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CHOKING BALUN FOR
HF BANDS
Inline Reisert Choking balun
for HF and upper MF bands. (0.5MHz - 60MHz). FT140-43 Ferrite Toroid Core
To isolate the potential feed-line common mode RF on the coax cable for HF/MF bands ranging from
0.5MHz to 60MHz, a choking balun is required. A ferrite toroidal core with a simple coax cable wound onto it was chosen for this purpose.
Using a choking balun helps prevent unwanted RFI by eliminating feed-line common mode currents and radiation. It ensures that all power is directed to the antenna, improving efficiency. Additionally, it reduces noise or EMI picked up by the coax shield and balances the power between the driven elements of the antenna.
The use of a choking balun
will help mitigate the below issues:
-
Prevents
unwanted RFI by eliminating feed-line 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
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Type
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Choking Balun
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Ratio
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1:1
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Frequency Range
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0.5 ~
60MHz
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Choking Impedance
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1k Ohms
(-20dB) min to
>10k Ohms (-40dB) Ref:
Figure 3
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Core Used
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FT140-43
Ferrite Toroid Core
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Number of turns
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19 (9.5 + 9.5). Ref:
Figure 2
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SWR
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1:1 Ref: Figure 5
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Figure
2 Winding details of the 1:1 choking balun
Construction
The construction simply involved winding 9.5 turns of RG316 coax with a crossover and an additional 9.5 turns onto an FT140-43 Ferrite Toroid Core. This arrangement resulted in a total of 19 turns, which achieved an average lumped value inductive reactance of 40uH to common mode RF currents across a frequency range of approximately
0.5MHz to 60MHz.
Parts
list.
Photo
1 Choking
balun assembled.
Photo
2
Choking
balun assembled.
Testing
The
chart shown in Figure 3, using s Nano VNA antenna analyzer, indicate the attenuation measured in the coax shield. The results demonstrate a minimum attenuation of
-20dB at 0.5MHz, reaching -25dB at 60MHz. Moreover, there is even greater attenuation of better than -40dB observed in the frequency range of
2.5MHz to 12MHz.
Figure
3 The evaluation of the choking attenuation of the balun over a bandwidth
from 0.5MHz- 60MHz.
Figure
4 Choking impedance to dB of choking. 20dB attenuation should be considered the minimum.
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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OF PAGE
Page initiated 08 May, 2025
Page
last revised 08 May, 2025
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