March Meeting: Modeling Jim’s HF Antenna

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At the Chelsea Amateur Radio Club we try not to let you down. Last month (February, 2024) we introduced you to the EZNEC antenna modeling software. Our plan for the March meeting (March 12, 2024) is to use either EZNEC or 4NEC2 to model and simulate Jim Grissom’s (KD8RFW) back yard HF trapped vertical antenna. We have not done it yet so this will be a learning exercise but we anticipate success.

While the dimensions of Jim’s Hustler 4-BTV antenna are well documented, the innards of the traps are likely NOT available. However, we anticipate being able to design traps for the simulation model that emulate the antenna performance.

In addition, before the meeting, we will make detailed vector impedance sweeps of the antenna as seen from the transmitter antenna output port. This will give us something substantial to compare the antenna modeling and simulation results against.

It is not yet known whether we will be doing our work in EZNEC or 4NEC2. However we can tell you that there is almost no comparative information on the two so this will also be a learning exercise in that respect as well. However, we can tell you what we have learned to this point concerning the differences between the two.

As a side note, there is another antenna modeling program that this author has not used. It is MININEC, developed by Rockway and Logan. This is an alternative method-of-moments program, developed specifically to run on small desk-top PCs.

First Glance Differences Between EZNEC and 4NEC2:

  • The engine under the hood (NEC) is identical for both. The engine was developed by Lawrence Livermore National Laboratory.
  • The differences between EZNEC and 4NEC2 lie in the graphical interface.
    • In theory, the two have the same capabilities.
    • However, the 4NEC2 graphical user interface offers
      • User defined variables–enables the user to define an antenna in terms of dimensions so that dependencies will track a single variable.
      • optimization capabilities.
  • Both are free.
  • EZNEC is the clear choice for those who are learning the basics of antenna modeling.
    • Primarily because EZNEC has an auto-segment menu pick that radically lightens the load on your skull when you bash it against the wall while trying to figure things out. This is a very important and valuable tool that all skill levels can benefit from.
    • This is because the GUI has fewer things to learn.
    • It is MUCH easier for tutorials to describe step-by-step actions to be taken with EZNEC because of its abbreviated nature.
    • Also, for those who are doing a one-time antenna project.
  • 4NEC2 is the clear choice for those doing an iterative project. The ability to define user variables greatly enhances the ability to change the dimensions of an antenna

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