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#8
November 6th 09, 03:52 AM
posted to alt.internet.wireless,rec.radio.amateur.antenna
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Matching impedance with coax
who where wrote:
On Wed, 04 Nov 2009 20:10:53 -0600, tom wrote: who where wrote: I suspect that the design of the MFJ antenna was done in a way which places the parasitic elements close enough to reduce the folded dipole's impedance to somewhere in the neighborhood of 50 ohms. All that would be necessary, then, to allow a direct feed from a 50-ohm coax, would be a choke balun (to convert the unbalanced coax feed to a balanced drive to the folded dipole, without altering the impedance). The presense and spacing of the parasitic elements isn't going to change the feedpoint impedance that much. Wrong. It can change it a lot. It can take a 50 ohm DE and move it to 10 ohms or less. And then there's the reactive part. Well you can believe what you like. I believe what occurs and is measurable. tom K0TAR |
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