Homebrew Delta Loops
Delta-loop antennas are a great example of a high performance yet modest antenna. The single-element loop antenna is almost exclusively used on the low bands and can produce large amounts of low-angle radiation. It requires only a single quarter-wave high support. It will act as an array of two phased verticals, however the ground requirements are the same as for any other vertically polarized antenna.
Low delta loops mean the horizontal wire will couple to lossy ground and allow for some losses, unless the ground is improved by putting a ground screen under the antenna.
Many say that delta loops don’t require a decent ground system. however this is a bit like saying that a vertical antenna with a single raised radial does not need a solid ground system.
Loops antennas are particularly useful on 80 and 40 meters . A resonant loop antenna will have a circumference of 1 λ. The exact shape of the loop is not very important. In free space however, is the loop with the shape that encloses the largest area for a given circumference will have the most gain. This is a circular loop, which is not often easy or possible to construct. Second best is the square loop also known as a quad element. Next is the equilateral triangle or delta loop.
The maximum gain of a 1-λ loop over a λ/2 dipole in free space is approximately 1.35 dB. Delta loops are used extensively on the low bands at apex heights of λ/4 to 3λ/8 above ground. At such heights the vertically polarized loops far outperform dipoles or inverted-V dipoles for low-angle DXing, assuming good ground conductivity.
Whether or not the loop produces a vertically or a horizontally polarized signal (or a combination of both) depends only on how (or on which side) the loop is being fed.
Low delta loops mean the horizontal wire will couple to lossy ground and allow for some losses, unless the ground is improved by putting a ground screen under the antenna.
Many say that delta loops don’t require a decent ground system. however this is a bit like saying that a vertical antenna with a single raised radial does not need a solid ground system.
Loops antennas are particularly useful on 80 and 40 meters . A resonant loop antenna will have a circumference of 1 λ. The exact shape of the loop is not very important. In free space however, is the loop with the shape that encloses the largest area for a given circumference will have the most gain. This is a circular loop, which is not often easy or possible to construct. Second best is the square loop also known as a quad element. Next is the equilateral triangle or delta loop.
The maximum gain of a 1-λ loop over a λ/2 dipole in free space is approximately 1.35 dB. Delta loops are used extensively on the low bands at apex heights of λ/4 to 3λ/8 above ground. At such heights the vertically polarized loops far outperform dipoles or inverted-V dipoles for low-angle DXing, assuming good ground conductivity.
Whether or not the loop produces a vertically or a horizontally polarized signal (or a combination of both) depends only on how (or on which side) the loop is being fed.
The delta loop is ideal and very popular because of its shape with the apex on top it needs only one support. In free space the delta loop produces the highest gain and the highest radiation resistance for a three-sided loop configuration. If the shape is changed from an equilateral triangle to a triangle with a long baseline, the gain and the radiation resistance of the loop will decrease it is therefore best to keep each side as equal in length as possible.
You can change from horizontal to vertical polarization by changing the position of the feed point on the loop. For horizontal polarization the loop is fed either at the center of the baseline or at the top of the loop. For vertical polarization the loop should be fed on one of the sloping sides, at λ/4 from the apex of the delta.
You can change from horizontal to vertical polarization by changing the position of the feed point on the loop. For horizontal polarization the loop is fed either at the center of the baseline or at the top of the loop. For vertical polarization the loop should be fed on one of the sloping sides, at λ/4 from the apex of the delta.
In vertical polarization the delta loop is like two sloping quarter-wave verticals (their apexes touch at the top of the support), while the baseline feeds the “other” sloper with the correct phase. The top connection of the sloping verticals can be left open without changing anything about the operation of the antenna. The vertically polarized delta loop is an array of two λ/4 verticals. The fact that the tops of the verticals are close together does not influence the performance to a large degree. The reason is that the current near the apex of the delta is at a minimum (it is current that takes care of radiation!).
With a pair of phased verticals the quality of the ground will have a bearing as to the efficient operation of the antenna:
This does not mean that the delta loop requires radials. It has two elevated radials that are already built into the loop and take care of the return currents. The presence of the (lossy) ground under the antenna is responsible for near-field losses, unless we can shield it from the antenna by using a ground screen or a radial system, which should not be connected to the antenna.
As with all vertically polarized antennas the quality of the ground within a radius of several wavelengths will determine the low-angle radiation of the loop antenna.
With a pair of phased verticals the quality of the ground will have a bearing as to the efficient operation of the antenna:
This does not mean that the delta loop requires radials. It has two elevated radials that are already built into the loop and take care of the return currents. The presence of the (lossy) ground under the antenna is responsible for near-field losses, unless we can shield it from the antenna by using a ground screen or a radial system, which should not be connected to the antenna.
As with all vertically polarized antennas the quality of the ground within a radius of several wavelengths will determine the low-angle radiation of the loop antenna.
In horizontal polarization operation, delta loops can be seen as an inverted-V dipole on top of a very low dipole with its ends bending upwards to connect to the tips of the inverted V. The loop will perform like any horizontally polarized antenna over real ground; its wave angle will depend on the height of the antenna over the ground.
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Inverted V Dipoles
80m Inverted V Dipole, click to enlarge
The inverted V dipole is a modest yet great antenna! Often called the poor mans dipole as it only requires one support structure, this coupled with the fact that it takes up less space on your property than a flat top. The radiation resistance an inverted V changes depending on its height above the ground. The inverted V is no doubt a compromise antenna when compared to the flat top dipole. At low heights this gain difference is minimal, but at heights that produce low-angle radiation the flat top does perform substantially better. On many occasions it will be more feasible to erect an inverted-V dipole antenna much higher than a flat top dipole, mainly because there is only one high support structure available. Taking this into account a high inverted V can be superior to a low horizontal dipole. The inverted V loses out compared to a flat top dipole at the same apex height, but having said that not all amateurs have two equally high supports. The length of an inverted V depends on both the apex angle of the antenna and the height of the antenna above ground. Reducing the apex angle ie closing the legs of the inverted-V will increase the resonant frequency. However the antenna will become electrically longer when closer to the ground due to the end-loading effect of the ground on the inverted-V ends.
Sloping Dipoles aka Slopers!
A very simple yet highly effective dx antenna for the low bands.The half-wave sloper generates a signal with both horizontal and vertical polarization parts. Low-angle radiation will be produced only by the vertical component. The weight of the feed line means that any sloping dipole will rarely have two halves in a straight line.The steeper the slope, the less horizontal radiation component there will be. High-angle radiation is only due to the horizontal radiation component.
Most installed sloping half-wave dipoles have a bent wire shape, because of the weight of the feed line attaching at the feed point. The sloping dipole with a relatively horizontal bottom quarter-wave wire will yield about the same signal as the straight sloping dipole. It is however necessary to keep the top half of the sloping dipole as vertical as possible. The angle of the bottom half of the antenna is not so important,
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