Page 71 - RTH3BA Preview
P. 71
41 - ����������� - AC ��������
In other words, the antenna has a complex impedance of 28j208Ω and does the L-
match convert this to 50j0Ω at the transmitter to give near 1:1 VSWR?
Figure 41-24 Circuit of antenna tuner and it’s load
This L-match has been adjusted for low SWR and then the values of L and C read
with an LCR meter. Can we prove using complex number arithmetic that the L-match
is converting the antenna impedance of 28j209Ω to 50j0Ω, as seen by the
transmitter?
The first step is to convert the 67.47pF capacitance and the 0.87µH inductor to their
respective reactances so that we can re-draw the circuit with impedance only.
X C= 1/2πfC
X C= 1/2π x 10.1MHz x 67.47pF
X C = 233.55Ω and we write this as 0-j233.55Ω
X L= 2πfL
X L= 2π x 10.1MHz x 0.87µH
X L = 55.21Ω and we write this as 0+j55.21Ω
Next, we re-draw the circuit and update the L and C with their equivalent reactances
at 10.1MHz.
Figure 41-25 Figure 41-25 converted to reactances
PREVIEW
617
