Paul,
Not really of the don't care about SWR camp and I have the
instrumentation to measure all the parameters you mention, It's just
that for those not versed in transmission line theory - SWR is probably
the last parameter which one should concern themselves with.
Paul Christensen wrote:
>> Short answer is the only thing SWR is good for is determining at what
>> point the RF voltages induced by the mismatch will damage your
>> transmitter system. This is why modern rigs fold back transmitter
>> power when excessive SWR is detected, This keeps the voltage developed
>> at a low enough level to prevent damaging the finals.
>>
>
> I think the importance VSWR in HF multiband operation lies somewhere in
> between extreme views. I need to know three things before I become
> worried about VSWR: (1) line characteristic Z; (2); the matched line loss
> spec in dB/ft.; and (3) antenna input terminal Z range. If I know these
> answers, I can then compute VSWR and determine systematic loss due to a
> combination of VSWR and the manufactures specified matched line loss in
> dB/ft. Also, when I know these answers, I can compute an optimum line
> length for maximum power transfer from the transmitter into the line when
> the line characteristic Z is not equal to the antenna input Z.
>
> What bothers me about the "who cares about VSWR" crowd is that they are
> often ignoring total system losses as a result of unknown VSWR, unknown
> matched line loss, and transfer loss between the Tx and line. Even if my
> line had zero loss, the resulting Z seen at the TX end of the line can make
> power transfer inefficient from the rig into the line.
>
> It doesn't take much to get close to reasonable values of line VSWR (and
> only then say "who cares about VSWR") and input Z at the Tx side of the line
> to make the system reasonably efficient. But I would not want to hide my
> head in the sand and use some random length of line, and some random length
> of antenna -- and expect my transmatch to efficiently create a conjugate
> match. The system may be tuned and resonated for reactance cancellation,
> but wouldn't it also be nice to know how much was lost in the process? If
> the answer is yes, then you need to know more about the antenna system
> especially the line Z to antenna Z mis(match) and specified matched line
> loss.
>
> Paul, W9AC
>
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