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H.F Dish Antenna update
In the past I mentioned that I was modelling an antenna for 20 metres.
This antenna became a single driven element with five reflectors which emulate a dish in it's crudish form not only in position of reflectors but also the elements were not shaped at this time. The following table follows what one would get for a reflective dish used on frequencies in the giga hertz range where the bandwidth is broader than that obtained with the yagi format PLUS relevant atributes stay more constant over a frequency range than that obtained with a super gain type array. The band width is wider than a typical yagi in that the major portion of the radiation is to the front this.This band with is expected to narrow and to increase gain when individual elements are shaped to a parabolic form and it is hoped that forward side lobes will not occur as is normal for a long boom multi element yagi form as used on 440 Mhz. The driven element is at a height of 76 feet over perfect ground. Normally one would say that if results seem out of the ordinary one should question it, so comments are requested regarding my explanations which lead me to think that they really are what one should expect. Freq 14.0 14.1 14.2 14.3 14.35 Gain dbi 13.86 14.05 13.99 13.9 13.87 F/B 30 25.6 27.47 33.17 32.5 Zr 45.9 44.5 43.8 43.2 42.8 Zi -12.87 -6.52 0.6 7.84 11.54 SWR 1.32 1.2 1.14 1.25 1.34 I do not advocate the replacement of the normal yagi with the above because of building difficulties tho it is my intention to build it. Regards Art (Modelled using AO PRO with 80 segment/half wave and set up by a consumate error generator Grin ) |
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