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