Re: wire for random wire antenna using kx3

Posted by Don Wilhelm on Dec 18, 2018; 3:26am
URL: http://elecraft.85.s1.nabble.com/wire-for-random-wire-antenna-using-kx3-tp7647146p7647176.html

I am also a retired engineer, and I find that often it is quicker and
easier to put up an antenna cut to the "standard" formula (OK, I start a
bit longer than that), then check with an antenna analyzer and cut from
there.  Modeling is great if you can take into consideration all factors
such as height, ground quality, surrounding objects, etc. - but it is
difficult to consider all that in advance.

If your desire is to obtain the horizontal and vertical radiation
patterns, then modeling is the best way to do that.

If you want to cut only once, use the technique I had published in QST
Technical Correspondence May 2018.
Cut the radiator to 468/F(MHz) plus 5 or 10%.
Measure the radiator length and put it in position.   Then with your
antenna analyzer, measure the resonant frequency in MHz.  Now multiply
the actual frequency times the length to find a new "cutting factor"
(will be different than 468).  Divide that new 'cutting factor' by the
desired resonant frequency, and then trim the antenna to the new length
- put it up and it will work.

Remember that the resonant frequency is where the "X" component of the
antenna is zero - it may be the same as the lowest SWR, but not
necessarily so.

73,
Don W3FPR

On 12/17/2018 9:56 PM, Fred Jensen wrote:
> Yes, to each his own.  As a retired engineer, I relished the day I could
> forego all of the planning, research, design + review cycles, quality
> assurance reviews, prototype testing, test reviews, program management
> reviews, customer reviews and feedback, and 250K miles/year on United
> Airlines.  I model antennas with EZNEC4, I'm old and endurance flags
> some before the trial antenna is up.
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