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CHOKING BALUN FOR HF BANDS

Choking balun for HF and upper MF bands. (1.5MHz - 30MHz).


Requiring a choking balun to isolate the potential feed-line common mode RF on the coax cable for HF/MF bands 1.5MHz - 30MHz. A simple coax cable wound on to a ferrite toroidal core was chosen.

  • Prevents unwanted RFI by eliminating feedline common mode currents and radiation
  • All power goes to the antenna, improving efficiency
  • Reduces noise or EMI picked-up by your coax shield
  • Power is balanced between driven elements of antenna

 

 

 

Figure 1 Schematic of the 1:1 choking balun  

 

Type  Choking Balun
Ratio 1:1
Frequency Range 1.0 ~ 30MHz
Choking Impedance 1k Ohms (-21dB) minimum. Ref: Figure 3
Core Used FT240-43 Ferrite Toroid Core
Number of turns 14 (7 + 7). Ref: Figure 2
SWR 1:1 Ref: Figure 5

 

 

 

Figure 2 Winding details of the 1:1 choking balun  

 

Construction

 

The construction was simply to wind 14 turns of RG58 coax onto a FT240-43 Ferrite Toroid Core. The result of 14 turns achieved an average of 40uH lumped value inductive reactance to common mode RF currents from approximately 1.0MHz to 30MHz.

Parts list.

  • FT240-43 Ferrite Toroid Core
  • About 1.0mtr of RG58 coax.

 

Photo 1 Choking balun assembled

 

 

 

 

Testing

 

The AIM 4170C antenna analyser recorded in Figure 3 show the Impedance as measured in the coax shield presents a minimum of 1000 Ohms from 1.0MHz to about 30MHz and much greater for the 1.8MHz to 14MHz amateur radio bands.

 

Figure 3 The evaluation of the choking impedance of the balun over a bandwidth from 1.0MHz- 30MHz.

 

 

Figure 4 Choking impedance to dB of choking. 20dB attenuation should be considered the minimum.

 

 

Figure 5 SWR.from 0.1MHz- 30MHz

 

 

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 02 January 2022  
 

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