In a message dated 98-07-06 07:02:26 EDT, you write:
<<
In a case like the beam, where the resistive impedance may be in the 20-30
ohms range, and the required capacitive reactance for a beta match may be
also in the 20 to 30 ohms range, the SWR will be well over 2:1, and the
impedance along the 50-ohm line will change its R and X values fairly
rapidly. Hence, the need for a well-calibrated 1/2 wl line to determine
the load values accurately.
Hope this is useful.
-73-
LB, W4RNL >>
Hi LB,
Thanks. You are correct of course when measuring complex impedance. In that
case only a line of zero or a multiple of 1/2 wl, or SWR of 1:1 will present
correct results and only at or very close to one frequency.
RESONANCE (zero reactance crossing) can be directly measured if the line is
zero length or a multiple (even or odd) of 1/4 wl, or if SWR at resonance is
1:1.
Like the quarter wave line, the half wave line is the correct length at only
one frequency in the band of interest.
The new analyzer contains two software functions I disagreed strongly with
including, because they cause confusion like this. One is mismatch loss (or
percent transmitter power or match efficiency in some units, I missed that
thread while putting up my new very high 160 meter dipole --- what luck !!)
the other is a resonance mode.
I explained away those functions by pretty much saying they don't mean much
and can be confusing to nearly any user. From this thread, I see my worryment
was correct! I'll now push harder to have them removed.
The last thing I want to see is someone thinking 32% transmitted power means
most of his power is not being radiated, or that zero reactance measured some
distance from the feedpoint (by itself) means the antenna is resonant.
73 Tom
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