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Assuming there are no common mode currents present, a tuned electrical half wavelength feed line will faithfully recreate the conditions for X and R at the load (antenna). Any other point along the feed line will have differing values for X and R. If you are limited to SWR, any point along the feed line will show the same SWR, so if you have such a limit, an electrical half wavelength tuned feedline will do you no good.

Taking this a step further, many people think that simply because the X and R variables change that SWR will also change, when in fact, the relationship between X and R variables and SWR is such that on a half electrical wavelength of feed line every possible value combination of X and R for a given SWR will be present, and thus SWR is maintained, no matter where on the feed line the measurement is taken.

Further, if you know the electrical length of the feed line at the given frequency, it is possible to calculate what X and R are at the load itself.

All of this is not taking attenuation into account which on a half electrical wavelength of feedline will generally be very small, if it is noticeable at all.

The DB

<blockquote data-quote="The DB" data-source="post: 537714" data-attributes="member: 21346">Assuming there are no common mode currents present, a tuned electrical half wavelength feed line will faithfully recreate the conditions for X and R at the load (antenna).&nbsp; Any other point along the feed line will have differing values for X and R.&nbsp; If you are limited to SWR, any point along the feed line will show the same SWR, so if you have such a limit, an electrical half wavelength tuned feedline will do you no good.Taking this a step further, many people think that simply because the X and R variables change that SWR will also change, when in fact, the relationship between X and R variables and SWR is such that on a half electrical wavelength of feed line every possible value combination of X and R for a given SWR will be present, and thus SWR is maintained, no matter where on the feed line the measurement is taken.Further, if you know the electrical length of the feed line at the given frequency, it is possible to calculate what X and R are at the load itself.All of this is not taking attenuation into account which on a half electrical wavelength of feedline will generally be very small, if it is noticeable at all.<a href="http://hittman.us" target="_blank">The DB</a></blockquote>

[QUOTE="The DB, post: 537714, member: 21346"] Assuming there are no common mode currents present, a tuned electrical half wavelength feed line will faithfully recreate the conditions for X and R at the load (antenna). Any other point along the feed line will have differing values for X and R. If you are limited to SWR, any point along the feed line will show the same SWR, so if you have such a limit, an electrical half wavelength tuned feedline will do you no good. Taking this a step further, many people think that simply because the X and R variables change that SWR will also change, when in fact, the relationship between X and R variables and SWR is such that on a half electrical wavelength of feed line every possible value combination of X and R for a given SWR will be present, and thus SWR is maintained, no matter where on the feed line the measurement is taken. Further, if you know the electrical length of the feed line at the given frequency, it is possible to calculate what X and R are at the load itself. All of this is not taking attenuation into account which on a half electrical wavelength of feedline will generally be very small, if it is noticeable at all. [URL='http://hittman.us'][COLOR=#000000]The DB[/COLOR][/URL] [/QUOTE]

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