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#11
October 20th 04, 01:21 AM
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"Chuck" wrote in message news:n5gdd.8202$6P5.3752@okepread02... wrote in message news:x_Ycd.281755$3l3.162866@attbi_s03... What brought this to my attention was Moxon who advocated 2 element beams (lightnes translates to greater heights) so I modeled a 20 meter beam on a 7 foot boom and obtained 12dbi max for the band (ala 2:1) Hi Art, Can we assume this gain was calculated at a particular height over ground? But ofcourse a perfect ground and a standard wavelength height Personally, I prefer FS results, in order to eliminate any ambiguity. Field strength (F.S.) introduces ambiguity does it not? but one can get 13dbi if you drop the impedance from 50 to 12 ohms. This paraphrases the spesific example that I gave the question would a transformer cancel the increased gain. Again you paraphased the spoecific sample that I gave which raised the same question I gave regarding transformer losses Optimizing an antenna for a specific Z is not a good idea in my opinion, as the amplitude of an element's current is proportional to the amplitude of its radiation. Ohms law tells us that at a consistant power level, the lower the R (Z), the greater will be the current. Yes there are many laws to remember and I look at critical coupling as something to remember. A zero loss transformer would not reduce the element's current, as the energy being introduced to the element would remain unchanged. Very true but what element would this max energy be applied to? Via critical coupling the driven element may not be the one carrying the maximum current and thus screws up conventional thinking. Energy is one thing but it is current that controls radiation is it not ?. The particular model I was working on used 50 segments per wavelength and used element length and diameters determined by my program input . Thus coupling gains are attained but where it sometimes determined a element diameter is so thin it is incapable of carrying the required current. If I saw a vendor advertise an antenna at 13dbi I would be very suspicious as it not the norm, yet very realiseable when using NEC without being tied down to existing doctrines. Sooooooo ..... I was looking for a datum curve generated by experts from an all encompasing NEC program where the final design reflected the real world design without ambiguities regarding coupling to coils, elements e.t.c. where lumped loads do not reflect the real world appearance. There have been many responses including one suggestion that a suitable datum curve could be formulated from customer claims no less but NONE that responds to my specific request . Thus a conundrum still exists regarding programs based on scientific knoweledge that are held in question as they do not match real world measurements that spawn most of the villifying in this group. Seems like a datum curve could be used as a basis for many discusions where differences do occur instead of just arguing for eight years or more and not resolving the accuracy concerns Seems like I have come full circle and describing the Presidential debates ! Art 73 de Chuck, WA7RAI |
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