5,000
10,000
To check up a certain wavelength with its corresponding frequency, multiply the frequency (kilocycles x 1000, because one kilocycle equals 1000 cycles) by the wavelength. The result should be 300,000,000.