HELIX ANTENNAS REAL WORLD COMPARISON MEASUREMENTS Clare - VE3NPC QCWA 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 7 th.

VE3NPC L/S QSO’s AO-40 AO-40 on mode L/S from 16 Sept 01 to 28 Jan 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 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

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. Number of Turns Length in Wave- lengths Theor. Gain db Incremental Theor. Gain db Incremental Measured Gain db Theor. B/W deg. Measured B/W deg. 6 1/

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 Design TypeNo of Turns Length in Wave- lengths Theor. Gain db Measured Relative Gain db Theor. Beam Width deg Measured Beam Width deg K 70cm E 70cm K 12.5cm E 12.5cm K 12.5cm E 12.5cm

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 Materials Boom Material No of Turns Length in Wave- lengths Theor. Gain db Relative Measured Gain db Theor. Beam Width deg Measured Beam Width deg Fiber- glass PVC Pipe Aluminum

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 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 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 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