small 500 khz transmitting antennas ve3kl 5/5/2015david conn ve3kl1 vertical 500 khz antenna….....
TRANSCRIPT
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.
04/18/23 David Conn VE3KL 5
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
04/18/23 David Conn VE3KL 6
Design Issues(Small Antennas)
04/18/23 David Conn VE3KL 7
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
04/18/23 David Conn VE3KL 8
Radiation Resistance, RrDefinition
04/18/23 David Conn VE3KL 9
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
04/18/23 David Conn VE3KL 11
]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
04/18/23 David Conn VE3KL 12
•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
04/18/23 David Conn VE3KL 13
04/18/23 David Conn VE3KL 14
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
04/18/23 David Conn VE3KL 15
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
04/18/23 David Conn VE3KL 16
Radiation Resistance (Rr)Basics…..Small Current Element
04/18/23 David Conn VE3KL 17
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
04/18/23 David Conn VE3KL 18
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
04/18/23 David Conn VE3KL 19
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
04/18/23 David Conn VE3KL 20
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
04/18/23 David Conn VE3KL 21
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
04/18/23 David Conn VE3KL 22
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)
04/18/23 David Conn VE3KL 23
• 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
04/18/23 David Conn VE3KL 24
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
04/18/23 David Conn VE3KL 25
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
04/18/23 David Conn VE3KL 26
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
04/18/23 David Conn VE3KL 27
Analysis for one Top Hat Element Approximate analysis..only vertical Ra consideredGenerally many Hats are used
Short Vertical Monopole with ideal Top HatRadiation Resistance
04/18/23 David Conn VE3KL 28
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
04/18/23 David Conn VE3KL 29
Increased Radiation ResistanceIncreased CapacitanceSame Ground Loss
Hence increased efficiencyIncreased Bandwidth
04/18/23 David Conn VE3KL 30
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
04/18/23 David Conn VE3KL 31
Good Time for a Break
04/18/23 David Conn VE3KL 32
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
04/18/23 David Conn VE3KL 33
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
04/18/23 David Conn VE3KL 34
2240
LNRr
Increases with N
Radiation Resistance Star-H CageWith Ideal Top Hat
04/18/23 David Conn VE3KL 35
Increases with N
22160
LNRr
Four times
04/18/23 David Conn VE3KL 36
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
04/18/23 David Conn VE3KL 37
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
04/18/23 David Conn VE3KL 38
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
04/18/23 David Conn VE3KL 39
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
04/18/23 David Conn VE3KL 41
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