[Amps] Input SWR revisited

[donroden at hiwaay.net]

In practice, few of us run amplifier input cables in the multi-quarter  
wave length category, so spiraling around the Smith is not an option.
Just Saying .......

Don W4DNR




Quoting Robert Carroll <w2wg at comcast.net>:

> 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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