HELIX ANTENNASREAL WORLD COMPARISONMEASUREMENTS

Clare - VE3NPC QCWA Dinner Nov. 21, 2006

Early Helix 2 x 10 Turns 1989

2 x 15 Turn 70 cm Helix 1991 ?

AO-13 AntennasAbout 1994

AO-40 Antennas 2001

13 and 23 cm Helix Arrays 2003

So How Did We Do?Only worked AO-40 in mode L/S6 other low orbiters were used by othersUsed Yaesu FT-736R with 10 watts on LThere were 30 submissions We made 102 QSOs, nearly all on SSBPlaced 7th.

VE3NPC L/S QSOs AO-40AO-40 on mode L/S from 16 Sept 01 to 28 Jan 0410 watts output into 4 x 27 T helix array on the L uplinkWorks out to about 1500 watts ERPIn that time I logged 832 QSOs in mode L/S

More Helix Antenna OperationFirst satellite QSO in 1988Now 18 years later have over 11 K Satellite QSOs in logWith 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)

KrausGain (db)=10log3.325nLinear function

Double n (turns) - double gain 3 dbFour 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 KA1GT1995 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 publicationsWeb page helix antenna calculators use NEC peak gain design formulaAMSAT experts come up with peak gain formula dimensions

VE3NPC 1990 or soConstructed several 70cm helix antennas following Bob Atkins design in the ARRL UHF/Microwave Experimenters ManualThey did not give any better performance.Narrower band width and harder to get good feed match

VE3NPC 1992/93Constructed several different 2.4 GHz helix antennas and arrays for AO-13 mode SAll were over 30 turns and most used Bob Atkins peak gain designDidnt work never even heard beaconMade 4 ft dish worked like a charm

Summer 2005Dave VE3KL proposed constructing a 70cm helix antenna using the Emerson designFrom my previous experience I questioned his choice Dave was skeptical.Well that started the ball rollingMaybe I was wrong but I didnt think soSimple matter to compare his with mineWhat appeared to be simple turned into a major projectConstructed and compared 10 different helix antenna

Objectives1 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 & DirectivityAn 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 Design

70 cm 10 Turn Kraus/EmersonKraus 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 turnsEmerson 24 turns

Kraus Design Different Boom Materials

Conclusions

Casts serious doubt on NEC computer modeling of helix antennas

Ant based on modeling doesnt 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 VerificationCan 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 cards40 % did not list type of antOf the 1267 cards listing type of antenna only 37 used a helix (3%)Only 3 were in the USOne VK,FY and FPThe rest European (G3RUH pattern?)22 countries

G3RUH James Miller1993 published design for 16 turn 2401 MHz helixC = 1.06 wavelengthsP.A. 12.5 degrees3.3 mm copper wire conductor Boom 1 x 1 inch aluminumMeasured gain (sun noise) = 15.2 dbicKraus gain = 17.3 dbic

Central States VHF Society Antenna Range Tests 1995-200615 helix antennas for 70cm, 33cm,23cm and 13cm measured

2 met the theoretical (VE3KSK) G3RUH design5 within 1 3 db8 within 4 11 dbWhere theoretical = Kraus gain minus 3 db

Southeastern VHF Society Antenna Range Tests 20062 helix antennas tested at 2304 MHzOne 27 turn and one 16 turn.Both about 1 db less than Kraus gain minus 3 db

AO-40 Orbit 60 k kilometers

Thanks for inviting me to talk to you this eveningI hope it isnt too boring as it is a fairly technical topic that hardly any of you will directly put to use.I have become interested and operated in an area of amateur radio that is rather exclusive to a verysmall number of amateurs. And while the number of satellite operators is small the number that havebuilt their own antennas is even a much smaller number. The next few pictures show a bit of my past satellite antenna building history.2 m quagi and 70 cm helix co-located on the same boomAndy Haydon Park 1989 or 1990I made my first satellite QSO on RS-11 on Nov 18 1988I knew practically nothing about operation on any freq above 30 MHz andAbsolutely nothing about satellite operation2m 2x8 element quagis, 70cm 2x16 turn helix Science Museum 1990 or 19912m 4x6 element quagi, 70cm 4x10 turn helixBy 1993 had settled on using fibre glass stakes for boomsLight weight rugged. These antennas still in use. Only thing done was toreplace a few tie wraps that had deteriorated.The quagi elements are galvenized wire and are getting a bit rusty.Had to straighten a couple of elements where a crow or some large bird tried to sit on them.4x27 turns 23 cm array, 1.2m dish for 2.4 GHz and 2x10 turns 70cm Now 2001

This is 2003 at main street. Added a 13 cm helix array. 4x52 turnsMade 102 QSOs in mode L/S and placed 7th in Satellite operation