Monday, March 21, 2011

Lesson 30: General Class Exam Course G9A

Here is lesson 30!  This lesson deals primarily with antenna feedlines, impedance, and SWR.  This lesson is fairly straight forward with no complicated formulas or concepts, but there are a few items you will need to memorize.  Those things are:

-The characteristic impedance of feedline most often used in amateur radio is 50 and 75 ohms.

-Flat ribbon TV type twin lead is 300 ohms.

-Attenuation is the reduction in signal strength expressed in dB.  When you see attenuation, think signal loss.

-RF feedline loss is most often expressed in dB per 100 feet.

-To find Standing Wave Ratio (SWR) when all the impedances are known, simply divide the larger impedance by the small impedance.  SWR is expressed with the larger number first with the second number always reduced to 1.  For instance: 4:1, 3:1, and 2:1.  It is not expressed 1:4, 1:3, 2:1.5, etc.

That's about it for this lesson.  As always, feel free to leave any comments, suggestions, or questions in the comments box!