Requiring a balun to feed a balanced antenna from an un-balanced load
with an impedance step up from 50ohms to 450ohms, a 1:9 Voltage
balun design using an L15 ferrite toroid cores was selected.
Construction
The
1:9 voltage balun has 5 turns wound evenly spaced around the L15
ferrite toroid core
with the five individual windings wound close together. The toroidal
core was wrapped in an overlapping layer pink
heavy duty Teflon plumbers tape to
protect the enamelled copper wire from insulation puncture from
abrasion with the toroid core.
As
this Balun will be used out in the weather a weatherproof plastic
enclosure is used. See photos 1,2 and 3.
The
entry holes for the SO-239 connector and the binding post have small bead of rubberised silicon sealant to achieve
full waterproofing of the Balun. Photo 2 shows the perfect
application of the rubberised silicon sealant
spread uniformly from under the binding post, which will also give
additional grip if the post were over tightened.

Figure 1 Schematic of the 1:9 Voltage balun

Figure
2 Wiring of the 1:9 Voltage balun.
Note
this drawing shows winding connections and not the number of turns
required. See article for details.
Parts
list.
·
1.25mm
Enamelled copper wire.
- L15
ferrite toroid core. Jaycar
Cat. No. LO-1238
-
Pink
heavy duty Teflon plumbers tape.
- About
3 x 500mm of 1.25mm Enamelled copper wire.
- Two
Gold
Banana Socket Binding Post - Black. Jaycar
Cat. No. PT-0431
- SO-239
UHF chassis mount connector
-
Sealed
Polycarbonate Enclosures 82 x 80 x 55mm from Jaycar
Cat.
No. HB-6230

Photo 1 1:9 Voltage balun
enclosure assembled.
Photo 2 1:9 Voltage balun
enclosure
assembled.
Photo 3 1:9 Voltage balun
assembled in weatherproof enclosure.
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 antenna
analyser. The below antenna analyser plot views a 450ohm 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 1.0MHz to about 30MHz is good and shows
little reactance, there is however a gradual rise in reactance
above 30MHz along with a gradual rise in the SWR. Despite this rise in
reactance and SWR the balun should still perform well up into the
50MHz amateur band.

Figure
3 AIM 4170C antenna analyser
plot viewing a 450ohm resistive load through the voltage balun.
Note the 450ohm resistor appears as 50ohms due to the 9:1 balun ratio
resulting in an ideal SWR of 1:1.
AIM 4170C antenna analyser explanation;
SWR
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Standing Wave Ratio.
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Zmag
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Total Impedance.
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Theta
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Phase angle between voltage and current.
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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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