[TowerTalk] Inverted L for 160 meters

Tim Cotton, N4UM N4UM at bellsouth.net
Wed Oct 17 19:17:29 EDT 2007


The 165-175 foot length (longer than a quarter wave) raises the radiation 
resistance of the antenna to somewhere close to 50 ohms but, at the same 
time increases the inductive reactance.  The capacitor is used to cancel the 
inductive reactance when the total length goes beyond a quarter wavelength.

I use the same technique by making my "quarter wave verticals" longer than a 
quarter wave to bring their radiation resistance up to 50 ohms and then I 
tune out the additional inductive reactance by using series capacitance.  I 
live in a salt water environment and do not like using  expensive variable 
capacitors that are exposed to the elements.  I use pieces of coax as a 
simple inexpensive substitute for variable capacitors.  RG-8 runs about 30 
pf per foot.  I "tune" the coax capacitor with wire cutters and seal the 
exposed end with epoxy when I get the length right.  The trick is not to 
snip too much off at one time!

Tim, N4UM 

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