Small 500 KHz Transmitting AntennasVE3KL

04/18/23 David Conn VE3KL 1

Vertical 500 KHz Antenna….. Courtesy (Gunnar SM6BGP)Height = 30 metres

R (antenna) = 22 Ohms ….. measured

Top Hat

InsulatedBase

Many Possible Antenna Types

04/18/23 David Conn VE3KL

N Monopoles Separately FedClosely SpacedSTAR-H Patent

Gunnar….SM6BGP

Presentation Outline • Basics..Radiation Resistance, Efficiency,

Bandwidth• Vertical Antennas • Inverted L Antenna…..briefly• Loop Antennas• Other types including the Horizontal Dipole• Bibliography

04/18/23 David Conn VE3KL 3

Acknowledgements

• OARC, RAC, Bryan (VE3QN), Oliver Conn • Industry Canada..Justine Sider (computer use)• Gunnar….SM6BGP….Permission to use material

from Web site• RIK..ON7YD……permission to use diagrams from

Web site• STAR-H Corp….a patented novel short AM monopole

with high radiation resistance.. the author wishes to thank STAR-H for permission to experiment with this antenna (non-commercial use)

04/18/23 David Conn VE3KL 4

The Problem

• Selecting and Designing reasonably sized transmitting antennas for 600 metre wavelength amateur radio applications.

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Design Methodology

• Analytic design using basic equationsVery broad in concept…not specific

• Simulation using method of moments (NEC-4)Specific to an exact configurationMust be careful…many limitations and approximations. Used by VE3KL to evaluate all Canadian license applications

• Build, Measure and TestThe ultimate, but few test ranges available for 500 KHz antennas

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Design Issues(Small Antennas)

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Radiation/Ground Resistance

Efficiency

Bandwidth

Design Issues(Small Antennas)

• Low Radiation Resistance

• Low Efficiency

• Narrow Bandwidth….small capacitance

• Space Limitations…….600 metre λ

• Simulation Problems….NEC4 needed

for buried radials

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Radiation Resistance, RrDefinition

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Prad = Io2Rr/2 [Watts]

Prad = Power radiated from an antenna

I = IoCos(2πft)

Rr for a half wave dipole = 73 Ohms

Antenna Efficiency

04/18/23

David Conn VE3KL

10

]RlossRr/[RrEfficiency

Efficiency = Rr/Rloss (for small Rr)

Doubling Rr doubles the antenna efficiency

Rr = Radiation ResistanceRLoss = copper loss plus ground loss

Antenna Efficiency

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]RlossRr/[RrEfficiency

Rr = radiation resistance…….Rloss = loss resistance

Example: Rrad = 0.5 Ohms, Rloss = 22 Ohms

Efficiency = 0.5/22.5 = 0.022 = 2.2% (-17dB)

Antenna Bandwidth

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•Several ways to define Bandwidth: 3 dB, SWR, Return Loss

•Calculated from Antenna Equivalent Circuit

•Can be very small ( 1 KHz ) for small antennas

Frequency

ExampleB = 4 KHz for SWR = 2:1

SWR

B

1.0

2.0

Vertical Antennas

• Basics…applies to all antennas

• Vertical Antenna No Top Hat, Top Hat

• Case study of a vertical monopole with top hat…SM6BGP

• Vertical STAR-H Type Antenna

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Current

Short Vertical Monopoles with and without a Top Hat.Top Hat forces current to be nearly uniform along antenna. Radiation resistance increased with a Top Hat.

Current

Ground

Top Hat

L L

Short Vertical MonopolesBase Fed

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D

Top View

Side View

Ground

Monopole

Voltage Source

Monopoles Receive Equal Power

L

Star-H Vertical CageConcept Similar to Folded Dipole

Closely SpacedTightly Coupled

Big Increase in Rr, B and Efficiency

Radiation ResistanceBasic Vertical Elements

• Small Current Element….basic element

• Short Vertical Monopole…no top hat

• Short Vertical Monopole…ideal top hat

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Radiation Resistance (Rr)Basics…..Small Current Element

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IoCOS(2πfot)

L metres long

Power Radiated = Io2Rr/2 [Watts]

2280

L

Rr

Radiation Resistance (Rr)Small Current Element..Example

L/λ = 0.05 Io = 5.0 Amps

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IoCOS(2πfot)

30 metres long

PowerRadiated = Io2Rr/2 = 25 [Watts]

2280

L

Rr Rr = 2 [Ohms]

Short Vertical MonopoleA Simple Basic Antenna L/λ = 0.05

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Current varies linearly on antenna

Approximately 16 Ground Radials

2240

L

Rr Rr = 1.0 Ohm

H=LL= 30 metres @500 KHz

Short Vertical MonopoleEfficiency

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ON7YD DiagramShort Vertical Monopole

Current varies linearly on antenna

Length = 30 metres Frequency = 500 KHz

Rrad = 1.0 Ohm, Rloss = 21 Ohms (Typical Measured)

Efficiency = 1.0/22 = 0.045 = 4.5% (-13 dB)

L = H

2240

L

Rr

Short Vertical Monopole Capacitance

L=30 m

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H = L

L = length [m] d = wire diameter [m]Cv in pF

Example fo = 500 KHz, L = 30 m, d = 0.001m: Cv = 158 pF Xo = 1/(2πfoCv) = 2015 Ohms

Rg must be measured

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Rr +RlossCvTuning CoilTransMatchSWR

Antenna

Bandwidth: Frequency range between specified SWR level

Antenna BandwidthVertical Antennas

(Radio Definition…SWR based)

SWR

B

1.0

2.0

SWR =1.0 @ fo

fo

Antenna BandwidthVertical Antennas

(Radio Definition…SWR based)

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• B is the Bandwidth [Hz]• R is the input resistance of the antenna [Ohms]• Xo is the input reactance of the antenna [Ohms]• fo is the operating frequency [Hz]• SWR is the maximum permissible SWR

Example: SWR = 2:1, R = 22, Xo = 2015, fo = 500 KHz

B = 3.8 KHz……. Very low….poor for high speed data communications

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Antenna Bandwidth [KHz]

0

10

20

30

40

50

60

70

80

90

100

0 0.05 0.1 0.15 0.2

R/Xo

Ban

dw

idth

[K

Hz]

SWR=1.1 SWR=1.5 SWR=2.0 SWR=2.5

Example:Vertical Antenna No Top HatHeight = 0.05 wavelengths

SWR = 2.0Rantenna = 22 ΩXo = 2015 Ω

BW = 3.8 KHz

Bandwidth.. Vertical No Top Hat

Our Range

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Bandwidth.. Vertical No Top Hat

• Narrow Bandwidth creates Temperature and Drifting problems

• Narrow Bandwidth sets limits on the Transmission Data Rate

• Lowering loss resistance lowers the Bandwidth

• Bandwidth dominated by loss resistance

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Summary Vertical No Top Hat

fo = 500 KHzL = 30 metresMax. SWR = 2:1Rr = 1.0 Ohms, Cv = 158 pFRloss = 21 Ohms……based on measurements of SM6BGP

Efficiency = 1/22 = 0.045 = 4.5% (-13 dB)BW = 3.8 KHz

Short Vertical Monopole with Top Hat

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Analysis for one Top Hat Element Approximate analysis..only vertical Ra consideredGenerally many Hats are used

Short Vertical Monopole with ideal Top HatRadiation Resistance

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Rr = 4.00 Ohms for 30 metre high antenna with ideal top hat

H

2

2

22

H

H2 CearglforH

160H

CvC

CvC240Ra

Four times that of the VerticalWith no top hat

Short Vertical Monopole with ideal Top HatSummary

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Increased Radiation ResistanceIncreased CapacitanceSame Ground Loss

Hence increased efficiencyIncreased Bandwidth

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Radiation Resistance [Ohms]

0

1

2

3

4

5

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

Length [Wavelengths]

Ra

dia

tio

n R

es

ista

nc

e

[Oh

ms

]

Short Dipole Vertical No Top Hat

Current Element Vertical Top Hat

Summary..Radiation Resistance of Basic Elements

Note the Vertical Scale

4 Ohms

1 Ohm

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Good Time for a Break

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D

Top View

Side View

Ground

Monopole

Voltage Source

Monopoles Receive Equal Power

L

Star-H Vertical CageConcept Similar to Folded Dipole

Closely SpacedTightly Coupled

Big Increase in Rr, B and efficiency

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Star-H Vertical CageBased on Closely Coupled Line Analysis

(Ramo-Whinnery-VanDuzer)

1 2

1 Amp 1 Amp

Zin = Z11 +Z12Z12 ≈ Z11 for close coupling

Zin = 2 Z11

Input impedance doubled

Radiation Resistance Star-H CageNo Top Hat

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2240

LNRr

Increases with N

Radiation Resistance Star-H CageWith Ideal Top Hat

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Increases with N

22160

LNRr

Four times

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Example:N = 8L = 0.05Rr = 7 Ohms

Rr (Cage No Top Hat)[Ohms]

0

5

10

15

20

25

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

Length [Wavelengths]

Rad

iatio

n R

esis

tan

ce [O

hm

s]

N=2 N=4

N=8 N=10

Radiation Resistance Star-H Cage

Note the Scale

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Example:N = 8L = 0.05Rr > 25 Ohms

Very Easy to Match

Rr (Cage Top Hat) [Ohms]

0

5

10

15

20

25

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

Length [Wavelengths]

Ra

dia

tio

n R

es

ista

nc

e [

Oh

ms

]

N=2 N=4

N=8 N=10

Radiation Resistance Star-H Cage

Note theScale

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Other AntennasHorizontal Dipole

• Radiation Resistance of ideal horizontal dipoleover perfect ground gets very small..the ground shorts out the electric filed

• Ra ≤ 2.0 Ohms for a λ/2 dipole 15 metres high @ 500 KHz

• High ground/copper loss produces very low efficiency

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Example:Perimeter = p = 120 mλ = 600 m

RA = 0.07 Ohms

Small Loop AntennaDual of the Short Dipole

uA

RA 4

24320

Small

L

L

A2 = L 4

Rloss = 4ρL Ohms

Source

Wires

04/18/23 David Conn VE3KL

Inverted L Antenna

•An extension of the top hat vertical•Both lines radiate•Not easily analyzed ?•Very commonly used with good results•Amenable to simulation with NEC-4•Needs extensive radial system under the top portion

Ground

L2

L1

Source

L1 + L2 = λ/4

Ra = 6 Ohms for L1 = 0.05λ

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Bibliography

• ON4UN, Low-Band Dxing…..ARRL, get latest version • Fields and Waves in Communication Systems, Ramo, Whinnery,

Van Duzer, Third edition, John Wiley• Star-H corporation• ON7YD, SM6BGP, LX/PA6Z, SK6RUD web sites• Cebik web site• Presentation posted on ve3kl.com web site• VE3XK, Ground-Mounted Verticals: West Carleton Amateur Radio Club

web site

04/18/23 David Conn VE3KL 42

Summary

• Presented guidelines for selecting and designing 600 metre transmitting antennas

• Showed the relationship between Radiation Resistance, Bandwidth and Efficiency

73 Dave VE3KL