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Marconi,
Those examples do show that the angle of 'droop' of the radials of a typical groundplane antenna determine it's input impedance. Of those examples, the second one is probably the most commonly thought of what a 'groundplane' antenna looks like. It had an input impedance of around 23 - 25 ohms, right? As that 'droop' got larger the input impedance went up until it was 'close' to what a vertical dipole's input impedance is.
You have to realize that 35 ohm thingy is a generalization, sort of the average guess, it's not exact at all. If you average the high and low examples, what does the -average- or typical input impedance come out as?
I think you just 'proved' that 35 ohm -generalization-.
Another aspect of modeling programs is that they are ALWAYS a generalization, never exact unless you provide a huge amount of input data to show the antenna's environment and how the thing is constructed. Until you can provide that level of input data the results are never going to be 'exact' by any means. (Don't know about you, but I have no way of accurately finding all that data.) So, while the modeling programs are certainly useful, I don't think I'd bet the farm on them.
- 'Doc

<blockquote data-quote="W5LZ" data-source="post: 441087" data-attributes="member: 129">Marconi,Those examples do show that the angle of &#039;droop&#039; of the radials of a typical groundplane antenna determine it&#039;s input impedance.&nbsp; Of those examples, the second one is probably the most commonly thought of what a &#039;groundplane&#039; antenna looks like.&nbsp; It had an input impedance of around 23 - 25 ohms, right?&nbsp; As that &#039;droop&#039; got larger the input impedance went up until it was &#039;close&#039; to what a vertical dipole&#039;s input impedance is.You have to realize that 35 ohm thingy is a generalization, sort of the average guess, it&#039;s not exact at all.&nbsp; If you average the high and low examples, what does the -average- or typical input impedance come out as?I think you just &#039;proved&#039; that 35 ohm -generalization-.Another aspect of modeling programs is that they are ALWAYS a generalization, never exact unless you provide a huge amount of input data to show the antenna&#039;s environment and how the thing is constructed.&nbsp; Until you can provide that level of input data the results are never going to be &#039;exact&#039; by any means.&nbsp; (Don&#039;t know about you, but I have no way of accurately finding all that data.)&nbsp; So, while the modeling programs are certainly useful, I don&#039;t think I&#039;d bet the farm on them.&nbsp;- &#039;Doc</blockquote>

[QUOTE="W5LZ, post: 441087, member: 129"] Marconi, Those examples do show that the angle of 'droop' of the radials of a typical groundplane antenna determine it's input impedance. Of those examples, the second one is probably the most commonly thought of what a 'groundplane' antenna looks like. It had an input impedance of around 23 - 25 ohms, right? As that 'droop' got larger the input impedance went up until it was 'close' to what a vertical dipole's input impedance is. You have to realize that 35 ohm thingy is a generalization, sort of the average guess, it's not exact at all. If you average the high and low examples, what does the -average- or typical input impedance come out as? I think you just 'proved' that 35 ohm -generalization-. Another aspect of modeling programs is that they are ALWAYS a generalization, never exact unless you provide a huge amount of input data to show the antenna's environment and how the thing is constructed. Until you can provide that level of input data the results are never going to be 'exact' by any means. (Don't know about you, but I have no way of accurately finding all that data.) So, while the modeling programs are certainly useful, I don't think I'd bet the farm on them. - 'Doc [/QUOTE]

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