A followup to my earlier post about coaxial line capacitors:
Resistive loss in coaxial stubs, used as capacitors, inductors, or
whatever, is an unavoidable consequence of the attenuation present
in any transmission line. When the stub is used as a gamma capacitor,
this resistance appears in series with the antenna's feed point
resistance. If you are comfortable with Smith chart calculations,
you can calculate the resistance component presented by a stub
of any length if you know the line attenuation specification.
Rather than give the procedure here, refer to the ARRL Antenna
Handbook chapter on Smith chart calculations. In my 1994 edition,
the discussion starts on page 28-6, under the section "Line-Loss
Considerations with the Smith Chart." These calculations predict
very accurately the resistive losses I measure directly, although a high
quality impedance bridge is required to make the direct measurement.
73, John W1FV
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