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## PowerPoint Slideshow about 'HELIX ANTENNAS' - Lucy

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2 x 15 Turn 70 cm Helix

1991 ?

AO-13 Antennas

About 1994

AO-40 Antennas

2001

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.

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.

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

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 !

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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