VE2AZX 1

Radio Talk 2013Jacques AudetVE2AZX Sept. 2013

VE2AZX@amsat.org

VE2AZX 2

- REASONS FOR USING A BALUN

- TYPES OF BALUNS

- CHECK YOUR BALUN WITH AN SWR ANALYZER

- RESULTS

- MESURING THE IMPEDANCE OF A NUMBER OF FERRITES

- IMPEDANCE MEASUREMENT RESULTS

- USING FERRITES ON A FEEDER AND HOUSE CONDUCTORS

VE2AZX 3

REASONS FOR USING A BALUN ?

BALUN = BALanced to Unbalanced - It’s a transformer

Used to feed a balanced load, Ex: dipole

Decreases feeder radiation

The feed line becomes independent of the antenna:

We can change its length … move it around

Without causing SWR change.

VE2AZX 4

REASONS FOR USING A BALUN ?

With a balun, radiation picked up by thefeeder from each side of the dipole cancels at the feeder. This will decrease feedline current.

BALU

N

+ -DIPOLE

The feedline’s outer shield becomes ”floating” and independent of the antenna.

The feedline should run away fromthe dipole at right angle. The dipole should be parallel to the ground.

A non symetrical antenna Ex: Windom…Will require the use of a current balun

VE2AZX 5

BALUN TYPES

VOLTAGE

- TRANSFORMER WITH WINDINGS GIVING A BALANCED OUTPUT

- IN-OUT IMPEDANCES ARE DETERMINED BY THE TURNS RATIO.A WIDE RANGE OF RATIOS IS POSSIBLE.

- OPERATES OVER A SOMEWHAT LIMITED BANDWIDTH (100 TO 1)

CURRENT

- USES TRANSMISSION LINES WOUND ON A CORE

- MAY USE A COAXIAL CABLE OR A PARALLEL WIRE LINE WITH OR WITHOUT FERRITES.

- COMMON IMPEDANCE RATIOS: 1:1 AND 4:1

- OPERATE OVER A MUCH WIDER BAND OF FREQUENCIES

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1:1 VOLTAGE BALUN

- 3 IDENTICAL WINDINGS

- GENERALLY 50 : 50 ohms

Measured Inductance:~13.4 uH

We should have ~ the sameinductance at the input andat the output.

MesuredInductance~13.4 uH

Identical windings

Connected in series

SO-239

1

2

3

4

BALANCEDSIDE

~29.2 µH

~3.3 µH

VE2AZX 7

VOLTAGE BALUN 4:1

- 2 IDENTICAL WINDINGS

SO-239

200 Ώ Identical windings

connected in series

Term

inat

e to

che

ckS

WR

BALANCEDSIDE

INPUT SIDE

The measured inductance at the output is ~ 4X the input inductanceas a result of inductance coupling.

VE2AZX 8

TESTING A BALUN WITH AN SWR ANALYZER

These tests verify:Winding inductance Winding distributed capacitanceThe quality of the insulation between conductors

BALUNSWRANALYZER

Coaxial 50 ohms 50 ohms (balun 1:1)OR:200 ohms (balun 4:1)

Load resistance:

The minimum SWR should be below 1.5 In the middle of the balun’s frequency range

Indicates low losses

VE2AZX 9

CONNECTING THE LOAD RESISTANCE 50 Ω HERE

IT IS IMPORTANT TO USE SHORT and LARGE CONDUCTORS

VE2AZX 101 MHz 10 MHz 50 MHz

BALUN 1:1UNADILLAW2AU

MEA

SUR

ED S

WR

WIT

H A

50

ohm

s L

OA

D

1.0:1

1.5:1

2.0:1

swr

swr

Min SWR ~ 1.1

VE2AZX 11

IMPEDANCEvs

Frequencywith a 50 ohm load

resi

stan

cere

acta

nce

frequ

ency

BALUN 1:1UNADILLAW2AU

50 Ω

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KENPRO KA50

1 MHz 10 MHz 50 MHz

1 :1

2 :1

3 :1

4 :1

5 :1

Min SWR ~ 1.3MEA

SUR

ED S

WR

WIT

H A

50

ohm

s L

OA

D

VE2AZX 13

UNADILLA 4 : 1

1 :1

2 :1

3 :1

4 :1

5 :1

1 MHz 10 MHz 50 MHz

MEA

SUR

ED S

WR

WIT

H A

200

ohm

s L

OA

D

VE2AZX 14

OPEN CIRCUIT TESTS WITH THE SWR ANALYZER

These tests verify:Winding inductance Winding distributed capacitanceQuality of the winding insulation

VOLTAGE BALUN

SWR ANALYZER

50 ohmsCoaxialtee

Coaxial 50 ohms

Opencircuit

The minimum SWR should be below 1.1 in the middle of the balun’s frequency range

Indicates low losses

VE2AZX 15

OPEN CIRCUIT TESTS WITH THE SWR ANALYZER

MEA

SUR

ED S

WR

CH1 S11 SWR 200 m / REF 1

1 MHz 50 MHz

Cor

PRm

SCALE

200 m /div

23 Sep 2003 11:17:02

2 3

4

5

1_: 1.3601

1.8 MHz

2_: 1.1036 3.5 MHz

3_: 1.0999 7.562 MHz

4_: 1.3392 14 MHz

5_: 2.1619 30 MHz

1

50 ohms

BALUN 1:1 or 4:1UNADILLA W2AU

SWR

1.0:1

1.5:1

2.0:1

swr

swr

10 MHz5 MHz

Always 50Ωwhatever the Z ratio

CoaxTee

VE2AZX 16

OPEN CIRCUIT TESTS WITH A VNA

resi

stan

cere

acta

nce

feéq

uenc

y

COMPLEXIMPEDANCEvs Frequency

Shows open circuit betweenaround 5 MHzWinding inductance resonateswith its distributed capacitance

Winding Inductanceat 1.8 MHz

BALUN 1:1UNADILLAW2AU

VE2AZX 17

CURRENT BALUNS

QUESTION: How many independent conductors at RF frequencies do we have in a coaxial cable ? 1, 2, 3 or 4 conductors ?

There are 3 independent conductors: - The center conductor - The inner surface of the shield- The outer surface of the shield

Note that the RF current that flows on the outer surface of the shield is independent of the inner shield current.

This is so because at RF frequencies, the current penetrates very littleinside the conductors. This is called SKIN EFFECT.

Note also that the SWR only applies to the inner shield currents (and center cond).The SWR is basically independent of the outer shield currents.

VE2AZX 18

SHIELDED LOAD

With a shielded load, the current stays inside the coax

There is no current on the outside of the coax, whatever the load (open, shortor terminated)

Adding ferrites on the outside of the coax has NO effect, since no current flows on the outside of the shield.

Shielded loadCurrent flow

Current flow

Coaxial Cable

VE2AZX 19

UNSHIELDED LOAD

A dipole is an unshielded loadAn unshielded load causes current to flow on the outer surface of the coax, since it picks up radiated currents. In fact it is part of the antenna. The radiation pattern changes.

A dipole is anunshielded load

Current flow

Current flow

Coaxial Cable

External current flow Most antennastend to “spray” RFon their feeding coaxtoo.

Current flowing on the outer shield modifiy the basic dipole by adding a third conductor and will generally change its impedance

Note that the inner conductor and inner shield currents are equal.

VE2AZX 20

UNSHIELDED LOAD

Adding a ferrite core adds resistance (at RF) only on the OUTSIDE of the coax.

The ferrite core reduces the shield currents

The ferrite core has NO effect on the internal coax currents, besides restoring the dipole impedance and normal radiation pattern.

Note that the inner conductor and inner shield currents are equal.

Current flow

Current flow

Coaxial CableFERRITECORE

A dipole is anunshielded load

Most antennastend to “spray” RFon their feeding coaxtoo.

Shield currents encounter a high impedance and are attenuated.

VE2AZX 21

CURRENT BALUNS

How much Resistance is Required when Feeding a dipole with a coaxial cable ?

Dipole λ/2Feed point% of end

A coax cable feeds adipole at its center,or with an offset

Dipole λ/2TXEquivalent CircuitThe coax is partof the antenna

λ/4 open stubIs the WORSTlength – since itreflects a short Open circuit stub

For simulation purposes,the TX (source) is verysmall and floating.

VE2AZX 22

CURRENT BALUNSFeeding a dipole with a coaxial cable

Dipole λ/2TX

Balun Equivalent Circuit

What is the minimum value ofImpedance that I can have …

That will have little effect on the gain and impedance of the dipole antenna ?

Balun RF impedance

R

Dipole λ/2TXTo decrease the stub current:A current balun is inserted.It adds a series impedance on the outside of the coax.

Balun(ferrites)

VE2AZX 23

CURRENT BALUNSDipole λ/2

R

λ/4Feeding a dipole with a coaxial cable

DIPOLE IMPEDANCE VS LOAD R

0

20

40

60

80

100

120

140

1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06

50 % OFFSET Z dipole at resonance33 % OFFSET Z dipole at resonance

R in ohms

Ω

DIPOLE IMPEDANCE

CENTER FEED

33 % OFFSET

DIPOLE AVERAGE GAIN VS LOAD R

-3

-2

-1

0

1

2

3

1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06

50 % OFFSET Z dipole at resonance33 % OFFSET Z dipole at resonance

R in ohms

AVERAGE DIPOLE GAIN

dB

33 % OFFSET

CENTER FEED

If feeding at the center (50%): R > 1000 ohmsIf feeding at 33% from end: R > 10000 ohmsIt’s easier to feed at the center

VE2AZX 24

CURRENT BALUNS1:1 CURRENT BALUN

FERRITES COAX

ANTENNA

Z - Ferrites

1 : 1Ideal TransformerEquivalent

Circuit at RF

The RF resistance caused by the ferrite impedance should be high ( > 1000 ohms)- To minimize the RF transmitted and received

by the feeder.- Minimize temperature increase in the ferrite

at high power by using Z ferrite > 5000 ohms.

Balanced Antenna

VE2AZX 25

FERRITE IMPEDANCE

DEPENDS ON…

- MATERIAL

- LENGTH

- VOLUME OF MATERIAL

- VARIES WITH FREQUENCY

- TO CALCULATE THE IMPEDANCE Z: (approx.)

IMPEDANCE OF ONE TURN FOR ONE FERRITEmultiplied by…

NUMBER OF FERRITESmultiplied by …

(NUMBER OF TURNS) squared

- NOTE: 1 TURN = FERRITE ON A STRAIGHT WIRE

FERRITE

8X Impedance 8X Impedance

VE2AZX 26

FERRITE IMPEDANCE

- FERRITES VS IRON POWDER … TWO DIFFERENT MATERIALS

- FERRITE: HAS A HIGH PERMEABILITY (10 to 15000)GIVING A HIGH INDUCTANCE FOR A SMALL NUMBER OF TURNS

BUT THE INDUCTANCE OBTAINED IS NOT STABLE AND Q FACTOR IS LOW

OK FOR TRANSFORMERS AND BALUNS

- IRON POWDER: LOWER PERMEABILITY … LOWER INDUCTANCE, GIVES A STABLE, HIGH Q INDUCTANCE (EX.: VFO, FILTERS, TUNERS)

EXAMPLE: AMIDON -> FERRITES and IRON POWDER

PART # - EXAMPLE: FT240-43FT: FERRITE240: External diam in inches X 100 ( here 2.4 in.)43: TYPE OF FERRITE, PERMEABILITY = 850

VE2AZX 27

IMPEDANCE MEASUREMENTS

FREQUENCY RESPONSE MODE

- Does NOT allow measuring separately the Resistive and Inductive components

- Ease of sweeping the frequency

- Reference level = 0 dB = short in place of ferrite

RS

RL

SignalGenerator RF

Voltmeter

Zx

Ferrite UnderTest

SHIELD

RS and RL are generally 50 ohms

To calculate Zx from attenuation readings in + dB’s: Zx = (RL + RS) . (10 - 1)dB20

(assumes that Zx is resistive)

VE2AZX 28

CHECK YOUR FERRITES WITH YOUR SWR ANALYZERFROM SWR MEASUREMENTS

Coax cable shieldAllows for many turns.

Ferrite under test

SWR ANALYZER

Insulating Sleeve

Male UHFConnector

50Ω

Conductor, Cu or Al

The ferrite is in parallel with the 50 ohms (1%) termination

VE2AZX 29

50

500

200

20

IMPÉDANCE APPROX. DU FERRITE VS SWR MESURÉ

10

100

1000

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

SWR

FER

RIT

E I

MPE

DAN

CE

ohm

s

FERRITE IMPEDANCE PURELY INDUCTIVE

FERRITE IMPEDANCE PURELY RESISTIVE

FERRITE IMPEDANCE VS MEASURED SWR

VE2AZX 30

MEASUREMENT OF FERRITE IMPEDANCE

USING AN SWR ANALYZER OR A VECTOR NETWORK ANALYZERAllow measuring separately the Resistive and Inductive Components

Ferrite under test

SWR ANALYZER With IMPEDANCE CAPABILITY

- OR –VECTOR NETWORK

ANALYZER

Insulating Sleeve

Connector

Conductor, Cu or Al

VE2AZX 31

IMPEDANCE MEASUREMENTS

1 turn1 turn – 2 ferrites2 turns

1 MHz 10 MHz 100 MHz 1000 MHz10 Ω

1000 Ω

100 Ω

FREQUENCY MHz

CLAMP ON FERRITE FOR RG-8

YIELDS 80 ohms at 10 MHz for 1 turn

VE2AZX 32

IMPEDANCE MEASUREMENTS

1 10 100 1 1030

1

2

3

4

5

6

FREQUENCE MHz

FAC

TEU

R Q

1 turn

1 turn – 2 ferrites

2 turns

Q F

acto

r

0

6

3

FREQUENCY MHz

10 Ω

1000 Ω

1 MHz 100 MHz10 MHz 1000 MHz

- ABOVE 20 MHz THE Q FACTOR < 1THE IMPEDANCE BECOMES RESISTIVE

VE2AZX 33

IMPEDANCE MEASUREMENTS

1 turn

1 turn – 2 ferrites

2 turns

1 MHz 100 MHz10 MHz 1000 MHz10 Ω

1000 Ω

1 10 100 1 1031

0

1

2

3

4

FREQUENCE MHz

IND

UC

TAN

CE

uH

Indu

ctan

ce u

H

0

4

2- THE INDUCTANCE DECREASES AS

THE FREQUENCY IS INCREASED

- THE INDUCTANCE DISAPPEARSWHEN F > 100 MHz

FREQUENCY MHz

VE2AZX 34

IMPEDANCE MEASUREMENTS

1 turn

2 turns

1 MHz 10 MHz 100 MHz 1000 MHz10 Ω

1000 Ω

100 Ω

FREQUENCY MHz

- THIS IMPEDANCE CURVE IS SIMILAR TO THE PREVIOUS CORE

VE2AZX 35

IMPEDANCE MEASUREMENTS

1 turn

2 turns

1 MHz 10 MHz 100 MHz 1000 MHz10 Ω

1000 Ω

100 Ω

FREQUENCY MHz

- THIS IMPEDANCE CURVE IS SIMILAR TO THE PREVIOUS CORE

VE2AZX 36

IMPEDANCE MEASUREMENTS

4 turns3 turns

2 turns

1 turn

RECTANGULARCLAMP-ON FERRITE

1 MHz 1000 MHz1 Ω

1000 Ω

100 Ω

10 Ω

FREQUENCY MHz10 MHz 100 MHz

- GIVES ~ 10% IMPEDANCE OF PREVIOUS CORES (8 ohms at 10 MHz for 1 turn)

- COVERS MUCH WIDER FREQUENCY RANGE

- SHOULD USE MANY TURNS: 10 TURNS GIVE 800 ohms AT 10 MHz

VE2AZX 37

IMPEDANCE MEASUREMENTS

4 turns3 turns

2 turns

1 turn

1 10 100 1 1035

0

5

10

15

20

FREQUENCE MHz

IND

UC

TAN

CE

uH

2 turns

1 turn

0

10

Indu

ctan

ce u

H

20

FREQUENCY MHz

FREQUENCY MHz

RECTANGULARCLAMP-ON FERRITE

- THE INDUCTANCE DISAPPEARS ABOVE 6 MHz

VE2AZX 38

IMPEDANCE MEASUREMENTS

1 turn

2 turns

4 FERRITES

1 MHz 10 MHz 100 MHz 1000 MHz10 Ω

1000 Ω

100 Ω

FREQUENCY MHz

STACKEDRECTANGULARCLAMP-ON FERRITE

4 TURNS WILL YIELD ~ 800 ohms

VE2AZX 39

TESTING AFERRITEBEAD FERRITE BEAD

APPROX. 0.1 PO. LONG.

ohms

1 MHz 10 MHz 100 MHz 1000 MHz

28 Ω

36 Ω

32 Ω

VE2AZX 40

IMPEDANCE MEASUREMENTS (Done in frequency response mode)

0

30 KHz 100 KHz 1 MHz 10 MHz 30 MHz

78

216

462

900

1678

Impé

danc

e Zx

(Ώ)

4 turns6 toroids

VE2AZX 41

1 MHz 10 MHz 30 MHz

216

900

3162

0

Impe

danc

e (Ώ

)

IMPEDANCE MEASUREMENTS (Done in frequency response mode)

6 toroids 6 turns

VE2AZX 42

IMPEDANCE MEASUREMENTS (Done in frequency response mode)

0.

0

5.9

12.2

18.8

25.9

33.4

Impe

danc

e (Ώ

)2 toroids1 turn

Impedance increasecaused by lead inductance

1 MHz 10 MHz 100 MHz

VE2AZX 43

IMPEDANCE MEASUREMENTS (Done in frequency response mode)

0

78

216

462

900

Impe

danc

e (Ώ

)

2 toroids 5 turns

10 MHz 100 MHz1 MHz

VE2AZX 44

IMPEDANCE MEASUREMENTS (Done in frequency response mode)

Coax with 25, #43 beads

0

78

216

462

900

Impé

danc

e (Ώ

)

10 MHz 100 MHz1 MHz

VE2AZX 45

IMPEDANCE MEASUREMENTS (Done in frequency response mode)

#14 Wire with 50 beads #73

0

78

216

462

900

Impe

danc

e (Ώ

)

Excellent at HF

1 MHz 10 MHz 100 MHz

VE2AZX 46

CURRENT BALUN GIVING A 4:1 IMPEDANCE RATIO

200 Ω

50 Ω

TOROID #1

TOROID #2From: W1CG

- USES 2 PARALLEL WIRES INSTEAD OF A COAX- MAKES A COMPACT TRANSMISSION LINE

NOTE: THIS 4:1 CURRENT BALUNIS SUPERIOR TO THE 4:1 VOLTAGE BALUN

VE2AZX 47

CURRENT BALUN GIVING A 4:1 IMPEDANCE RATIO

BALANCEDSIDE 200 Ω

COAXSIDE 50 Ω

W1CG

Parallel wires make upa transmission line

VE2AZX 48

CURRENT MEASUREMENTS

BALU

N

A

B

C

MEASURE CURRENT AT A, B, C.

CURRENTS AT B AND C SHOULD BE < 10% THE CURRENT AT POINT A

CURRENTPROBE

MFJ-206

YOU CAN MAKE YOUR OWN CURRENT METER

VE2AZX 49

FERRITES MAY BE USED WITH A VOLTAGE BALUN

- WILL FURTHER ISOLATE THE FEEDER FROM THE ANTENNA

- MAY REDUCE THE NOISE PICK-UP BY THE FEEDER

FERRITES

BALU

N

- USE FERRITES AT EVERY QUARTER WAVELENGTH OR AT CURRENT MAXIMA

Current balun

Voltage balun- MESURE THE SHIELD CURRENT

- PUT THE FERRITES AT POINTS OF MAXIMUM CURRENT

- WILL STABILIZE THE ANTENNA IMPEDANCE

VE2AZX 50

CURRENT BALUN MADE UP OF COAX CABLE

BALU

N

- COIL DIAMETER 6 - 12 in. / 5 - 10 TURNS

VE2AZX 51

USING A BALUN ON A VERTICAL ANTENNA

FERRITES

RADIALS

The coax should not bepart of the antenna !

Do not connect to an earthground at this point,If only a few radials are used

Earth ground is OK here

VE2AZX 52

USING FERRITES ON THE FEEDER OF VERTICAL YAGI

PREVENT INTERACTION BETWEEN COAX + MAST WITH YAGI

FIBERGLASS INSULATED MAST

#43 FERRITESLEEVES HELDWITH TAPE ORTIE WRAPS

~ λ/2

Ref: QEX Sept – Oct. 2006

VE2AZX 53

NOTES

- USING A BALUN UNDER HIGH SWR:

VERIFY HEATING OF THE CORE

DECREASE THE POWER

USE MIX 73 (µ=2500) OR 31 (µ=1500) FOR HIGH POWER USE MIX 43 (µ=850) See Ref. 4

BALUN LOSSES MAY / WILL INCREASE UNDER HIGH SWR

VOLTAGE BALUN NOT RECOMMANDED IF SWR > 5:1 UNLESSDESIGNED FOR HIGH SWR

- BALUNS NORMALLY PROVIDE A VERY LOW ATTENUATION, NORMLLY < 0.3 dB … WHEN THE LOAD IS MATCHED

VE2AZX 54

QUARTER WAVE BALUN

- A QUARTER WAVELENGTH (OR ODD MULTIPLES)SHORTED AT THE BOTTOM END WILL GENERATEA HIGH IMPEDANCE AT THE DIPOLE AND MINIMIZECOMMON MODE CURRENTS ON THE COAX OUTER SHIELD.

GROUNDING POINT(Building Entrance Common Plate, Radio ground point, etc.)

λ/4 or oddmultiples

- USE A VELOCITY FACTOR OF 95% IN CALCULATING THE COAX LENGTH

- THIS TECHNIQUE WILL NOT WORK AT FREQUENCIES WHERE THE FEEDER IS A MULTIPLE OF λ/2

Add the length of the grounding wires whencomputing the quarterlambda.

To TX

VE2AZX 55

CANNOT LOCATE BALUN AT DIPOLE FEEDPOINT: TOO HEAVY !

- SETTING THE FERRITES A HALF WAVELENGTH (OR MULTIPLES) FROM THE DIPOLE WILL GENERATEA HIGH IMPEDANCE AT THE DIPOLE AND MINIMIZECOMMON MODE CURRENTS ON THE COAX OUTER SHIELD.

λ/2 ormultiples

- USE A VELOCITY FACTOR OF 95% IN CALCULATING THE COAX LENGTH

GROUNDING POINT(Building Entrance Common Plate, Radio ground point, etc.)

To TXThese lengths are not critical.

FERRITES- THE FERRITE IMPEDANCE SHOULD BE 500Ω

OR MORE. (CHECK FOR HEATING)

- THE LENGTH BETWEEN THE TX AND THE FERRITES IS NON CRITICAL

VE2AZX 56

FERRITES ARE USED EVERYWHERE

Antenna

POWER SUPPLY

XCEIVER

COMPUTER CAMERA

USBCABLE

Ferrite

VE2AZX 57

THINGS TO REMEMBER…

- VOLTAGE BALUNS COVER A VERY WIDE RANGE OF IMPEDANCES

- SET EQUAL VOLTAGES AT THE OUTPUT

- GENERALLY PROVIDE NO PROTECTION AGAINST CURRENTS FLOWINGON COAX EXTERIOR

- MAY BE COMBINED WITH A CURRENT BALUN

- CURRENT BALUNS CREATE A AN IMPEDANCE ON THE OUTSIDE OF THE COAX (OR ANY CONDUCTOR)

- ALSO CALLED COMMON MODE CHOKES

- DECREASE COAX RADIATION AND PICK-UP

- STABILIZE THE ANTENNA IMPEDANCE

- GENERALLY 50:50 ohms RATIO (ALSO 50:200 POSSIBLE)

VE2AZX 58

THINGS TO REMEMBER…

- DECREASE COAX RADIATION ON TRANSMIT

- AND PICK-UP ON RECEIVE

Extract from Ref. 4:

The most common reasons for using common-mode chokes are:

(1) to reduce the fraction of the RF power that is fed to your antenna from your transmitter,but then is conducted back to your shack via common-mode current on yourfeedline, causing RFI trouble in the shack or elsewhere in your house;

(2) to keep the transmitted RF power that 60-Hz power, telephone, TV, and othercables in the field of your antenna pick up, from bothering susceptible devices connectedto these cables in your own and neighbors’ houses

VE2AZX 59

Extract from Ref. 4:

(3) to keep the RF noise that all the electronic devices in your house generate, from being conducted via60-Hz power, telephone and other cables to the outer shield of yourradio, and from there along your feedline(s) to your antenna(s), in common-mode.

W1HIS

VE2AZX 60

REFERENCES

1- General informations on baluns – Index of good articles:http://www.nonstopsystems.com/radio/frank_radio_baluns.htm

2- Transmission Line Transformers, by Jerry Sevick W2FMI

3- Cost effective ferrite chokes and balunshttp://www.nonstopsystems.com/radio/article-cost-effective-chokes.pdf

4- Reducing interferences inside the house: Chuck Counselman W1HIS.http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf

5- FERRITE SUPPLIERSDigikey http://www.digikey.comFair-Rite http://www.fair-rite.comAimdon http://www.amidoncorp.comByteMark http://www.cwsbytemark.com/prices/toroidal.phpThe Toroid King http://www.kitsandparts.com/index.php