Wednesday, January 21, 2015

3 Antennas Compared

Recently we discussed the comparative performance of 3 wire antennas, sized for 80 m, on 3.5 MHz and above. I used antenna modeling to compare the following antennas, all at 40 ft above rocky ground:
  • W8JI 110 ft dipole
  • Horizontal Loop of 287 ft
  • 133 ft Off-Center Fed Dipole

I found that the shapes of the radiation patterns vary, but the peak total gain figures are similar among the 3 for the two frequencies I used: 3.5 and 7.2 MHz. Here is a summary of results:

Maximum Total Gain (dB)

@ 3.5 MHz @7.2 MHz
110 ft dipole 5.53 6.59
Horizontal Loop of 287 ft 6.39 5.83
133 ft OCF Dipole 5.74 6.42

Radiation patterns for the 2 frequencies are shown in this PDF file. If you zoom in enough you can read the data on each graph.  Patterns for additional frequencies are easily generated.

I used a similar side-by-side presentation in this 2010 posting when comparing two antennas sized for 160 m (110 ft or 130 ft wire to each side of the feed point).


Friday, January 9, 2015

Feedline Loss & Other Characteristics

Here are some online resources you can use to calculate the loss and other characteristics for specified feedline types or geometries:

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