Helix Antennas

HELIX ANTENNASHELIX ANTENNAS

REAL WORLD COMPARISONREAL WORLD COMPARISONMEASUREMENTSMEASUREMENTS

Clare - VE3NPCClare - VE3NPC

QCWA Dinner Nov. 21, 2006QCWA Dinner Nov. 21, 2006

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.

Numberof Turns

Length inWave-lengths

Theor.Gain db

Incremental Theor.Gain db

Incremental Measured Gain db

Theor. B/W deg.

Measured B/W deg.

6 1/2 1.44 13.4 0 0 43.3 46

13 2.88 16.4 + 3.0 + 2.9 30.6 32

26 5.76 19.4 + 6.0 + 6.2 21.7 20

52 11.53 22.4 + 9.0 + 7.5 15.3 12

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

6.5 turns 12 turns

26 turns 52 turns

Increasing Turns/Gain Differences

Comparison Results Between Kraus Design and Emerson DesignType No of

TurnsLength inWave-lengths

Theor.Gain db

MeasuredRelative Gain db

Theor.Beam Width deg

MeasuredBeamWidth deg

K 70cm 10 2.22 15.2 0 34.7 40

E 70cm 10 2.40 12.8 +1 29 36

K 12.5cm 13 2.88 16.4 0 30.6 32

E 12.5cm 12 2.88 13.2 +0.4 27 25

K 12.5cm 26 5.76 19.4 0 21.7 20

E 12.5cm 24 5.76 14.9 -6.1 20 44

70 cm 10 Turn Kraus/Emerson

Kraus 10 turns Emerson 10 turns

12.5 cm 2.88 w/l Kraus/Emerson

Kraus 13 turns Emerson 12 turns

12.5 cm 5.75 w/l Kraus/Emerson

Kraus 26 turns Emerson 24 turns

Kraus Design – Different Boom MaterialsBoom Material

No ofTurns

Length in Wave-lengths

Theor.Gain db

Relative MeasuredGain db

Theor.BeamWidth deg

MeasuredBeamWidth deg

Fiber-glass

13 2.88 18.1 0 30.8 32

PVCPipe

13 2.88 18.1 +0.3 30.8 30

Aluminum 13 2.88 18.1 0 30.8 32

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

KB9UPS VE3NPC

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