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Field Day 2018 Phone Station Antenna Map and Patterns

By

John Raydo, K0IZ

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Our 2018 Field Day Phone Station antenna. It is a two-leg V-Beam. The center (on a mast) is sited near the operating tent (white square). One leg then goes to NE, tied to a tree. The other leg goes SE, attached to our second mast. Each leg of the V-beam is 180 feet long.

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During Field Day we noticed that North Carolina stations were worked in abundance. We guessed that the antenna had a large lobe of signal pointed in that direction. After Field Day I used EZNEC antenna simulation program to see what was happening.

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This is an azimuth plot, at 25 degrees’ elevation, of a typical 20 Meter field day dipole. In this simulation the dipole runs north-south, with best signal to the east and west.

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Same 20 meter dipole, this is an elevation plot. Note that highest gain is at about 23 degrees. Also note the substantial upward signal, which is totally wasted (unless talking to someone else in Shawnee!). The upward signal is only about 4 db lower than the maximum signal and is wasted signal. The dipole is at 43 feet height.

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This is a plot of a dandy 5-element 20 meter beam, pointed to the east. Nice clean pattern with minimum side and rear lobes. Plot is also at 25 degrees’ elevation and 43 feet height.

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And here is a plot, at 25-degree elevation, of our 2018 field day V-beam antenna. Note the big gain in the direction of North Carolina. The simulation confirms our field day experience. I used 25 degrees’ elevation for the plots since this would be a typical take-off angle to work stations towards both coasts and in-between. For DX, however, we would be more concerned with gain at 5 to 10-degree elevations.

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Now a comparison of our typical 20-meter dipole and our 2018 V-beam. Note that in almost every direction the V-beam is better than the dipole. In several directions there is 8 to 10 db improvement. 10 db makes our 100 watts sound like 1KW. No wonder every ham in North Caroline called us!

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During field day I speculated that perhaps opening up the angle between legs (about 58 degrees) would spread out the propagation. The black is our 2018 antenna. The red is a proposed change for 2019. The new angle is about 82 degrees.

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And here’s the plot of the proposed 2019 V-beam antenna.

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This plot compares the 2019 antenna (in black) with the 2018 antenna (in red). Note that the “North Carolina” lobe has been reduced by about 3 db. But we have a very nice lobe at about 200 degrees that points right at Dallas. We should work lots of Texas stations since this lobe is about 10 db higher than the 2018 antenna.

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Our 2019 antenna has a low angle of radiation (about 18 degrees at the peak). And at 10 degrees the radiation is only about 2 or 3 db down from the peak. Great for DX. For Field Day, however, 25 degrees is better and about 2 db down from the peak. Still good. Note that the wasted energy going up is about 10 db less than the dipole.

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Here we compare the 2019 antenna (in black) with our 20 meter dipole (red). Note that “North Carolina” is now only 8db better than the dipole. Still makes our 100 watts sound like 630 watts. And Texas is hugely better, some 13 db (2KW equivalent!). And good gain elsewhere with a couple of very minor exceptions.

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Here we compare our proposed 2019 antenna (black) to a 5-element beam (red) pointed east at a 25 degree elevation. Note that both antennas are more or less equal going to the east. If we don’t rotate the beam, the 2019 antenna is much better in all other directions. Signals on Field Day come from all directions, so a highly direction beam antenna is not ideal, as this plot shows.

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This is the V-beam antenna as simulated in EZNEC. About 154 feet of each leg is comprised of two wires, spaced one foot apart. This section is then followed by three coaxial traps. The antenna is resonant on 80, 40, 20, 15, 10, and 6 meters and does not need an antenna tuner.

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This is an excerpt from my QST article back in 2005. The diagram shows the 154 foot section of double wire, followed by the three traps. The traps are parallel-resonant at 20, 40, and 15 meters and appear as open circuit at those frequencies. Thus for 20 meters, the antenna is effectively 154 feet long. For 40 it is 165.5 feet, and so forth.

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This is a 20M SWR plot of the proposed 2019 antenna. At the design frequency of 14.225 Mhz, the SWR is 1.2 to 1, and varies from 2.4 to 2.0 at band edges. The double wire makes that section of each leg appear to be made of “fat” wire, equivalent to approximately 3” in diameter (with the 1 ft spacing).

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This is the identical antenna with only a single wire in the 154 ft section. The “skinny” 14 ga wire has a higher SWR of 1.6 at 14.225 and much higher at band edges. Similar results can be demonstrated for other bands. The idea of “fat” wires can be utilized with virtually any wire antenna. For example, a G5RV can be constructed with ladder line rather than wire. The ladder line (ie two wires spaced about ¾”) makes a good antenna better.