Rohde & Schwarz UPD, Application Note

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1GA16_1L.DOC ROHDE & SCHWARZ 18
5.1.7 Tuning Frequency
The tuning frequency is the frequency at which the impedance curve shows the first minimum after the
resonance frequency at increasing frequencies. It can be read directly from the impedance curve with the
aid of the graphics cursor. In the program it is obtained by scrolling up through the impedance data array,
starting at fr; the minimum is considered found if N RU 1 (see section 5.1.2, Special Notes on
Entry of Parameters) are found in successive values in the increasing direction.
5.1.8 Q Factor
The quality factor Qt is derived from the impedance curve according to the following formula (BASIC
syntax):
Qt=Fr/(F2-F1)/R0
*
SQR(R0^2-R1^2)/SQR(R1^2-1)
where
Zr, Fr = Resonance impedance and resonance frequency (see section 5.1.5)
Zt, Ft = Tuning impedance and tuning frequency (see section 5.1.7)
R0 = Resonance impedance standardized to RDC (see section 5.1.3, DC Impedance)
R0=Zr/RDC
R1 = Impedance standardized to RDC between Zr and Zout (see section 5.1.7, Tuning Frequency);
R1=SQR(R0)
F1 = Frequency below the resonance frequency at which impedance Z1=R1
*
RDC
F2 = Frequency above the resonance frequency at which impedance Z2=R1
*
RDC
Rdc
Zr
fr
f
Z(f)
f1 f2
Z1~Z2
Zt
ft
FIG 8: Parameters of impedance curve for determining Qt