5.8 GHz fpv helix antenna 11 turn 14.4 dBi RHCP

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5.8 GHz fpv helix antenna 11 turn 14.4 dBi RHCP A diy antenna project for long range fpv. This is an RX side antenna (to mount on googles or tracker) This project has an RHCP polarization. The antenna is 13 cm long (excluding the cable and connector), the diameter is 24 mm (the base is 42 mm) and the weight is about 30 grams (including cable and connector) I made this antenna to extend the range of my 5.8 GHz fpv aircraft. In theory its gain is 14.4 dBi. The project is easy to implement. You need to create the 1mm copper wire helix first. To do this the template for the helix is ​​used. I suggest to "tighten" the coils by hand a little after having removed them from the template as they tend to widen a little. Then the helix must be mounted on the holder, "screwing" it into the holes. It may be necessary to grind the holes with a 1.2mm drill bit. In this way the operation is easier. Once this is done it is necessary to prepare the reflector. I used a 0.8 mm thick single-sided pcb, but I think 1.6 mm is also fine. You need to create a 42mm diameter disc with a 3mm central hole. Thanks to the hole it is possible to center the drilling template, included in the project. Start making 1mm holes, then enlarge the hole for the coaxial cable according to its size. I used a 3.4mm hard cable. The copper-plated part of the PCB goes outwards, the mass of the coaxial cable must be soldered on it. The central lead should protrude 0.4mm from the non-coppered face. To block the central support I welded three 5mm long wires which I then inserted into the holes in the support and bent to hold everything together. At this point it is necessary to create the tuning chip whose size depends on the characteristics of the PCB. In my case I cut a plate of tinned copper about 1 cm in the shape of a triangle with a rounded side. The pointed end is soldered near the joint between the helix and the coaxial cable. The function of this plate is really important as helical antennas do not have a standard impedance of 50 ohms and therefore must be tuned. This design was built with a no-load impedance of approximately 100 ohms. Helical antennas usually have an impedance of 140 ohms. I preferred to keep it lower in order to use a lighter tuning. This should benefit the real gain of the antenna. However, only one end of the plate needs to be welded (see picture) in order to facilitate tuning, bending it up or down to find the best performance. To tune the antenna for maximum performance, you need a vector network analyzer to connect it to and, by moving the plate, find the lowest SWR. If you don't have such a tool, then you have to weld the plate in a position almost parallel to the pcb and rely on luck. Unfortunately microwaves are really critical and sometimes a few tenths of a millimeter or a drop of tin somewhere can make the difference. In any case, once the support with the helix has been fixed to the reflector and the end of the helix has been welded to the coaxial cable and to the plate, after having done the tuning if possible, the first cover of the base can be inserted. I fixed it with a few drops of superglue to the protruding edge of the pcb. Then we move on to the protective tube, also fixed with a few drops of super glue, both at the base and on the top, where the helix support fits with the inserts. The job is done. P.S. tuning FPV antennas is always a quite critical stuff. In principle and from my personal experience, I have noticed that a bare antenna always resonates at higher frequencies than when it is covered with a protection. For example, this project was born with a reference frequency of 5900 MHz. Once the bare antenna has been tuned, the frequency more or less remains unchanged, but as soon as the molded protection is mounted, we notice a frequency shift downwards to 5800 MHz which is the goal of the project. It is possible to play with the material and thickness of the shells to further refine the tuning. Using standard PLA, this antenna, with pods fitted, tunes to approximately @5800 MHz. This antenna was designed with the tool found at this link: https://sgcderek.github.io/tools/helix-calc.html and the following parameters were used: F user input 5900 MHz Operating frequency Sλ user input 0,23 λ Spacing between turns n user input 11 Number of turns Cλ user input 0,715 λ Helix circumference (normally 1) Have a good flights!