[TowerTalk] Re: TopBand: Re: Sloped Beverage Terminations

Wed, 22 Oct 1997 10:50:01 +0000

> From:          "Charles H. Harpole" <harpole@pegasus.cc.ucf.edu>

> 1.  just how long should it be (not in wavelengths, not in meters, but in
> gud ole American FEET) for 160 meters????

As long as you can make it, but anything over 500 feet ispretty much 
a waste of good wire if you have properly terminated and installed 
the antenna. That's because of the loss along the wire and the way 
the pattern is formed.  

> 2. what should be on the far end?  a carbon resistor?  or what? and of
> what wattage value?  and of what resistance value?

Any wattage, any carbon or metal film will work on 160. The optimum 
resistance value will be around 300-600 ohms, depending on the wire 
size, the environment around the antenna, and the ground system 
resistance. You'll see little difference if you make a termination 
error on a long antenna, because the long low wire self-terminates 
itself from the losses along the wire. (If the wire has six dB one 
way loss, typical for a 500 ft Beverage, the F/B ratio will be at 
least 6 dB with NO termination at all!)  

The shorter the wire, and the fussier you are, the more critical it 
is to get termination correct. Even the wrong termination does not 
hurt the system too much however, unless you have a lot of noise in 
the null direction.

Contrary to claims, measuring the antenna impedance at the antenna 
input on only ONE or two fixed frequencies does not work. The only 
exception is if you walk along and measure the antenna with a RF volt 
or RF milliampere meter (or if you find the lowest impedance 
frequency and highest impedance frequency and find the geometric mean 
value of those two impedances, and use that as the termination 
value).

73, Tom W8JI

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