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Current through a coil in an antenna.
If we feed an antenna at the current point, the current decreases as the voltage increases along the antenna element from feed point to end.. That being said, a coil replacing a segment of an antenna (in order to physically shorten it) will exhibit the same properties (relating to currents) as the segment it replaced. "Richard Clark" wrote in message ... On 30 Oct 2003 22:59:26 GMT, oSaddam (Yuri Blanarovich) wrote: If we suppose the loading coil is heating up equally Hi Yuri, You have already testified twice that it does not - so why IF it around? 1.) If you trasmit for short period of time (not enough for heat to equalize) and feel it, or use thermal strips to check temperature, you would see the taper in the current from bottom to top. It is in order of 50%, not negligible. 2.) Put 500W to it for longer period and watch the heatshrink tubing shrivel from the bottom up. 73's Richard Clark, KB7QHC |
#3
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w4jle wrote:
Current through a coil in an antenna. If we feed an antenna at the current point, the current decreases as the voltage increases along the antenna element from feed point to end.. That being said, a coil replacing a segment of an antenna (in order to physically shorten it) will exhibit the same properties (relating to currents) as the segment it replaced. Yep, if the feedpoint impedances are the same and both are lossless, that has to be true. Here's a repeat of a diagram I drew earlier. -----y----------x-----FP-----x----------y----- 1/2WL dipole -----coil-----FP-----coil----- loaded dipole Assume the physical length of the loaded dipole is 1/4WL. Each coil replaces the section between 'x' and 'y'. The currents at 'x' and 'y' are quite different, being 1/8WL apart. Consider an 8 foot center-loaded 75m mobile antenna. 87% of the electrical length of the antenna is in the coil. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
#4
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If reactance can be seen as a "{missing" part
of a radiator how should we view what a capacitor represents? Grin Art Cecil Moore wrote in message ... w4jle wrote: Current through a coil in an antenna. If we feed an antenna at the current point, the current decreases as the voltage increases along the antenna element from feed point to end.. That being said, a coil replacing a segment of an antenna (in order to physically shorten it) will exhibit the same properties (relating to currents) as the segment it replaced. Yep, if the feedpoint impedances are the same and both are lossless, that has to be true. Here's a repeat of a diagram I drew earlier. -----y----------x-----FP-----x----------y----- 1/2WL dipole -----coil-----FP-----coil----- loaded dipole Assume the physical length of the loaded dipole is 1/4WL. Each coil replaces the section between 'x' and 'y'. The currents at 'x' and 'y' are quite different, being 1/8WL apart. Consider an 8 foot center-loaded 75m mobile antenna. 87% of the electrical length of the antenna is in the coil. |
#5
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Art Unwin KB9MZ wrote:
If reactance can be seen as a "{missing" part of a radiator how should we view what a capacitor represents? Grin A series cap has the opposite effect of a series coil. I have seen such antennas made out of end to end caps but I've never really understood their claim to fame. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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