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Tonna 9 element 70cm yagi - feed method?
In UK we have 430MHz to 440MHz. I checked the 'SWR' by measuring return
loss at 1MHz steps from 420MHz to 450MHz.. The radiation pattern was measured outdoors above a snow covered field (the nearest thing I have to laboratory conditions!) at 435MHz and polar plot made automatically. I also ran the test with two ferrite blocks on the cable next to the antenna connector. These were of unknown type but supposed to be similar to type 67. The blocks eliminated the skew with no measurable change in return loss. The initial skew was really quite small compared with the 3dB beamwidth but was recognisable on the plot, particularly on the sharper rear lobes. Curiously there is no skew shown on the plot in the manufacturers datasheet 220909e.pdf but their photo does show a black 'lump' just to the rear of the connector. Perhaps they did have a ferrite on there after all! Dick G4BBH "Channel Jumper" wrote in message ... Richard Ferryman;800950 Wrote: I have come by a Tonna 9 element yagi for 430MHz to 440MHz. The driven element is a folded dipole and has an n-type connector attached. SWR looks correct and it works but there is a slight skew to the radiation pattern. The n-type connector is potted in a plastic or epoxy and looks too small to have any sort of balanced to unbalanced device in it. I intend putting a ferrite choke on the feed cable to help. Tonna antennas have a good reputation and I am surprised at the apparent feed method. Does anyone know if I have missed something? Dick G4BBH First you cannot check antenna resonance with a SWR meter, that only tells the story of the feed line. You need a dip meter or a antenna analyzer. Second - you can use a loop, or a 1:1 Balun inline or beads.. My question is - what frequency do you want it for and what do you want to do with it =- transmit or receive? 430 - 440 is not within the parameters of amateur radio for repeaters.... You could talk simplex or work slow scan television and CW / Digital modes and that is about it. -- Channel Jumper |
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