Fig. 12(a) shows an easy way to remember these formulas:
When the finger covers one letter, it always equals the other
two in the exact relationship. When one is under the other it
means one divided by the other. When one is beside the other,
one multiplied by the other.
The velocity of Radio waves is always the same. It is
186,000 miles per second, or 300,000,000 meters per second. (A
meter is very nearly equal to 39 inches.) The velocity of light
waves is exactly the same. The velocity of sound waves depends
on what the waves are traveling through, but when traveling
through air they travel about 1,100 feet a second. At any rate
you see that we generally know the value of v in the above
formulas, and since in Radio we always use the "Metric" system
of measurements instead of the English, you must memorize the
velocity of Radio waves as 300,000,000 meters per second, or as
300,000 kilometers per second. (A kilometer is equal to 1,000
meters. )
Fig. 12(a)
In most Radio work the value of the frequency generally
runs very high: the frequencies used by broadcasting stations
vary from 500,000 to 1,500,000 cycles per second. It is often
annoying to have to use such large numbers, so we use the term
"kilocycle" to mean 1,000 cycles. For example: 1,000,000 cycles
per second is the same as 1,000 kilocycles; 1,500,000 cycles is the
same as 1,500 kilocycles; 500,000 cycles is the same as 500 kilocycles,
and so on.
So, in the formulas, which we have given, if we let v (the
velocity of the waves) be expressed in kilometers, and the frequency
f be expressed in kilocycles per second, we can write
them as
l = 300,000 / f
f = 300,000 / l
Remember that h is in meters and f is in kilocycles.
Let us do a few simple problems in order to illustrate how
