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1:4 GUANELLA CURRENT BALUN - HF

1:4 Guanella Current Balun for HF and  MF bands. (0.3MHz - 30MHz).


Requiring a balun to feed a balanced feed line from an un-balanced T-Match tuner, a 1:4 Guanella Current balun design using a single FT240-43 ferrite toroid cores was selected. An impedance transformation balun is required due variations in impedances that are nearly always on the higher side of the nominal 50 ohms when feeding a multi-band balanced antenna system. The balun may be required to sep up the feed impedance presented at the T-Match tuner to improve the matching range.

 

Construction

 

The 1:4 current balun consists of two double bifilar winding of 11.5 turns wound evenly spaced around the FT240-43 ferrite toroid core as shown in figure 2.

 

 

Figure 1 Schematic of the 1:4 Guanella Current balun.

Type  Impedance transformation
Ratio 1:4
Frequency Range 1.5 ~ 30MHz
Core Used FT240-43 Ferrite Toroid Core
Number of turns a = 11.5 tuns plus b = 11.5 turns
SWR 1.2:1 or less. Ref: Figure 3

 

 

Figure 2 Wiring of the 1:4 Guanella Current balun.

Note this drawing shows winding connections and not the number of turns required. See article for details.

 

Parts list.

  • 1 x FT240-43 ferrite toroid core.

  • 4 x 800mm of PTFE silver plated copper wire, 1.0mm, AWG 18, WHITE

 

Testing

 

The AIM 4170C antenna analyser recorded the balun impedance transformation efficiency a for a frequency range from 1.0MHz to 30MHz.

 

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 of the balun using a AIM 4170C antenna analyser. The efficiency is shown to be relatively flat from below 1.0MHz to above 30MHz. The below antenna analyser plot viewing a 200ohm resistive load attached to the balanced side of the balun and measured at a nominal impedance of 50ohms presented as anticipated an approximate 50ohm load to the analyser and ideally produced about a 1:1 SWR. The results are a little higher than expected, however demonstrates that the balun's 1:4 current transformation occurs reasonably efficiently from well below 1.0 to beyond 30MHz 

Figure 3  AIM 4170C antenna analyser plot viewing a 200ohm resistive load through the Guanella current balun. Note the 200ohm resistor appears as 50ohms due to the 1:4 balun ratio resulting in an ideal SWR of 1:1. This plot shows an SWR ranging from 1.0:1 to about 1.2:1

Figure 4  AIM 4170C antenna analyser plot viewing a 200ohm resistive load through the Guanella current balun. Note the 200ohm resistor appears as 50ohms due to the 1:4 balun ratio. The Rs (Resistive load) tracks closely with Zmag as would be hoped with the Xs (Reactive load) being relatively low. 

 

Also see other baluns and ununs:

1:1 Choking balun Choking balun for lower HF and MF bands. (1.8MHz - 10MHz) T250-26 Powdered Iron Toroid Core.

1:1 Choking balun low band VHF Choking balun for lower band VHF. (14 ~ 54MHz) FT140-43 Ferrite Toroid Core.

1:1 Guanella current balun 1:1 Guanella current balun (1.8 - 30MHz) L15 ferrite toroid core.

1:4 Guanella current balun 1:4 Guanella current balun (1.8 - 30MHz) L15 ferrite toroid core.

1:1 Ruthroff voltage balun, 1:1 Ruthroff voltage balun (1.8 - 30MHz) T-200-2 powdered iron toroid core.

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

6:1 Ruthroff voltage balun  6:1 Ruthroff voltage balun (1.8 - 30MHz) L15 ferrite toroid core.

1:9 voltage unun_v1  9:1 voltage unun (1.8 - 30MHz) T-200-2 powdered iron toroid core. Version 1 

1:9 voltage unun_v2  9:1 voltage unun (1.8 - 30MHz) L15 ferrite toroid core. Version 2

 

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Page last revised 20 November 2019  
 

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