22nd Jan 2021... Derek G4CQM skilfully uses YO7 and AOP (professional versions software) from Brian Beezley K6STI to design a comprehensive and superior range of VHF/UHF yagis including several AOWA (Advanced OWA) designs. Lower Q yagis offer greater stability in bad weather and should be considered a priority in extreme weather environments.
The yagi designs with specifications listed below are available as ready made hand built PowAbeam Antennas and must be ordered directly from Roger Banks GW4WND at The DXShop in Montgomery Powys, SY15 6TP... Meanwhile those of you requiring kits and parts to build your own should contact by email Richard Mason G6HKS...
Avoid confusion when ordering from either Roger or Richard, and send them the Design ID link for the yagi build you require!
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| ELEMENT SIZES: All 50MHz designs use 5/8 Inch OD tube elements, driven and parasitics... | |||||||||
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| Design ID | Elements | λ | BW Az° | BW El° | Gain dBi | F/B dB | Efficiency % | Avg Q | DXShop link |
| 6M4WB | 4 | 0.34 | 60 | 90 | 8.64 | 16.07 | 99.2 | 21.85 | 6m4wb |
| 6CQM5UC | 5 | 0.47 | 62 | 93 | 8.60 | 16.97 | 99.7 | 6.3 | 6cqm5uc |
| 6CQM6UX | 6 | 0.71 | 54 | 72 | 10.24 | 22.77 | 99.3 | 21.69 | 6cqm6ux |
| 6M5N50LY | 5 | 0.80 | 50 | 62 | 11.07 | 15.12 | 99.2 | 29.87 | 6m5n50ly |
| 6CQM7UX | 7 | 1.15 | 48 | 58 | 11.72 | 25.21 | 99.2 | 20.53 | 6cqm7ux |
| 6CQM8UC2 | 8 | 1.32 | 44 | 51 | 12.47 | 19.96 | 99.1 | 8.18 | 6cqm8uc2 |
| 6M7N50LY | 7 | 1.67 | 41 | 46 | 13.22 | 23.48 | 99.1 | 26.40 | 6m7n50ly |
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| ELEMENT SIZES: All 70MHz designs use 5/8 Inch OD tube elements throughout, except for 4M5N50U and 4M6N50U (lightweight portable antennas) using 3/16 Inch rod parasitics... | |||||||||
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| Design ID | Elements | λ | BW Az° | BW El° | Gain dBi | F/B dB | Efficiency % | Avg Q | DXShop link |
| 4CQM5UC | 5 | 0.47 | 62 | 92 | 8.62 | 16.89 | 99.7 | 5.18 | 4cqm5uc |
| 4M5WB | 5 | 0.63 | 55 | 73 | 10.02 | 22.94 | 99.1 | 24.67 | 4m5wb |
| 4M5N50U | 5 | 0.7 | 53 | 69 | 10.41 | 24.86 | 98.0 | 27.81 | 4m5n50u |
| 4M5N50SX | 5 | 0.75 | 50 | 63 | 10.97 | 16.64 | 99.2 | 35.37 | 4m5n50sx |
| WS47116 | 7 | 1.15 | 48 | 58 | 11.68 | 25.60 | 99.0 | 20.02 | ws47116 |
| 4M6N50U | 6 | 1.16 | 45 | 53 | 12.14 | 21.44 | 97.0 | 49.80 | 4m6n50u |
| 4CQM7F | 7 | 1.16 | 46 | 55 | 12.00 | 23.44 | 99.2 | 13.87 | 4cqm7f |
| 4M7N50LY | 7 | 1.67 | 40 | 46 | 13.27 | 22.50 | 99.3 | 18.37 | 4m7n50ly |
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| ELEMENT SIZES: All 144MHz designs use 3/16 Inch rod parasitics and 5/8 Inch OD driven element... | |||||||||
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| Design ID | Elements | λ | BW Az° | BW El° | Gain dBi | F/B dB | Efficiency % | Avg Q | DXShop link |
| CQM5UC | 5 | 0.47 | 62 | 93 | 8.60 | 16.95 | 99.5 | 3.84 | cqm5uc |
| CQM7F | 7 | 1.42 | 45 | 52 | 12.37 | 19.11 | 98.6 | 5.79 | cqm7f |
| WS28162 | 8 | 1.62 | 41 | 46 | 13.12 | 24.13 | 97.9 | 17.4 | ws28162 |
| CQM9C4X | 9 | 1.92 | 40 | 46 | 13.42 | 26.84 | 97.7 | 30.96 | cqm9c4x |
| CQM9C4 | 9 | 2.13 | 40 | 45 | 13.71 | 25.31 | 98.1 | 9.4 | cqm9c4 |
| WAXXX10S | 10 | 2.36 | 37 | 41 | 14.21 | 30.70 | 98.0 | 36.29 | waxxx10s |
| CQM0211 | 11 | 3.00 | 33 | 36 | 15.17 | 37.03 | 97.2 | 23.9 | cqm0211 |
| 144NX13S | 13 | 3.85 | 31 | 33 | 16.01 | 32.08 | 97.6 | 23.9 | 144nx13s |
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| ELEMENT SIZES: All 432MHz designs use 3/16 Inch rod parasitics and 5/8 Inch OD driven element... | |||||||||
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| Design ID | Elements | λ | BW Az° | BW El° | Gain dBi | F/B dB | Efficiency % | Avg Q | DXShop link |
| WS715446 | 15 | 4.46 | 28 | 30 | 16.61 | 28.00 | 98.4 | 9.2 | ws715446 |
| WS718562 | 18 | 5.62 | 26 | 28 | 17.38 | 31.03 | 98.2 | 21.7 | ws718562 |
| WS722706 | 22 | 7.06 | 25 | 26 | 18.13 | 32.76 | 98.0 | 31.56 | ws722706 |
| ELEMENT SIZES: WS26075, CQM7C4 and CQM12UX 144MHz designs all use 3/16 Inch rod parasitics and 5/8 Inch OD driven elements... | |||||||||
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| Design ID | Elements | λ | BW Az° | BW El° | Gain dBi | F/B dB | Efficiency % | Avg Q | DXShop link |
| WS26075 | 6 | 0.75 | 54 | 72 | 10.25 | 21.28 | 98.5 | 21.48 | ws26075 |
| CQM7C4 | 7 | 1.16 | 48 | 59 | 11.62 | 26.01 | 98.1 | 28.21 | cqm7c4 |
| CQM12UX | 12 | 2.34 | 37 | 41 | 14.16 | 23.07 | 98.6 | 4.78 | cqm12ux |
| ELEMENT SIZES: WS8C9 144MHz (heavy duty) design uses 5/8 Inch OD tube elements throughout... | |||||||||
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| Design ID | Elements | λ | BW Az° | BW El° | Gain dBi | F/B dB | Efficiency % | Avg Q | DXShop link |
| WS8C9 | 8 | 1.64 | 44 | 50 | 12.81 | 24.71 | 99.4 | 17.53 | ws8c9 |
Derek G4CQM describes two easy methods that make Direct Feed using a simple Split Dipole not only feasible but also work very effectively...
| 1. Nickel-Zinc (NiZn) ferrite optimised for operation at VHF frequencies! | |
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On the Short Wave bands your coaxial cable feeder length may be similar to the λ in question or a few multiples thereof. Under certain conditions the screen itself can display a degree of resonance. It is likely therefore that the use of a balun may be required and of benefit in eliminating radiation from the feeder and prevent it from becoming part of the aerial. However, on the VHF bands a balun may not be required and in fact introduce unnecessary and additional losses. The most important consideration with any yagi beam is that the driven element is tuned and matched correctly. With a real 50Ω yagi this is very easy to achieve directly during the design process. Meanwhile keeping reactance low at the band edges particularly the HF end is paramount for proximity and bad weather stability. If you are in any doubt a simple solution is the use of suitable slip on or clip over ferrite placed close up to the feedpoint. This will impede the flow of RF current on the outer surface of the screen. Clip on ferrite sold in many electronic outlets and mail order catalogues may not be ideal. Most are made from Manganese-Zinc or Iron powder and have little effect at VHF frequencies (100MHz or higher). Instead using Nickel-Zinc (NiZn) ferrite optimised for operation at VHF frequencies is a far better choice! |   |
| 2. The λ/4 Half-Loop Trick! | |
Back in 1976 I attended an international electronics exhibition in Paris and had a meeting with the famous Mark Tonna F9FT. Mark showed me a very simple trick avoiding the need for a balun or ferrite on your 144MHz yagi feeder! Seen opposite λ/4 Half-Loop Trick used on WS8C9! NB The λ/4 half-loop trick will only work on a metal boom! |  |
As a warning the Coiled-Coax Balun sometimes refered to as a Choke Balun is promoted by several commercial outlets and designers, probably because it appears as such an easy solution. Set up correctly the coil self-inductance and distributed self-capacitance resonate as a parallel trap whose high impedance inhibits unwanted shield current. Regrettably most commercially available Choke Baluns have not been tuned properly, indeed can give rise to a whole host of anomalies as it becomes part of the aerial!
Finally, always keep your feeder cable securely taped to the boom/stub mast and keep its path out of the plane of the elements along with any other metallic support structures. Avoid random loops near to the driven element!
DL6WU based stacking calculator, simply enter the -3dB Beam Width (Degrees)...
| Opens in new window! |
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Richard G6HKS demonstrates his measurement of Sun Noise using 4 x WS718562 yagis at a time of low solar activity (2.8GHz flux at 68). Some well known competitor antennas tested were unable to register an S Meter reading at all!
When conducting tests odd quarter waves in the feedline should be avoided otherwise impedance transformation can magnify fault conditions when a system problem exists! Insertion of a temporary quarter wave coaxial cable section (343mm with Vf of 0.66) into the feedline at the shack end will reveal if a fault condition/problem is present... If no fault exists then introducing the quarter wave section will make no difference to measured SWR... On the other hand the temporary quarter wave section can make an improvement indicating a system fault. To be certain do this test when the antenna is dry and then wet!
To reduce screen clutter, YO7 does not label the figures displayed within the Yagi patterns. They are as follows (shown in yellow font):
1. Frequency
2. Forward Gain
3. Front-to-Rear Ratio
4. Input Impedance
5. Standing-Wave Ratio
6. Elevation Angle or Gain FOM
YO displays elevation angle for Yagis over ground and gain figure-of-merit for single-Yagi, free-space models.
YO defaults to a generalized definition of front-to-back ratio.
The notation 12.7-j15.4 means a resistance of 12.7 ohms in series with a reactance of -15.4 ohms.
Z stands for impedance.
The lambda symbol (λ) means wavelengths.
YO uses a generalized notion of standard front-to-back power ratio to characterize pattern quality. Conventional F/B is the ratio of forward power (at 0 degrees) to that radiated in the opposite direction (at 180 degrees).
YO's generalized F/B is the ratio of forward power to that radiated within a specified region to the rear of the antenna. This is called front-to-rear ratio (F/R).
Yagi designs maximizing conventional F/B often have large backlobes at angles other than 180 degrees. Much better patterns result when you optimize a Yagi for F/R.
The F/R region begins at 180 degrees and extends forward to a specified angle (90 degrees by default).
Finally... Element lengths shown in the tables are half lengths.
AO displays wire losses in dB.
AO also displays antenna efficiency in percent. This figure includes the effects of both wire and load losses.
