Presentation on theme: "A Study of Stacked Arrays of Yagi-Uda Antennas Jay Terleski, WX0B 1."— Presentation transcript:
A Study of Stacked Arrays of Yagi-Uda Antennas Jay Terleski, WX0B 1
15m Example 120/90/65 2 WX0Bs 10 and 15 m stacks
15m Example 3 A good model which applies to 20 and 10 meters will be a 4 element 23 foot design. Most antenna manufactures offer a similar antenna to this design. 40 meters we will will use 2 and 3 element beams common to Hams.
Why do we stack yagis Gain Clean up pattern Control of Take-off angle Beam in multiple directions Suppress rain, snow, wind static 4
Gain 5 Single 15m yagi at 125 feet 14.71 dbi gain @ 5
Gain 6 125/95 stack with 17.01 dbi gain @ 6 degrees
Gain 7 120/90 stack with 17.01 dbi gain @ 6 degrees125/95/65 stack 18.34 dbi gain @ 6 degrees
Gain 8 125/95/65/35 stack 18.54 dbi gain @ 7 degrees
Why do we stack yagis Gain Control of Take-off angle 9
Boom length and spacing 29 14.97 dBi gain @ 8 degrees - bad lobe goin UP! 30 ft space
Boom length and spacing 30 Great pattern - gain 15.28 dBi @ 8 degrees 25 ft space
Boom length and spacing Short booms vs. spacing C3 stack or any short Yagi. 31 Just right 15.46 dBi @ 8 degrees 27 ft space
Boom length and spacing 32 How to calculate the best spacing based on boom length?
Boom length and spacing 1.0 WL booms = 1 WL spacing.75 WL booms =.87 WL spacing.5 WL booms =.707 WL spacing.25 WL booms =.5 WL spacing Short booms are very critical, model it to be certain. 33 S (WL) = ( Boom Length in WL)
What about stacking Dissimilar antennas? Matching technique - are they the same? Driven element offsets must be know. Baluns are they the same? 34
Dissimilar antenna stacks It can be done with certain precautions Example 3 ele with 4 ele 15 m. Same match, same balun 34 3 foot offset
Dissimilar antenna stacks 35 Slurred pattern less gain 15.7 dbi @ 6 degrees
Dissimilar antenna stacks 36 3 feet / 44.4 ft (WL) X 360 degrees = 24.3 degrees of delay is required to put these antennas in phase. 3 feet X.66 (VF of RG213) = 1.98 feet of coax would need to be added to the leading driven element. Lets correct the model by adding in the delay line and see the resulting pattern
Dissimilar antenna stacks 37 Well defined nulls, more gain, 17.03 dBi @ 6 degrees a gain of 1.33 dBi
Dissimilar antenna stacks 37 Well defined nulls, more gain, 17.03 dBi @ 6 degrees a gain of 1.33 dBi Slurred pattern less gain 15.7 dbi @ 6 degrees
Dissimilar antenna stacks 37 What if Beams, Matching and Baluns are not the same? 3 foot offset Gamma matched balun X Hairpin matched & balun Y
Dissimilar antenna stacks 37 O-Scope, equal feed lines, and a friend are needed.
Dissimilar antenna stacks 37 Measure the angle of delay needed to align pattern Build a coax delay line and add to the leading antenna’s feed line.
Horizontal Stacking 52 16.5 dBi @ 5 degrees with a delay of 298 deg. Drive impedance varies as delays are changed
Issues With Stagger Types That Turn 53 Close coupling is a problem Drive impedance vary widely as the array turns Matching will be a problem - very difficult to adjust This type of array is probably not suitable unless everything remains fixed as in an H-Frame or parallel tower single direction arrays More work needs to be done on LAPA type arrays for amateur work
What Happens When I Beam in Multiple Directions? 54 Will rotating a Yagi 180 degrees in a stack cancel the forward pattern intended? Or will it allow the forward pattern to survive? Will rotating a Yagi in a stack achieve the intended pattern? That is, to beam in two directions at once? Or will it mess up the pattern?
Multi-direction Beaming 55 Rotate this beam 90 and 180 degrees
Multi-direction Beaming 56 Same direction - 3 high 6 degrees AZ pattern - 18.46 dBi gain
Multi-direction Beaming 58 Middle rotated 90 degrees - 14.86 a loss of 3.6 dBi this is fine
Multi-direction Beaming 59 Rotate 180 degrees - 15.84 dBi forward loss of 2.62 dBi forward F/B is now only 8.2 dB - This is effective and expected
Multi-direction Beaming 60 Will rotating a Yagi in a stack achieve the intended pattern? That is, to beam in two directions at once? Yes, all beams in a properly spaced stack may be rotated individually without regard to cancellation. Will rotating a Yagi 180 degrees achieve the intended pattern? Yes, all three are fine to rotate.
Summary - GAIN VERTICAL STACKS must be properly spaced Gain of 2.2-3 dB from adding second antenna Gain of 1.5-2 dB by adding a third antenna Gain of.5 - 1 dB by adding a fourth antenna 61
Summary -Take off Angle Switching allows control of take off angle including BOP Angle of lobes can be bad due to poor spacing of yagis Stack lobe will always slightly higher than top yagi alone 18-20+ dB of difference can be seen from peak to null - This is more important than the raw gain of the array! Intentionally adding phase delay to one antenna can widen the main lobes to create a larger target and minimize nulls 62
Summary BIP/BOP BOP useful for gaining high angle lobe from a 2 high stack at the sacrifice of only 3db of max stack gain This could be a secret weapon in SS and NAQP contests A high stack can be made to act like its close to the ground 63
Summary - Pattern Stacks can clean up high angle unwanted lobes Separation space and boom length are closely related Always model the intended stack for lobe anomalies due to spacing Rotating an antenna 90 degrees or 180 degrees is an effective way Intentionally slurring a pattern can increase the target area 64 to beam in two or three directions at once.
Example - 40 meter stack 65 How does a 3 ele full size 40 meter beam compare to a stack of shorty 40 meter beams like the CC 420?
Example - 40 meter stack 66 12.56 dBi @ 13 degrees 145’ 3 ele 40m full size 12.54 dBi @ 14 degrees 99.8% efficient
Example - 40 meter stack 68 13.08 dBi @ 16 degrees +.54 dB over full size Shorty 40 Stack, 145/70’
Example - 40 meter stack 68 13.08 dBi @ 16 degrees +.54 dB over full size 12.54 dBi @ 14 degrees
Summary - 40 meter stack Shorty 40 stacks are VERY effective in gain and pattern Shorty 40 stacks equals or betters a single 3 element full A full size 40 stack RULES but a shorty 40 stack is not bad! 69 Shorty 40 stacks have better pattern than a 3 ele FS beam More flexibility, beam in two directions, more angles Much easier to maintain size 40m beam
Other Benefits of Stacking Snow, Rain, wind, ionization static can be eliminated or reduced by taking the top antenna out of a stack Corona discharge points are on the top beam 70
W7GG 180 ft rotating tower 3 - KT34XAs 2 - 3 ele full size 40s 71