![]() This Blog is mainly dedicated to Amateur Radio (Ham radio) and contains external articles and personal esperiences.In the figure, a converging lens $\left(f_$ of the image produced by the second lens. IT System Engineer, recently started having fun with morse code and Raspberry Pi Licensed Amateur Radio operator in 1996 as IW5EDI, active member of ARI Firenze and ARRLĬlass 1970, married with two childrens, love experimenting and antenna home-brewing. Do not go below 18 feet though, because your antenna will start losing its radiation pattern (it will turn into an inefficient antenna).Īrticle by Scott originally available at Related Posts via Taxonomies Now if you wanted a high angle of radiation for strong contacts to close DX stations (500-1000) miles, you can set your antenna about 20 – 36 feet about the ground. Conversely, if you live in a valley where the surrounding landscape is elevated around your antenna, you must go as high as possible (I know that is obvious, but you can’t think if your antenna is 70 foot up in the air you are getting a low angle of radiation – your antenna “knows” its low compared to the surrounding landscape). If you live on a mountain top, or your home is elevated above the surrounding landscape, you can use the lowest minimum height (36 – 40 feet) because the lower ground around the antenna fools the antenna into thinking its higher and makes a low angle of radiation. Its best to get it up around 60 – 70 feet. What is “high” and what is “low” for 27MHz? Generally for a low angle, you want to get your antenna over 1 Wavelength from the ground (36 feet). Quads have a lower angle of radiation than Yagi’s when mounted at the same height also. Verticals are great DX antennas for this reason (to make your vertical antenna an even better DX antenna read the “Earth Ground” section). Actually, vertical antennas have lower angles of radiation than beams when mounted at the same height above ground. Do these antennas have the same angle of radiation? No, they do not. But, lets say we have a 4 element beam at 40 feet and a 1/2 vertical at 40 feet also. When we say that antenna height determines angle of radiation, this is a generalization. Note: The angles of incidence and reflection are always measured from the normal. Technically, at this high of an angle you signal would be attenuated too much to talk after about 4 hops, so your signal would never make it as far as this figure shows! The angle between the reflected ray and the normal is known as the angle of reflection (r). In Specular reflection, the reflected light field is preserved in certain ways which allow them to be focused to an image, although left-rght inverted. You can see, the first hop is much shorter resulting in stronger signals to closer stations (500-1000 miles). Answer (1 of 4): Diffuse reflection of light is the opposite of Specular (mirror) reflection. Figure 2 shows how a low angle of radiation takes a lot less hops to make it to a DX station as opposed to a high angle of radiation (figure 3).įigure 3 – The high angle travel less distance each hop. So, if you are trying to talk to very very distant stations (other side of the earth), low angle of radiation is very very important. For every hop a your signal it has to take, the more its strength is reduced. ![]() Secondly, a lower angle of radiation strikes the ionosphere (the part of the atmosphere that your signal bounces off when you are talking “skip” (DX)) at a lower angle, and thus is able to “skip” to a DX station with less hops. If you concentrate your signal at a lower angle, it travels farther on the ground before it finally bends (the earth actually curves away from the signal) away from the earth. One, low angle of radiation is great for long distant groundwave talking. Lower angles of radiation are better for two things. Why is this angle of radiation important? Simple. Quite simply, the higher then antenna is, the lower the angle of radiation. To get this angle of radiation you will need to have your antenna from about 70 ft – 25 ft, respectively. The shaded area shows the most useful angles (10 – 20 degrees). This figure shows a vertical antenna, but the concept is the same for all types of antennas.
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