DARA (you know, Hamvention) TNG is looking for projects. Thursday, I will be proposing building and characterizing a vertically-polarized 1 wavelength on a side reentrant rhombic.

Since in doing the presentation I want to show how a Rhombic gets its fabulous gain, I need to find out gains of various long wires, especially integer wave length wires, 1, 2, and four wavelengths long.

  • $\begingroup$ Hello Earl, and welcome to hamSE! It sounds like your Rhombic will be turned on its side, instead of being parallel with the earth. Can you edit your post (or add a picture, etc.) to clarify this design? I suggest you model this in EZNEC or another antenna modeling program. $\endgroup$ – Mike Waters Jan 3 '18 at 2:04

A 1 wavelength long wire has a 2.75 dBi free space gain, 2 wavelengths is 4.75 dBi and 4 wavelengths is 6.75 dBi.

I don't have the formulas at the top of my head to support this data. I am referencing Figure 1 in Chapter 13 of the 20th edition of the ARRL Antenna Book.

In a paper I have from Cebik in antenneX Online Magazine, he shows 2.99, 4.81 and 6.98 dBi respectively.

These two sources show reasonable agreement. I would anticipate higher gain when the antenna is close to ground. If you need the formulas, indicate so in the comments and I will look them up for you.

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