Real world comparison measurements clare ve3npc qcwa dinner nov 21 2006
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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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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


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

  • 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

  • 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 !

  • 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

  • Invented by Dr. John D Kraus in 1947

  • He constructed large arrays of helix antennas for radio astronomy


  • “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

  • Gain (db)=10log3.325n

  • Linear function

  • Double n (turns) - double gain – 3 db

  • Four times n – four times gain – 6 db


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

  • C = 1 wavelength

  • pa = 12.5 degrees


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

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.


Bob Atkins


Emerson


Cebik


Cebik


Emerson - Length


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

  • 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

  • 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

  • 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

  • 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.


Test Equipment Set Up


Antenna Test Range


Comparison Results Between Four Kraus Design Helix Antennas of Increasing length. C = 1 w/l P.A.= 12.5 deg.


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

12 turns

6.5 turns

26 turns

52 turns


Increasing Turns/Gain Differences


Comparison Results Between Kraus Design and Emerson Design


70 cm 10 Turn Kraus/Emerson

Kraus 10 turns

Emerson 10 turns


12.5 cm 2.88 w/l Kraus/Emerson

Emerson 12 turns

Kraus 13 turns


12.5 cm 5.75 w/l Kraus/Emerson

Kraus 26 turns

Emerson 24 turns


Kraus Design – Different Boom Materials


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

  • Can find no other information on direct experimental evidence to verify the computer modeling results of helical antennas !


Questions ? ? ?


VE3NPC 23cm Array Constructed by KB9UPS

VE3NPC

KB9UPS


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

  • 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

  • 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

  • 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

60 k kilometers


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