1:6 voltage balun using a FT140-43 Ferrite Toroid Core for 0.5MHz to 30MHz. Completed January 2022.

Requiring a balun to feed a balanced antenna from an un-balanced line with a impedance step up from 50ohms to 300ohms, a 1:6 Voltage balun design using a FT140-43 Ferrite Toroid Core was selected.

Construction

The 1:6 voltage balun has 6 x 2 and 4 X 2 turns 0.5mm2 hook-up wire wound evenly spaced around the FT140-43 Ferrite Toroid Core. See Figure 2 and Photo 1 for details.

Figure 1 Schematic of the 1:6 Voltage balun  

Figure 2  Wiring of the  1:6 Voltage balun.

Photo 1 1:6 Voltage balun assembled. 

The evaluation of the efficiency of the balun over the desired bandwidth (1.0 - 30MHz) was carried out by testing the impedance that could be seen from unbalanced side to a resistive load applied to the balanced side using an AIM 4170C antenna analyser. The below antenna analyser graph shows a 300ohm resistive load attached to the balanced side of the balun and measured at a nominal impedance of 50ohms that should presented an approximate 50ohm load to the analyser and produced about a 1:1 SWR

The performance of the balun from 0.5MHz to 30MHz is good and shows little reactance, however there is a gradual rise in reactance above 10MHz along with a gradual rise in the SWR. Despite this rise in reactance and SWR the balun should still perform well.

Figure 3  SWR. AIM 4170C antenna analyser data graph viewing a 300ohm resistive load through the voltage balun from 0.1MHz to 30MHz. Note the 300ohm resistor appears as 50ohms due to the 1:6 balun ratio resulting in an ideal SWR of 1:1. The SWR is shown to be consistently low for all Amateur radio bands with a high of just 1:1.7 for the 10m band.

Figure 4 Impedance The AIM 4170C antenna analyser data graph viewing a 300ohm resistive load through the voltage balun from 0.1MHz to 30MHz. Note the 300ohm resistor should ideally appears as 50ohms due to the 1:6 balun ratio.

Figure 5 Impedance (R & X). AIM 4170C antenna analyser data graph viewing a 300ohm resistive load through the voltage balun from 0.1MHz to 30MHz. Note the 450ohm resistor should ideally appears as 50ohms due to the 1:6 balun ratio. The impedance should ideally be R (Resistance) at 50 ohms and X (Reactance) near zero ohms. The Purple line shows the resistance component in ohms of the Impedance and the Orange line shows the reactive component in ohms of the Impedance, the + values for the reactance represent Inductive reactance and the negative values represent the Capacitive reactance.

Conclusion

The Version 2 1:6 voltage balun using a FT140-43 Ferrite Toroid Core represents a very efficient balun for a frequency range from 0.5MHz to 30MHz at a power level of 100W PEP.

Power Handling 

For Summary of suitable ferrite cores and core types for a frequency range of 100 kHz to 50 MHz for power levels of 50W, 100W, and 500W continuous and SSB. It assumes good thermal management and proper balun design. See: Power - Ferrite Core Design

Also see other baluns and ununs:

BALUN 1:1 CHOKE & 1:4 BALUN  HF ladder feed-line to coaxial cable combination choke and 1:4 balun. (0.1MHz - 30MHz). 

BALUN 1:1 CHOKING Choking balun for lower HF and MF bands. (200kHz - 10MHz).

CHOKING 1:1 BALUN - HF BANDS Reisert choking balun. (1.0MHz - 30MHz). FT240-43 Ferrite Toroid Core.

CHOKING 1:1 BALUN - HF BANDS Reisert choking balun (1.5MHz - 30MHz). FT140-43 Ferrite Toroid Core.

CHOKING 1:1 BALUN - LOW VHF BAND Choking balun. (10MHz - 60MHz). FT140-43 Ferrite Toroid Core.

BALUN 1:1 CURRENT 1:1 Guanella Current balun using a L15 ferrite core (1.8 - 30MHz).

BALUN 1:4 CURRENT 1:4 Guanella Current balun using a L15 ferrite core (1.8 - 30MHz).

BALUN 1:4 SINGLE CORE CURRENT 1:4 Guanella Current Balun, single FT240-43 ferrite toroid cores. (0.3MHz - 30MHz). 

BALUN 1:1 VOLTAGE 1:1 Ruthroff voltage balun using a T-200-2 powdered iron toroid core  (1.8 - 30MHz).

BALUN 4:1 VOLTAGE 4:1 Ruthroff voltage balun using a T-200-2 powdered iron toroid core  (1.8 - 30MHz).

BALUN 6:1 VOLTAGE - VERSION 1 6:1 Voltage balun using a L15 ferrite toroid core  (1.8 - 30MHz).

BALUN 6:1 VOLTAGE - VERSION 2 6:1 Voltage balun using a FT140-43 Ferrite Toroid Core  (1.8 - 30MHz)

BALUN 9:1 VOLTAGE - VERSION 1 9:1 Voltage balun using a L15 ferrite toroid core  (1.8 - 30MHz).

BALUN 9:1 VOLTAGE - VERSION 2 9:1 Voltage balun using a FT140-43 Ferrite Toroid Core  (0.5 - 60MHz).

UNUN 9:1 VOLTAGE 9:1  voltage unun using a T-200-2 powdered iron toroid core  (1.8 - 30MHz). 

UNUN 9:1 VOLTAGE VERSION 2 9:1  voltage unun using a L15 ferrite core (1.8 - 30MHz). 

UNUN 9:1 VOLTAGE VERSION 3 9:1  voltage unun using a FT140-43 ferrite core (0.5 - 60MHz).

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Page last revised 05 May, 2025