BLTplus Measurements and Modeling
Measuring Inductance with RigExpert AA54
Transformer winding inductance values are measured with
a RigExpert AA54
and AntScope.
Each inductance value is an average of several measurements near Z =
50 Ohm. The Agilent
Application Note has accuracy considerations for the
Transmission/Reflection inductance measurement technique. A typical
AntScope view is shown in Figure 1. OSL
calibration was performed at the BNC to Banana adapter posts. The
transformer is shown in Figure 2. The
inductance values for the two BLTplus transformer ratios are shown in
Table
1.
Figure 1 
Typical AntScope Inductance Measurement



Figure 2 
T1062 Transformer Measurement



Table 1 
Transformer Inductance Values


Value  L nH


L1  3640
 L2  2280
 L3  890
 L1 with L2 short  860
 L1 with L3 short  1940
 Laid L1 + L2  11000
 Lopp L1  L2  920
 Laid L1 + L3  7050
 Lopp L1  L3  2110


Measuring T1062 Transformer Coupling Factor k
Two measurement methods are used to measure the
transformer coupling factor k, secondary openshort approximation and
Seriesadding Seriesopposing. The secondary openshort approximation
can be used with high Q transformer inductors.
The formula for the secondary openshort method is:
k = SQRT(1  Lshort / Lopen)
The formulas for Seriesadding Seriesopposing method are:
M = (Laid  Lopp) / 4
k = M / SQRT(L1 * L2)
Coupling Factor k using secondary openshort approximation method:
k12 = SQRT(1  860 / 3640) = 0.874
k13 = SQRT(1  1940 / 3640) = 0.683
Coupling Factor k using Seriesadding Seriesopposing method:
M12 = (11000  920) / 4 = 2520
k12 = 2520 / SQRT(3640 * 2280) = 0.875
M13 = (7050  2110) / 4 = 1235
k13 = 1235 / SQRT(3640 * 890) = 0.686
Performance Measurements
Loss measurements were performed with an Elecraft KX3,
DL1 Dummy Load, and XG3 RF Signal Source.
The 517.5 Ohm (measured DC R) load includes four series parallel 470
Ohm resistors as shown in Figure 3. Loss
measurement and SimSmith model loss
values are shown in Table 2. The SimSmith
models include a resistor in series with the transformer primary to
model transformer primary Q and a 0.1 dB TPad to account for constant
loss.
Table 2 
Loss Values


Frequency MHz
 Power
 Z Setting
 Load Ohm
 Measured Loss
 Applied Transformer Q
 SimSmith Model Loss
 SimSmith Figure
 AA54 SWR Figure
 7.1  KX3 10W  High  517.5  0.26 dB  250  0.22 dB
 4  5
 7.1  KX3 10W  Low  517.5  0.54 dB  250  0.58 dB
 6  7
 14  KX3 10W  Low  50  0.19 dB  200  0.20 dB
 8  9
 14  XG3 73 dBm  Low  50  0.21 dB  200  0.20 dB
 8  9
 14  KX3 10W  Low  100  0.20 dB  200  0.20 dB
 10  11


Figure 4 
High Z setting 517.5 Ohm Load SimSmith Model



Figure 5 
High Z 417.5 Ohm Load AA54 SWR



Figure 6 
Low Z setting 517.5 Ohm Load SimSmith Model



Figure 7 
Low Z 417.5 Ohm Load AA54 SWR



Figure 8 
Low Z setting 50 Ohm Load SimSmith Model



Figure 10 
Low Z setting 100 Ohm Load SimSmith Model



Copyright 2014 John Oppenheimer KN5L