[Elecraft] Remote Antenna Tuner

[Jack Brindle]

On Sunday, September 7, 2003, at 07:46  PM, Vic Rosenthal wrote:

> The difficulty of matching an antenna is determined by the impedance  
> that tuner sees, not the SWR.  Although the SWR is (almost) exactly  
> the same regardless of the line length (measured SWR drops a bit as  
> lines get longer because of losses), the impedance varies cyclically  
> as you change the length of the line.  So if the impedance at the  
> antenna feedpoint is 2000 ohms, the impedance seen by the tuner will  
> be 2000 ohms only when the feedline is a multiple of exactly 1/2  
> wavelength. The tuner may have trouble with very high or low  
> impedances, but you can easily avoid problems by changing the length  
> of the line slightly.  So the answer is that it is quite easy to feed  
> an antenna through a line with a 50:1 SWR as long as you avoid some  
> problematic lengths.

Unless you are using hardline or some other ultra-low-loss coax, this  
high of an SWR will result in very little signal getting to the  
antenna, and probably very short life of the coax. Coax loss is  
generally dissipated as heat in the insulator between the center  
conductor and shield. 100 watts at 20:1 or higher SWR makes a short  
life of RG58.

I'll stick with my ultra-low loss open wire feed and balanced tuner,  
thank you. I really don't care what the SWR is on the feedline, because  
there is virtually no loss - all of my signal gets  to the antenna. I  
get the added benefit of very interesting signal lobes on 15 and 10  
meters that make the antenna extra useful.

- Jack Brindle, WA4FIB
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