The 6-Wire Flat Top

by MD0MDI
6-Wire Flat Top - Figure 1

6-Wire Flat Top Antenna

In last month’s issue we looked at the center fed multi-wire flat top antenna, which was a popular antenna back in the days of spark. This month we will examine the end fed 6-wire flat top, another popular antenna.. The antenna being examined has been scaled down from the dimensions given to me by an old timer that had used the antenna with his rotary spark transmitter back before WWI. The dimensions are more in line with what we have to deal with as far as small cramped dwelling lots and yards are concerned today.

Figure 1 shows the general configuration of the antenna without the supporting masts being shown. In this case the antenna is 60 ft.(18.24 meters) tall and 60 ft long (18.24 m).

6-Wire Flat Top - Figure 1
6-Wire Flat Top - Figure 1

The first band we will look at is 160 meters. Figure 2 is the polar plot of the antenna and it is almost a circle, indicating a slight bit of directivity at 180 degrees. 

6-Wire Flat Top - Figure 2
6-Wire Flat Top - Figure 2

Figure 3 is the vertical plot and it also shows a slight directivity to the rear with a very small bit of gain at 133 degree elevation.

6-Wire Flat Top - Figure 3
6-Wire Flat Top - Figure 3

If you have been reading antenneX for any length of time, you have seen the 3D plots that have been pictured previously. In this case, the 3D is not here as it resembled a dinner roll, but by using a little imagination, you can visualize what it would look like.

Nest we will see the patterns produced on 75 meters. Figure 4 is the polar plot of the antenna on 3.6 MHz. In this plot, a definite oval can be seen with some directivity to the sides of the array. 

6-Wire Flat Top - Figure 4
6-Wire Flat Top - Figure 4

Figure 5 shows a definite gain straight up of 4.15 dB. This would be a good antenna for local coverage out to 600-900 miles, with good signal strengths at right angles to the antenna. There would be some loss off of the ends of the antenna, but not enough to really worry about.

6-Wire Flat Top - Figure 5
6-Wire Flat Top - Figure 5

Moving to 40 meters the, vertical plot in Figure 6 shows a maximum vertical lobe at 51 degrees, with 1.41 dB gain. There is a deep notch slightly off vertical which should null out strong locals. The horizontal plot indicates a very slight directivity, with a front to back ratio of 8.12 dB. The horizontal plot indicates the minor directivity of the antenna on 40 meters

6-Wire Flat Top - Figure 6
6-Wire Flat Top - Figure 6
6-Wire Flat Top - Figure 7
6-Wire Flat Top - Figure 7

On 30 MHz, the antenna plot in Figure 8 again shows slight directivity towards the front of the array, at 0 degrees. 

6-Wire Flat Top - Figure 8
6-Wire Flat Top - Figure 8

The vertical plot in Figure 9 reveals a major lobe at 36 degrees vertical elevation with a 2.21 dB gain. There is a minor lobe to the rear that is slightly lower in gain. This is an indication that the antenna would not be too bad for DX on 30 meters.

6-Wire Flat Top - Figure 9
6-Wire Flat Top - Figure 9

There is no 3D pattern here because as the frequency was increased, the 3D pattern began to resemble some sort of squash plant or jungle fungus. There will be some 3D patterns displayed later.

Originally posted on the AntennaX Online Magazine by Richard Morrow, K5CNF

Last Updated : 14th March 2024

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