|Antenna 014: The G5RV
Author: Frederick R. Vobbe, W8HDU
November 28, 2008
The G5RV is an excellent all HF band antenna. It works well on 3.5 to 30 MHz. It's a dipole, using #14 to #10 wire, fed with laddar line. Because it's a dipole there are some directional qualities to it.
Specifically the G5RV is a 102 foot dipole with a 31 foot feeder of 450 ohm transmission line. You will need 110 feet between two points to attach the ends. And the mid point also needs to be supported. The height above ground should be at least 35 feet or higher.
It's design allows the transmission line to radiate so it achieves resonance on all bands from 80 to 10 meters. The impedance at the end of the 450 ohm feed line is 50-60 ohms. So you can attach the 450 ohm line to an SO-239 connector. Alternately, you can feed the end of the transmission line from a tuner. Figure 1 shows how the antenna looks.
Let's look at how this antenna functions. If you wish to optomised the G5RV you can calculate the "flat top" (dipole) length, we use the formula: 1428 / F Mhz = Length in feet. And the formula of the matching is: 468 / F Mhz X velocity of the twin lead = Length in feet. But for the sake of discussion lets assume our 102 foot dipole.
The image to the left is the vertical pattern. You're standing to the side of the antenna looking at where the bulk of the RF is going. The green line is the direction of the RF. In the 160 meter example, the RF is going straight up in the air. In the 30 meter example you see that the RF is taking off at a 40 degree angle, and when we get to 10 meters the signal lowers to an angle of just 13 degrees up, off the horizon.
The image to the right is the horizonal. You're flying over the antenna, looking down on the antenna. The antenna is stretching from left to right.
As you can see, the antenna's radiation pattern varies from band to band. One should consider this when building this antenna.
Frederick R. Vobbe, W8HDU
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