real world comparison measurements clare ve3npc qcwa dinner nov 21 2006
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HELIX ANTENNAS

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REAL WORLD COMPARISON MEASUREMENTS Clare - VE3NPC QCWA Dinner Nov. 21, 2006. HELIX ANTENNAS. Early Helix – 2 x 10 Turns. 1989. 2 x 15 Turn 70 cm Helix . 1991 ?. AO-13 Antennas. About 1994. AO-40 Antennas. 2001. 13 and 23 cm Helix Arrays. 2003 .

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real world comparison measurements clare ve3npc qcwa dinner nov 21 2006
REAL WORLD COMPARISON

MEASUREMENTS

Clare - VE3NPC

QCWA Dinner Nov. 21, 2006

HELIX ANTENNAS
ao 13 antennas
AO-13 Antennas

About 1994

so how did we do
So How Did We Do?
  • Only worked AO-40 in mode L/S
  • 6 other low orbiters were used by others
  • Used Yaesu FT-736R with 10 watts on L
  • There were 30 submissions
  • We made 102 QSO’s, nearly all on SSB
  • Placed 7th.
ve3npc l s qso s ao 40
VE3NPC L/S QSO’s AO-40
  • AO-40 on mode L/S from 16 Sept 01 to 28 Jan 04
  • 10 watts output into 4 x 27 T helix array on the L uplink
  • Works out to about 1500 watts ERP
  • In that time I logged 832 QSO’s in mode L/S
more helix antenna operation
More Helix Antenna Operation
  • First satellite QSO in 1988
  • Now 18 years later have over 11 K Satellite QSO’s in log
  • With exception of mode A and K used in early RS satellites all were made using home brew helix ants for 70cm up and down links and 23 cm uplinks
so what
So What !
  • I have learned a lot about building and operating helix antennas.
  • They have worked very well on the air in competition with commercial crossed yagis, loop yagis and dishes that most satellite operators were and are using.
  • What my paper is about is that according to some published antenna modeling theory they should not have worked as well as the have.
the helix antenna
THE HELIX ANTENNA
  • Invented by Dr. John D Kraus in 1947
  • He constructed large arrays of helix antennas for radio astronomy
slide12
“the dimensions of the helix are so non-critical that the helical beam antenna is one of the simplest types of antenna it is possible to make”
  • circumference
  • turn spacing (phase angle)
  • reflector size
  • conductor diameter
  • helix support (boom)
kraus
Kraus
  • Gain (db)=10log3.325n
  • Linear function
  • Double n (turns) - double gain – 3 db
  • Four times n – four times gain – 6 db
kraus1
Kraus
  • Satellite Experimenters Handbook

0.8 > C > 1.2 C = circumference in wavelengths

12 < a > 14 a = pitch angle in degrees

But used C = 1 wavelength and a =12.5 degrees

v e3npc
V E3NPC
  • C = 1 wavelength
  • pa = 12.5 degrees
helix antenna computer modeling nec
Helix Antenna Computer Modeling (NEC)
  • 1990 ARRL UHF/Microwave Experiments Manual – Bob Atkins KA1GT
  • 1995 ARRL Antenna Compendium - Emerson
  • 2005 Proceedings of the Southeastern VHF Society – Cebik W4RNL
nec design theory
NEC Design Theory

The NEC designs concluded that :

- for a given number of turns there was a

particular value of circumference and

pitch angle that would provide peak gain.

- as the number of turns was increased the

increase in gain soon leveled off.

consequences
Consequences
  • NEC modeling peak gain designs used in ARRL publications
  • Web page helix antenna calculators use NEC peak gain design formula
  • AMSAT “experts” come up with peak gain formula dimensions
ve3npc 1990 or so
VE3NPC 1990 or so
  • Constructed several 70cm helix antennas following Bob Atkins design in the ARRL UHF/Microwave Experimenters Manual
  • They did not give any better performance.
  • Narrower band width and harder to get good feed match
ve3npc 1992 93
VE3NPC – 1992/93
  • Constructed several different 2.4 GHz helix antennas and arrays for AO-13

mode S

  • All were over 30 turns and most used Bob Atkins peak gain design
  • Didn’t work – never even heard beacon
  • Made 4 ft dish – worked like a charm
summer 2005
Summer 2005
  • Dave VE3KL proposed constructing a 70cm helix antenna using the Emerson design
  • From my previous experience I questioned his choice
  • Dave was skeptical.
  • Well that started the ball rolling
  • Maybe I was wrong but I didn’t think so
  • Simple matter to compare his with mine
  • What appeared to be simple turned into a major project
  • Constructed and compared 10 different helix antenna
objectives
Objectives
  • 1 To compare the peak gain design verses the simple Kraus design.
  • 2 To test the validity of the difference in gain relative to the number of turns (length in wavelengths).
  • 3 To test the effects of different boom materials.
slide30
Comparison Results Between Four Kraus Design Helix Antennas of Increasing length. C = 1 w/l P.A.= 12.5 deg.
gain directivity
Gain & Directivity
  • An antenna may be very directive i.e. exhibit a narrow forward beam width but due to the configuration of the side lobes and/or degree of losses, provide higher or lower forward gain
kraus 12 5 cm increased turns
Kraus 12.5 cm-Increased Turns

12 turns

6.5 turns

26 turns

52 turns

70 cm 10 turn kraus emerson
70 cm 10 Turn Kraus/Emerson

Kraus 10 turns

Emerson 10 turns

12 5 cm 2 88 w l kraus emerson
12.5 cm 2.88 w/l Kraus/Emerson

Emerson 12 turns

Kraus 13 turns

12 5 cm 5 75 w l kraus emerson
12.5 cm 5.75 w/l Kraus/Emerson

Kraus 26 turns

Emerson 24 turns

conclusions
Conclusions
  • Casts serious doubt on NEC computer modeling of helix antennas
  • Ant based on modeling doesn’t give predicted peak gain
  • 30 Turn helix ants can be made that will give real gain. Useful gain with 52 turns.
  • Aluminum or PVC OK for boom
other verification
Other Verification
  • Can find no other information on direct experimental evidence to verify the computer modeling results of helical antennas !
who cares
WHO CARES !!
  • Checked my satellite QSL cards
  • 40 % did not list type of ant
  • Of the 1267 cards listing type of antenna only 37 used a helix (3%)
  • Only 3 were in the US
  • One VK,FY and FP
  • The rest European (G3RUH pattern?)
  • 22 countries
g3ruh james miller
G3RUH – James Miller
  • 1993 published design for 16 turn 2401 MHz helix
  • C = 1.06 wavelengths
  • P.A. 12.5 degrees
  • 3.3 mm copper wire conductor
  • Boom 1 x 1 inch aluminum
  • Measured gain (sun noise) = 15.2 dbic
  • Kraus gain = 17.3 dbic
central states vhf society antenna range tests 1995 2006
Central States VHF Society Antenna Range Tests 1995-2006
  • 15 helix antennas for 70cm, 33cm,23cm and 13cm measured
  • 2 met the theoretical (VE3KSK) – G3RUH design
  • 5 within 1 – 3 db
  • 8 within 4 – 11 db
  • Where theoretical = Kraus gain minus 3 db
southeastern vhf society antenna range tests 2006
Southeastern VHF Society Antenna Range Tests 2006
  • 2 helix antennas tested at 2304 MHz
  • One 27 turn and one 16 turn.
  • Both about 1 db less than Kraus gain minus 3 db
ao 40 orbit
AO-40 Orbit

60 k kilometers

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