In a previous post we promised to analyze the merits of the 43 foot tall tuner-required antenna vs. the adjustable BigIR vertical from SteppIR. We did and here are the results.
First I should point out the SteppIR is about 33 feet tall so has the ability to adjust its height to 1/4 wavelength or 3/4 wavelength on the 10 and 15 meter bands. It can do this for 6 too. So for these bands we will compare, essentially, three antennas of which two are the BigIR.
All three antennas are shown below with the relative currents displayed.
All three antennas at 10 meters
Since 28 MHz is so short, the current profile along 43 feet of vertical radiator is long. The SteppIR BigIR in 3/4 wavelength mode shows a full half wave of current high up along with the 1/4 wave at the bottom. This is, of course, the definition of 3/4 wave. Finally the simple 1/4 wave vertical mode is on the right.
Here are the three patterns superimposed…
Elevation Gain Plots of 43' and SteppIR BigIR
The following characteristics are revealed:
The 43 foot vertical has its peak lobe at 56 degrees with gain of 5.6 dBi
The 3/4 wavelength mode of the BigIR has its peak lobe at 47 degrees with a gain of 3.9 dBi
The 1/4 wavelength mode of the BigIR has its peak lobe at 27 degrees with a gain of 0 dBi
Suprisingly, the SWR calculated from 28 to 29 MHz was well under 2 and often under 1.5 for each antenna
This comparison reveals each can work at 10 meters, but one has to argue the 43 foot antenna’s angle of radiation is a bit too high for practical use.
The 3/4 wave mode of the BigIR edges out the 1/4 wave mode just slightly at the low angles we desire for long haul DX. Still, who knows, you might gain some benefit from the 3/4 mode if your soil conditions and location are different and the BigIR lets you choose either. Another way to look at the 3/4 mode is a large half-wave radiator is somewhat elevated which may help clear obstacles close by; That could be a serious benefit over 1/4 wave. Pretty nice.
Next time we will analyze the 12 meters band the same way as above and keep going until we hit 160… or maybe just 80.
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