[Amps] Input SWR revisited

[Robert Carroll]

I suggest a look at this non-mathematical
paper---assuming this list supports links.

Forward and Reflected Power
<http://www.advanced-energy.com/upload/File/White_Paper
s/SL-WHITE7-270-01.pdf> 

You can make the radio happy, but if there are
reflections off the load because the complex load
impedance does not match the characteristic impedance
of the line, there will be standing waves in the
transmission line, leading to more loss than when
feeding a matched load.  For short runs this is a "so
what" but in long lines at higher frequency it can
result in much more loss than would be expected. That's
why when driving highly mismatched loads 450ohm open
wire is often used as it has much lower excess loss due
to SWR on the line than does coax.

 

If you dig this info is in the ARRL handbook and in
more mathematical detail in transmission line and some
electromagnetic books.  You will see that transmission
over a lossless line follows a circle around the Smith
chart but with a lossy line a spiral is followed.  If
the line is long enough the spiral continues to the
center of the chart. 

Bob W2WG

 

-----Original Message-----
From: Amps [mailto:amps-bounces at contesting.com] On
Behalf Of donroden at hiwaay.net
Sent: Wednesday, January 14, 2015 5:13 PM
To: amps at contesting.com
Cc: amps at contesting.com
Subject: Re: [Amps] Input SWR revisited

 

> But, the swr inside the 75 ohm coax is still 1.333 at
all points along 

> the cable.

 

No, not at either end.

 

Why does the swr "inside" the coax even matter when we
are discussing load and source impedances ?

 

 

Don W4DNR

 

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