BLTplus Measurements and Modeling

Hendricks QRP Kits Balanced Line Tuner Plus Measurements and modeling.

All Equipment


Measuring Inductance with RigExpert AA-54

Transformer winding inductance values are measured with a RigExpert AA-54 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
AntScope L Measurement


Figure 2 - T106-2 Transformer Measurement
T106-2 transformer


Table 1 - Transformer Inductance Values
ValueL nH
L13640
L22280
L3890
L1 with L2 short860
L1 with L3 short1940
Laid L1 + L211000
Lopp L1 - L2920
Laid L1 + L37050
Lopp L1 - L32110

Measuring T106-2 Transformer Coupling Factor k

Two measurement methods are used to measure the transformer coupling factor k, secondary open-short approximation and Series-adding Series-opposing. The secondary open-short approximation can be used with high Q transformer inductors.


The formula for the secondary open-short method is:

k = SQRT(1 - Lshort / Lopen)

The formulas for Series-adding Series-opposing method are:

M = (Laid - Lopp) / 4
k = M / SQRT(L1 * L2)

Coupling Factor k using secondary open-short approximation method:

k12 = SQRT(1 - 860 / 3640) = 0.874
k13 = SQRT(1 - 1940 / 3640) = 0.683

Coupling Factor k using Series-adding Series-opposing 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 T-Pad 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
AA-54 SWR
Figure
7.1KX3 10WHigh517.50.26 dB2500.22 dB 45
7.1KX3 10WLow517.50.54 dB2500.58 dB 67
14KX3 10WLow500.19 dB2000.20 dB 89
14XG3 -73 dBmLow500.21 dB2000.20 dB 89
14KX3 10WLow1000.20 dB2000.20 dB 1011


Figure 3 - 517.5 Ohm Load
Load


Figure 4 - High Z setting 517.5 Ohm Load SimSmith Model
SS High Z


Figure 5 - High Z 417.5 Ohm Load AA-54 SWR
High Z AA-54 SWR


Figure 6 - Low Z setting 517.5 Ohm Load SimSmith Model
SS Low Z


Figure 7 - Low Z 417.5 Ohm Load AA-54 SWR
Low Z AA-54 SWR


Figure 8 - Low Z setting 50 Ohm Load SimSmith Model
SS 50 Low Z


Figure 9 - Low Z 50 Ohm Load AA-54 SWR
Low Z 50 Ohm AA-54 SWR


Figure 10 - Low Z setting 100 Ohm Load SimSmith Model
SS 100 Low Z


Figure 11 - Low Z 100 Ohm Load AA-54 SWR
Low Z 100 Ohm AA-54 SWR


Copyright 2014 John Oppenheimer KN5L