steve at karinya.net
Sun Feb 1 18:03:59 EST 2009
Then if those formulas fall down with the particular values I gave, they
Look at it this way: at HF the losses in feedlines are predominantly
I^2R losses - the higher the current the higher the loss per unit
length. Picture a line terminated in an impedance higher than its
characteristic impedance - for a given power, the current directly at
the load will be lower than if it were terminated with Zo; so the I^2R
losses will be lower per unit length AT THAT POINT.
Now move back a little way along the line from the load. In the
unmatched case the current will rise (because of the standing wave) and
the I^2R losses will begin to increase, whereas in the match case the
current is constant and the losses don't change. At some line length the
sum total of the increasing unmatched losses will equal the sum total of
the matched losses - for any line shorter than this, the unmatched
losses will be less.
For any load impedance greater than Zo there will be some short lengths
of line over which the total loss is less than it would be in the
matched case. Any formula that says otherwise is just an approximation.
Dr. Gerald N. Johnson wrote:
> The formulae on page 24-9 of the 1994 ARRL Antenna Book would always
> show a greater loss than the matched loss of the line. Perhaps the chart
> you are referring to is showing the ADDED loss because of the mismatch?
> TenTec mailing list
> TenTec at contesting.com
More information about the TenTec