Delta Loop antenna . Antenna that allows the reception of electromagnetic waves used mainly by radio listeners. The Amateur Radio use them to your contacts nationwide and even for long distance , just to have enough space there for its location, its size somewhat high compared to dipoles .
Summary
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- 1 Features
- 2 Construction
- 3 Placement
- 4 Adjustment
- 5 Reception
- 6 Gain
- 7 Sources
characteristics
It is in this aspect that the delta loop is exceptional as an antenna. The delta loop is the bionic ear of wire antennas . Due to its closed shape, it is much less prone to picking up static and noise from surrounding sources, and although it has a noticeable attenuation in reception compared to other antennas, it is this attenuation that often allows weaker signals to be removed from the background out of nowhere . A Delta Loop can be built for any band, limiting only the space we have available to place it. The shape of the loop can be significantly distorted or tilted without greatly affecting antenna performance, as mentioned by Doug DeMaw (W1FB) andRead Aurick (W1SE) in the article “The Full Wave Delta Loop at Low Height”, which makes it much more attractive than a dipole or a vertical antenna for large wavelengths . However, it is the ability to listen with less noise that makes the Delta Loop (or any loop in fact) a very noble antenna to work with these large wavelengths, which are often plagued by an intense level of noise.
Building
The Delta Loop is made from a continuous length of conductor , and is one wavelength long. As for the conductor that is used, it can be a common and current electric cable , however this type of cable becomes very heavy when it goes over 10 m in length, and the loop tends to require a lot of tension to maintain its triangular shape . An alternative that gives very good results is the cable used for winding of transformer , which is a conductive solid of aluminumextremely light and easy to work. This cable is very good at looping, and is so light that the antenna can be tensioned using a 20lb fishing line . Let’s see the construction of the loop antenna:
- Since the antenna is a full wave, the length of your cable is not. 12 (from A, B , C , D , A ) is according to the formula L = 300 / frequency (in mhz ), therefore for the 40 meter band. It will be: L = 300 / 7,080 = 42.37 meters with this measurement it must resonate 1: 1.
- Before starting to assemble the antenna we must adjust our power line so that we can have correct antenna readings ( ROE, IMPEDANCE , REACTANCE , ETC) and not from our poorly calculated cable. Using 50- ohm RG-58 coaxial we have that the length of the coaxial will be Lc = ((300/2) /7.080) x 0.625 = 13.77 meters where: 300 is the speed factor of light, but as the power line must be half wave we divide by two and later we divide the result between the frequency of use and the final result we multiply it by the speed factor of the coaxial cable that we will use giving us as a result 77 meters in case of requiring more of those 13.77 meters we would add another 13.77 meters for our line to reach our radio room so that they are multiples of half wave in the power line. Now as we feed at point A with 13.77 mts reaches us since the point A is at most to 1.5 meters in height from the roof.
- Under the assumption that we have a toweror mast 18 meters high and the land space is not greater than 12 meters, then we have the following:
- Distance from Bto C 08 meters , distance from C to D 17.08 from D to A 4.11 meters and from A to B 4.10 meters Total of the wires will be: 42.37 meters as total of the triangle .
- At point A, the RG-58 coax will be connected. The center of the coax must be isolated from the mesh to connect to each end of the triangle. In addition, it must be stiffened to prevent the wind from breaking this connection, on the other hand, moisture must penetrate the coaxial and existing connections.
- Some people at this point Aconnect a Balun , but if you do not place it it does not affect the performance of the antenna as much.
- At points B, C , D only the supports will be placed that will allow the triangle to be properly tensioned to avoid variations and deformations of the antenna.
- If you want to add a director element, it is enough that you put a horizontal support about 3 or 4 meters long at the top of the tower, so that you can hang another triangle there and serve as director (this should be 5% smaller than the previous)
- Remember that the higher your triangle is, the better your working conditions will be. It is all a matter of adjusting to the space you have
Placement
The 50 ohm line can be coupled to the loop directly. For DX work , the most suitable way to position the loop is as DeMaw describes in his article: with the tip of the triangle facing up, and feeding it in a corner. This gives the loop vertical polarization and a low irradiance angle . To place a loop on a tower, the right triangle configuration , which is a distortion of the first configuration, and is also fed into a corner , may be helpful .
Fig 1
Other configurations, which provide high irradiation angles and are useful for local or regional work, are the top-up / tip-feed, tip-up / center-feed, and tip-down / tip-feed settings (See Fig 1). These provide horizontal bias, which can be useful for removing electrical noise from reception.
Adjustment
Rectangular delta configuration, useful for tower or mast.
The impedance of the delta loop by nature is 100 ohms. The easiest way to use this type of antenna is with an antenna tuner, which can very easily trick the team into showing you the 50 ohms that the equipment requires. A 2: 1 balun could also be used , which should give similarly good results. For the finest, there are other ways of coupling without a tuner . The first of these is to play with the placement of the feeding point. By moving the point along the vertical (or inclined in the case of a non-rectangular delta) leg, impedances of 50 ohms can be achieved , especially when the bottom of the loop is more than half a wavelength above the ground. This method is of little use to those of us who do not have the ability to loop more than half a wave above the ground, as it becomes too difficult to lower the impedance to a usable point.
Another method that works well at low altitudes is to use a piece of RG59 (75 Ohms) cable as a coupler. This allows the impedance to be lowered to a point close to 50 ohm. The 59 Ohms cable length to use is given by the formula 162.36 / f (MHZ), and will result in a length in feet that must be converted to meters.
Reception
Balun 4: 1 air core from 50 ohms to 200 ohms ideal for full wave antennas.
In terms of reception, the delta loop is a truly exceptional antenna, capable of reducing unbearable levels of noise to manageable levels, from which signals can be rescued. In low bands, a low altitude delta loop can be much more efficient than a dipole or an inverted V at the same altitude. In transmission a simple delta provides a certain gain (nothing spectacular) perpendicular to the plane of the antenna. The loop in its working band provides a low enough angle of irradiation that decreases the local intensity of the signals transmitted and received in various S units, (which is good because more signal is going out to the rest of the world), that is, the delta loop is not good for short distance chatting, but it works better than the dipole for long distance, due to its lower angle of irradiation.
Gain
Before vertical polarization delta loop with 4 to 1 balun.
If you plan to make an arrangement with 2 triangles (one as a reflectorand another as excited) you can significantly increase the gain of your antenna in a certain direction, you have two options: a) Make the reflector 4% longer than the excited element with a separation between elements of 0.10 full wave, you will achieve a impedance of 50 ohms. b) Or you build reflector 6.8% longer than the excited one at the same 0.10 wave separation, it will generate an impedance close to 100 ohms, without significantly changing your gain of the front-back of the antenna but the SWR will go to 2: 1, which will be corrected with a 2: 1 balun and thus you transform the SWR 1: 1 correctly. There are different types of arrangements according to the type of polarization presented by delta loop antennas. When measuring your delta at the feeding point with an antenna analyzer you have 200 ohms, you must put a 4: 1 balun to transform the impedances and from there you go down to the radius with 50 ohms impedance coaxial completing multiples of half a wavelength by its coaxial speed factor.