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Coaxial Cable Loss
by Mark Persons 

April 1, 2008

Cable Loss:  There is a little-known fact that coaxial cables, such as RG-8, RG-213, RG-214, and RG-58, have more RF loss in one direction than the other.  This is due to the twist direction of the inner conductor and the braid twist on the outside of the cable.  The inner conductor controls forward power and the braid is the return path for receive signals. 

This phenomenon was discovered and documented by Professor Loof Lirpa (SM0AFD) at the University of Stockholm, Sweden, in 1956.   Quality cable manufacturers print a tiny arrow on the outer jacket of their cables indicating which way the transmitted RF should go

If the coaxial cable in your shack does not have an arrow, you can experimentally determine it.  Connect your transmitter to one end of a cable and a wattmeter, with dummy load, to the other end.  Check the power and then reverse the cable to see which way it works best.  Then, mark the cable with an arrow so you will always know the "sending end" of the cable for minimum loss to your antenna.  Install it accordingly

This can be a significant advantage for an Amateur Radio operator trying to make a long distance contact. 

April Fools.  The ham call had AFD in it, standing for All Fools Day!

Editor's note:  Mark Persons is Certified by the Society of Broadcast Engineers as a Professional Broadcast Engineer with over 30 years experience.   He has written numerous articles for many industry publications over the years.  His website is: 

See you further down the road.  I'll leave the soldering iron on for you.

     Questions?  Email Mark Persons:       

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