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Lucas
KN4MEJ asked if I would have a look at a 1:2.5 balun
and this is what I have come up with.
The
balun is to feed a balanced antenna from an un-balanced line with a
impedance step up from 50ohms to 125ohms, a 1:2.5 Voltage
balun design using a FT140-43 ferrite toroid cores.
It would be advised to have a 1:1 choking balun inline on the
50Ohm side to mitigate the possibility of common mode currents similar
to https://vk6ysf.com/balun_choke_balun_hf_reisert.htm
Construction
The
1:2.5 voltage balun has 4 and 6 turns wound evenly around the
FT140-43
ferrite toroid core with the five individual windings wound close together.
Figure 1 Schematic of the 1:2.5 Voltage balun
Figure
2 Wiring of the 1:2.5 Voltage balun.
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Type
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Voltage Balun
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Ratio
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1:2.5
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Frequency Range
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0.5 ~ 30MHz
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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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4 x 2 and 6 X 2
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SWR
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Low
1:1.2 (1.8MHz) High 1:2.5 (30.0MHz)
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PEP Power Handling.
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Approximately 100W
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Photo 1 1:2.5 Voltage balun
assembled.
The
evaluation of the efficiency of the balun over the desired bandwidth
(0.5 - 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 plot views a 125ohm 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 produced about a 1:1 SWR
The
performance of the balun from 0.5MHz to about 30MHz is good and shows
little reactance, however there is a gradual rise in reactance above
30MHz along with a gradual rise in the SWR.
Figure
3 SWR
data
from the AIM 4170C antenna analyser
plot viewing a 125ohm resistive load through the voltage balun.
Note the 125ohm resistor appears as 50ohms due to the 2.5:1 balun ratio
resulting in an ideal SWR of 1:1.
Figure 4
Impedance data
from the AIM 4170C antenna analyser
plot viewing a 125ohm resistive load through the voltage balun.
Note the Rs = Resistance, Xs = Reactance, Zmag = Impedance
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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