4NEC2 taper schedule

Could any 4NEC2 gurus out there advise me how to set up a taper schedule in 4NEC2 for a yagi together with an associated symbol table to use to run the optimiser? Alternatively, could anyone provide example input files that I could play with? I have spent some time Googling for such info but haven’t managed to find anything. I am using 4NEC2 version 5.9.3

Thanks, Simon

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Simon, I’ll ask our resident NEC guru at the club if he knows.

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I’m not sure what do you mean with “taper schedule”.
But to optimise an antenna

  1. define the geometry and use variables (symbols) for coordinates and dimensions you want to optimize,
  2. use fixed values for the other coordinates and dimensions,
  3. define the symbols and give them reasonable values to start with,
  4. save the input file,
  5. start “Calculate” - “Start Optimizer”,
  6. in the optimizer window select the variables you want to optimize, set the frequency and weight factors for the outcome measures and
  7. hit Start.

May be you will optimize the length and position of the director of your 2 m yagi (only one director available). The yagi boom should go along x direction and the hight over ground (z direction) should be variable. X = 0 may define the position of the reflector.

Use the NEC editor (new).

In the tab “Symbols” edit
hog = 10.00 Comment: Hight over Ground, value 10.00 m
led = 1.00 Comment: length of dipole, value 1.00 m
dpos = 0.40 Comment: position of dipole, value 0.40 m (from reflector)

In the tab “Geometry” edit for the director
X1=dpos Y1=-led/2 Z1=hog X2=dpos Y2=led/2 Z2=hog (and add the other parameter values)

Edit the other tabs (if needed) and save the input file.

In the optimizer window mark “hog” and “led” to optimise these parameters, set Frequency = 145 and a weight for the goals e.g. SWR: 50 and Gain: 100.

Hit Start and the optimizer should run (if all the other parameters of the antenna model are ok).

Are these the informations you are looking for?

73, Ludwig


Hi Ludwig,

Thank you for taking the time to send an answer. I am reasonably comfortable using 4NEC2 to optimise a yagi with fixed diameter elements. However, what I need concerns the modelling of yagi elements having two or three different diameters ie the elements are tapered, from large to smaller diameter tubes. There is a specific tick-box in the 4NEC2 geometry definition tab “Use wire tapering” and it is how to use that that I am asking about.

73 Simon

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Hi Simon,

ok. What is the problem? So far as I see, there are 3 fields for tapering and a help for each field in the header.
What do you want to optimize?
Did you made a test using variables for these fields?

73, Ludwig

Hi Ludwig,

I’m afraid it is not obvious to me what values should be input into the L_Ratio, Rad-1 and Rad-2 columns. I have been trying to model elements with tapered diameters of 16mm,12mm and 10mm. Then I do not understand how to define the symbols for optimisation - defining symbols for the element position along the boom is simple enough, but how do you define the symbols for the individual tapered element lengths? My attempts to date fall over because the optimisation routine pulls the elements apart.



at first, sorry, I never optimized with tapering elements.

So far as I understand, the parameters are for:

  • the ratio of the “segment” length relative to the previous segment (equal length when 1.0),
  • radius for the first segment and
  • radius for the last segment.

I guess “segments” relates to the segments generated by the parameter “Segs”. So each segment has it’s own radius, from the largest to the smallest.

I guess also for a symmetric structure like a yagi you have to devide each element in two, one left from the boom and one right. So you get a symmetric tapering on both sides.

But you may taper in a different way, not using the option. Devide each Element in five pices, the middle part with 16 mm, the next parts on the left and right side with 12 mm and the outer parts with 10 mm. Than you may use a indepentant segmentation of each part.

73, Ludwig

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you may test something to find out the affects of tapering.
Edit one element with tapering and use parameters like supposed.
Make a simulation using a reasonable frequency.
Open the Geometry window (F3). Click on different places on the element. The local segment will be highlighted, you find the borders of the segment and in a small info window some parameters of the segment are shown, also the radius.

73, Ludwig

EZNEC (v6) users still have a less abstract view of e.g. NEC-2 segments and “Segment Tapering”, so one would probably have to become familiar with the terminology used by 4NEC2 first.

Each wire is divided into segments for analysis purposes. The NEC calculating engine assumes that the current has an essentially sinusoidal shape over the length of a segment, and that the currents of adjacent segments match at their junctions and some distance beyond. This makes the problem one of finding a finite number of impedances, currents, and field strength contributions. Some of the skill in modeling is in choosing the number of segments. EZNEC will choose for you (with its automatic segmentation feature) if you wish, but its choice will often not be best.

Segment Length Tapering
Note: The process of making an element from telescoping tubing is called tapering by some authors, and corrections for NEC-2’s inaccuracy in modeling these is sometimes called taper correction. EZNEC uses the term segment length tapering or segment tapering to refer to the process of stepping, or tapering, segment lengths, rather than diameters. (The process of correcting NEC-2 for steps in wire diameter is called stepped diameter correction.)

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Maybe someone in this user group can answer your question:

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Thanks Heinz :+1:

Unfortunately the group is full and won’t accept emails from unsubscribed members :slightly_frowning_face:


Strange, there was no official information about this.
Maybe G8HUL knows a little more or can even answer your question (unfortunately I don’t have an email address for Jeff), or you can ask the question in the EZNEC user group (EZNEC also uses NEC-2).

Edit: M0HAO is another well known contributor (email address on QRZ).

BTW, once you have registered with groups.io, you can easily apply for membership in a specific user group by clicking on it.

73 gl, Heinz