[Elecraft] K3 SWR Accuracy - reprise

[Steve Ellington]

"But you cannot transform anything other than a 50 ohm feed point into
a 50 ohm termination by using a 50 ohm transmission line.  (Unless the
line is infinitely lossy.)"
Don't worry....It will be!


Steve
N4LQ
N4LQ at carolina.rr.com
----- Original Message ----- 
From: "Kok Chen" <chen at mac.com>
To: "Steve Ellington" <n4lq at carolina.rr.com>
Cc: "Elecraft Reflector" <elecraft at mailman.qth.net>
Sent: Wednesday, November 04, 2009 8:51 PM
Subject: Re: [Elecraft] K3 SWR Accuracy - reprise


>
> On Nov 4, 2009, at 5:05 PM, Steve Ellington wrote:
>
>> It's called a transmission line transformer and is very common.
>
> Yes, we all know about them.  Just walk 180 degrees on a constant SWR
> circle on the Smith Chart, with the transmission line impedance at the
> center of the Smith Chart (or use 1/4 wavelength in the Telegrapher's
> Equation).
>
> But this is what you'd stated (I am not changing a single word):
>
>> 4. Example: A full wave dipole center fed with 50 ohm coax.
>
> You can use a 600 ohm transmission line to transform a high impedance
> to get a reasonably close match to 50 ohms because the impedance at
> the center of that dipole is *not* infinite but some large number
> (W8JI has good estimates in the Zepp article on his web site).
>
> But you cannot transform anything other than a 50 ohm feed point into
> a 50 ohm termination by using a 50 ohm transmission line.  (Unless the
> line is infinitely lossy.)
>
> It should be obvious from the Smith Chart -- constant SWR circles
> won't hit 50+j0 unless the SWR circle itself has 0 radius (i.e., SWR =
> 1.0:1)
>
> 73
> Chen, W7AY
>
>


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