Tid Bits

This page is for items you may not have known but would like to know.

Question:
What is the speed of light, and how is it important to radio?

Answer:
The speed of light can be remembered in meters as “300”. 300 million meters per second.

Radio waves travel at the speed of light and most radio antennas are designed at 1/4 of the wavelength of the radio frequency.

The formula for finding the length of a 1/4 wave antenna in inches is: 1/4wave=(300/frequency/4×39.37 ).

So a 1/4 wave antenna for a Citizen Band radio would work something like this:

300/27.185 (the frequency of channel 19) = 11.035 meters (hence the reason we call CB the “11 meter band“).

Then 11.035/4 = 2.758 (the 1/4 wave of 11.035 in meters).

Then 2.758 x 39.37 (convert from meters to inches) = 108.616 inches.

Have you ever seen those stainless steel whips on the pickups of the “CBers”? They are known as 102″ Stainless Steel Whips. Then when you add the 6″ spring, you have 108 inches! Ahah!

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Some frequencies 1/4 wave are too long to work in “inches“, so divide your answer by 12 to convert to “feet“. Or use the multiplier of 3.28084 instead of 39.37. So, a 3.5 Mhz 1/4 wave antenna would be: 300/3.5 = 85.714 meters. Then 85.714/4 = 21.428 meters (the 1/4 wave length). Then 21.428×3.28084 = 70.301 feet. Your typical 75 meter antenna would be around 66 feet long for a 1/4 wave.

It does not matter what the frequency is, this is the formula to answer the question of what is needed to have an antenna that resinates. Have Fun!