MY YAGI LFA ANTENNAS FOR 144 MHz

    Here you can find data and parameters for building LFA (loop fed array) antennas. They differ from other yagi antennas for their radiator which is made in form of loop, placed in the same plane with parasitic elements. The loop can be a rectangle or a trapeze. I prefer the second one, because it offers a little bit better opportunities for modelling.

    The rectanle/trapeze can be fed in the wire facing reflector or facing first director.

    The term `LFA` was established by G0KSC. His LFA antennas are 50 Ohms at feed points, however, my models are almost all designed for 200 Ohms impedance.

    There is a big choice of yagi antennas. Therefore, I paid more attention to modelling Oblong, Tween boom and Hybrid antennas, because they are expected to give better results than Yagis and, also, becauce the choice among them is not so big. However, I have finally realized that the choice of LFA yagis with 200 Ohms feeding is not so big, either. That was the reason that I made a collection of these yagis

    The 200 Ohm design offers, more or less, the same gain characteristics as 50 Ohm yagis, but one can wish to build 200 Ohm antennas because they can be simetrized more efficiently, by using 1/2 WL baloon

    When building my LFA models, you will see that the dimensions and positions of reflector and first director regarding radiator are quite critical. Do not be afraid of this! The only thing changing is SWR! All other parameters will remain almost unchanged within wide error limits! Therefore, use this fact for fine SWR tuning.

    In the Table of my models, given bellow, I give the data for some antennas accepted in the VE7BQH Table, just for comparison.

    CONSTRUCTION

    All parasitic elements are made as usual for any yagi antenna. They are calculated with no influence of boom. Therefore, the elements have to be isolated from the boom, or a boom correction factor must be used.

The following picture gives a typical shape of radiator (in this specific case, the radiator belongs to the Y21105XL7B model):

    Note that the shorter end is always bordering with first director, and the longer one with reflector. In the dimension tables I give the shorter length and the longest length and the distance between them. Therefore, you have to calculate all other dimensions by yourselves!

    The feed points are at the 10 mm gap. Since the impedance is 200 Ohms, you have to use a balun made of 50-Ohm coax ½ WL long.

    This LFA yagi collection consists of new redesigned antennas in order to meet the VE7BQH requests (f₀=144.100 MHz), so that they can be compared against the other antennas in the VE7BQH list. All models data are calculated using KF2YN correction formula. NOTE: Corrected data for gain and G/T are given in the Tables only. The gain data in the EZNEC patterns and diagrams are not corrected! All other parameters, including F/B, F/S etc, do not change, so that they can be used from the EZNEC patterns and diagrams.

    Now you will see the table with all LFA models. Use it to choose a model or to compare characteristics. If you want to see details for a specific model, just click on the name of the model.

    Good luck in building and Dxing!