When it comes to antennas, the phrase “height is might” is often used. Let’s take a closer look at the physics and do some math to understand this in practical terms.

Antenna height at HF

HF antennas tend to be mounted relatively close to the earth in terms of electrical wavelengths. This means that the ground interacts with the antenna in a variety of ways.

The two main factors that come into play for HF antennas are:

  • Angle of radiation:   For long distance HF communications, the lower the angle of radiation the better. But if an antenna is too low to the ground it will force the angle of radiation skyward. The rule of thumb is that antennas should be at least half a wavelength high. To operate in the 20 meter band or above you would want your antenna at least 10 meters (about 33 feet) above ground. This can be relatively easy for most of us, but for lower frequencies with longer wavelengths more height is needed, and this can be a challenge. See my article on NVIS.

    It is possible to calculate the elevation of the lowest lobe for a horizontal antenna above a perfectly conducting ground. It can be determined from this formula: θ=(sin(−1))(0.25/h) Where:
        θ = the wave or elevation angle for the lobe
        h = antenna height above ground in wavelengths

    Of course, the ground is not a perfectly conducting surface, and this too will affect radiation, but we shall save this for a future discussion.
  • Radiation losses:   When an antenna gets closer to the ground, then the losses due to the ground itself become more important and, at very low heights above ground, this will be the main factor determining antenna performance. For example, for a signal at 3.5 MHz, the wavelength is around 80 meters. A new radio amateur buys the nicest dipole antenna he can afford and strings it from the peak of his roof to a tree on the other side of the yard. It is perhaps 20 feet above ground. At these heights relative to wavelength, ground losses will be the dominant performance factor, easily reducing the antenna to 50% efficiency or below – meaning that before the signal leaves the yard half the power will be lost as radiation losses.

Antenna height for VHF & UHF

At VHF and UHF, radio propagation tends to be more line of sight, although not always.

One of the main advantages of increasing the height of an antenna is that it raises the antenna above other items that might obstruct the antenna’s line of sight. Trees, houses and the like will all absorb radio signals, especially at VHF and UHF frequencies.

Raising the antenna above nearby objects like houses and trees will also tend to separate the antenna from nearby sources of undesirable radiation.

A further advantage at VHF and UHF is that the higher the antenna, the more distant the radio horizon. The radio horizon is often taken to be 4/3 the visible horizon as a result of the bending effect caused by refractive index changes close to the ground. Raising the antenna will considerably increase your horizon, and thereby extend the range of your transmissions.

The height gain, however, needs to be balanced against feed line loss. At VHF, and even more so at UHF, the losses in the feed line become considerable, and in some instances may exceed the gain resulting from increased height. Obviously, using the best feed line possible will make a difference. If you plan to get your antenna up high, then also plan on investing in high quality low loss feed line.

Antenna height and interference

By their very nature, antennas that are higher tend to be removed from other electronic and electrical items by a greater distance.

This has two effects. One is that as a receiver connected to the antenna is further away from any sources of interference on or near the ground. The second is that the transmitted signal from the antenna will be further away from anywhere that interference from the transmitted signal may cause an issue.

Antenna height and RF exposure

There is a growing awareness of exposure to RF. Where transmitters may carry relatively high levels of radiated RF power, this needs to be kept as far away as possible from any areas frequented by people or pets.


When planning the height of an antenna, many factors need to be considered and balanced. Greater height provides greater operational range, but at the cost of visual impact, additional cost for a mast, feed line loss, and other factors.

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