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

Figure 2 - T106-2 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 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	Analyzer 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
14	VNWA	Low	50	0.21 dB				12

Figure 3 - 517.5 Ohm Load

Figure 4 - High Z setting 517.5 Ohm Load SimSmith Model

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

Figure 6 - Low Z setting 517.5 Ohm Load SimSmith Model

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

Figure 8 - Low Z setting 50 Ohm Load SimSmith Model

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

Figure 10 - Low Z setting 100 Ohm Load SimSmith Model

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

Measuring Loss with VNWA Two Port VNA

Figure 12 - VNWA Two Port Measurement