with an antenna that is

Report
Joe Horanzy AA3JH
April 4th, 2013 K3DN Presentation
Agenda
• Awards
• Impedance
• Measuring Equipment
• Picking the Antenna
• Antenna components with construction tips and theory
• Putting it all together
• Multiband
• Getting more gain
• Simulation tools
• Vertical Moxon
• Future plans
Awards
10 meter progress
Open to all license classes
Impedance
Z = R + jX
Where R = natural antenna and grd loss resistance
X = total antenna reactance combination
of capacitance and inductance
Reactance (X) is your enemy. Why?
A reactive component alternately absorbs energy from the
circuit and then returns energy to the circuit. A pure
reactance will not dissipate any power.
Impedance
You can’t go by just impedance (Z) alone.
A Z of 50 of resistance vs. a Z of 50 reactance is very different.
A Z of 50 of pure resistance = SWR 1:1
A Z of 50 of reactance = SWR >20:1 !
A Z of 100 of pure resistance = SWR 2:1
A Z of 100 of reactance = SWR >20:1 !
Impedance
“So I have residual reactance, so what? I’ll tune it out with my
trusty antenna tuner in the shack.”
#1
Remove all reactance at the antenna.
Matching at the transceiver only satisfies the
connection between the transceiver and the tuner.
Loss in the cable dramatically increases
Impedance
Measuring Equipment
Picking the antenna
Main Object: Get on HF to communicate around the
world (DX) with an antenna that is:







Simple
Low maintenance
Ease of construction
Readily available components
Stealth
Low cost
But very efficient and effective.
The Vertical Antenna
•
Few components, low cost.
•
Easy to hide.
•
Easy to make multiband.
•
Has low take off angle, great for DX
•
DX is not line of sight. Polarization doesn’t matter.
•
Vertical dipoles: don’t need ground radials but is ½ l and
end fed requires matching.
•
¼ wave vertical: only ¼ l high (half the V/D height), no
balun required, but requires ground radials.
The ¼ Wave Vertical
They get a bad name because many don’t radiate from
improper installation from:
 Ineffective ground plane / counterpoise
 Residual reactance, not resonating.
 Improper trap design causing excess loss.
Anytime you move from the basic antenna, there will always
be compromises either through power loss and/or bandwidth
limitations.
The ¼ Wave Vertical
The ¼ Wave Vertical
Single Band
1. How high:
*235/ Freq (Mhz)
example: for 14.1 Mhz 20 meter band
235 / 14.1 = 16.7 feet.
*235 is from: 300 M meter/sec (speed of light) X 95% (speed of light slows down
in wire) /4 (1/4 wave) X 3.3 ft/m (convert to ft)
The ¼ Wave Vertical
Ground system
2. How many ground radials
why?
 Soil has high resistance.
 To reduce ground resistance
as much as possible.
 Any power that is dissipated
in the soil weakens the signal.
As they say: heating up the worms
From Arrl Antenna handbook
Ground loss
Rr: Antenna’s natural radiations resistance: is the virtual resistance
in transferring the energy to produce the radio wave.
For ¼ wave vertical antennas, it’s about 36 ohms. (note: SWR 1:4)
Rg: Ground loss resistance.
Rtotal = Rr + Rg
 Z = Rtotal + jX
Antenna efficiency (%) = (Rr / Rtotal ) x 100
xmit
Rr: Radiated
resistance
Rg: Ground
resistance
For example: say ground resistance is 14 ohm, then
Rtotal = 36 + 14 = 50 ohms, great SWR but…
Efficiency = 36/50 x 100 = 72 percent
From Arrl Antenna handbook
If 100 W is transmitted only 72 watts is being radiated.
Ground radials
The ¼ Wave Vertical
2. Ground radials length:
.25 l or greater. For multiband, use random lengths.
3. Wire size:
12 or 14 AWG
4: Type:
Stranded for vertical
Solid for ground radials
5: Insulated: Doesn’t matter.
COMPONENTS
OR
Putting it all together
Bungee
cord
20M trap
Ground
Connection
Ground
Connection
Close up
Multiband Vertical
Resonate Traps:
Trap:
Inductor/
HV Cap
Multiband Vertical
Another approach
Fan Vertical
Contacts made with home brew
fan vertical antenna (40 to 10 meter)
No amplifier.
Summary
• Cancel out all reactance at the antenna.
• Install best ground radials as possible to keep
ground resistance low as possible.
• Keep all component loss in the system to a
minimal.
• Use good coax, RG213 or better, and ensure all
connections are soldered correctly (beware of
HRO).
Gain
Dbi : Gain measured in relation to an isotropic radiator, an imaginary
antenna in freespace.
Dbd : is a reference to a dipole antenna in free space and is simply Dbi - 2.15
Dipole in freespace can have 2.15 Dbi gain or 0 Dbd.
From Arrl Antenna handbook
Vertical ¼ wave
vs. Horizontal
Dipole
Vertical
Horizontal
Azimuth Pattern:
Antenna radiation
pattern viewed from
above.
Vertical ¼ wave
vs. Horizontal
Dipole
Horizontal
Vertical
Elevation Pattern: Angle
of maximum radiation in
relation to the ground.
Lower the better for DX.
Height above ground of a Horizontal
antenna to be effective
“Sky shooter”
Bad for DX
Comparable to vertical
More gain than vertical
Would require rotator
Lowers angle even more
Creates multiple lobes
How to get gain out of my vertical?
Yagi style but vertical?
The Moxon
Variation of the Yagi
Compact than Yagi
Equivalent gain of a Yagi
High front back ratio
The Moxon
http://www.moxonantennaproject.com/design.htm
Free simulation software
http://www.qsl.net/4nec2/
Free simulation software
Vertical Moxon
Simulated results
Horizontal Moxon
Simulated results
The Vertical Moxon
End Fed Matching Network
• Pick permeability
•
too low: too much wire
•
too high: more loss
• Self resonate secondary winding
in band to prevent additional
reactance (16T)
• Measure Z at antenna input (2K)
• Calculate turns ratio:
•
Calculate primary winding:
16/6.3 = 2.5 turns
• Short secondary, measure
primary Z, note reactance.
• To cancel out the inductive
reactance, put series capacitor
with same reactance in series
with the input of the primary.
The Vertical Moxon
Future plans
Hex Beam
Future plans
Hex Beam
Future plans
Hex Beam
Thank you very much
DE AA3JH

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