[Elecraft] Measuring SWR (Long)

[W2xj]

I agree except that even at 500KW a 2:1 or greater is the norm with open wire line. 

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> On Apr 9, 2019, at 19:10, Fred Jensen <k6dgw at foothill.net> wrote:
> 
> Well, the reflected power is created by a "virtual transmitter" at the feedpoint of the antenna and heads down the coax which has a surge impedance of Z0 ohms.  It meets the SO-239 at the TX and sees an impedance of Z1, the impedance presented by the PA and output filters.  If Z1=Z0, the power is dissipated as heat in the PA and associated RF circuitry.  If Z1<>Z0, some is dissipated and some is reflected, where some is radiated, and some is reflected [virtual transmitter again].  Ad infinitum, and when forever is over, it is all gone and everyone lives happily ever after.
> 
> SWR and all the associated measuring equipment and concern with it only became an issue when: 1) Coax replaced parallel lines and; 2) Resonant output circuits were replaced by solid state amplifiers with non-resonant filters.  When I sat for the Extra in early 1956, the only question that involved standing waves was one about how Lecher Lines could be used to measure transmitter frequency.
> 
> It's important today but calculating it hasn't changed.  At 10 W, a 2:1 SWR will probably work ok.  At 1500 W, a solid state amplifier may not be happy with the voltages developed at its output connector.
> 
> 73,
> Fred ["Skip"] K6DGW
> Sparks NV DM09dn
> Washoe County
> 
>> On 4/9/2019 5:56 PM, Don Sanders wrote:
>> Since no one has answered your question. I will venture a
>> supposition that many know but few will speak out.
>> And some still remember their CB days and the erroneous
>> advertising saying the power is lost.
>> Reflected Power flows back down the feed line and is subjected
>> to the normal feed line loss. It then is "reflected" back toward the
>> antenna, again subject to the feed line loss, where some of it is
>> radiated and some reflected again.
>> This continues until the power is dissipated. The book "Reflections"
>>  has a very good but somewhat technical explanation.
>> Therein also is the reference to forgetting about striving for the
>> "Holy Grail" of 1:1 SWR.
>> And concentrating on getting it low enough that the transmitter will
>> supply full power output. Also using the best low loss feed line and
>> proper matching when possible of the feed line to the antenna.
>> 
>> Dr. Don W4BWS
>> 
> 
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