> 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
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search
|