TopBand: Inverted-L

[Bruce Lallathin]

At 11:21 AM 10/31/98 -0800, you wrote:

I plan to put up an Inverted-L for 160.  Do I need a balum?  Can I feed
it with ladder line?  Is the longer the better or should I stick to +/-
170 feet.
==================
Hello Russell,

FB. Whether you need a baluN or not will be determined on the quality of 
your RF ground at the feedpoint. Usually, with a minimal ground consisting 
of a couple quarter wave radials and maybe an 8' ground rod, depending on 
soil conductivity, you may match it directly with 50 ohm cable. The better 
your ground screen, more radials,,,the closer the feedpoint will be to about 
35 ohms. If you measure the feedpoint and find 50 ohms, then you can bet 
most of the power you send to the antenna will end up warming the worms and 
not being radiated....ground losses. As you add more radials, the losses go 
down and the antenna will really start to perform very well. At this point, 
close to 30 ohms or so you may want to put some sort of matching network. 
The easiest to do is to wind a torroid transformer like W2FMI suggests to 
take care of that. You will be amazed at how easy it is and how well it will 
work. 

Another way to do it is to elevate your radials as high as you can, but this 
usually means you will end up with more wire horizontal and less vertical. 
Depending on what you want to work with the inverted-L, this may not be all 
bad. I used this method on Rarotonga. The radials, about 20 of them were 
about 15' off the ground and the feedpoint was matched with a torroid. It 
was an effective antenna and fairly quick to get up and working. I forgot 
how long the radiator was. You will likely have to find the optimum length 
by cut and try anyway given your location. 

I've heard that by making the radiating wire slightly longer than a quarter 
wave length gets the high current point up the wire some and this is 
good...problem is you have to put a series cap in line to tune out the 
reactance. I found this to be too much hassle and opted for the torroid 
method. 

There are lots of reference materials available on this subject. Try ON4UN's 
Low Band DX'ing for starters. Also pickup W2FMI's publication of torroid 
transformers. 

Good luck with your projects. See you on 160!

73,
Bruce
AA8U  ZK1AAU  FP/AA8U  


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