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Performance Data and Geometry Pattern and VSWR Download as File Stacking A Review on the 8 Element DK7ZB "OWM" Yagi When DK7ZB announced to turn to "focus on the noise figure" and "develope some models with these fundamentals" I guess that others were excited just like me what he would come up with. Being widely known for good designs we owe him full attention when he introduces a new technique. So, when I noticed that DK7ZB published what he derived at using my "58" as baseline I wanted to see how good it is and if I could do even better with 28 ohms now. Meeting my own skills according the 8 OWL's wave guiding structure it was not that easy, but I grinded of some Kelvins finally without losing but gaining some bandwidth. In this case I think it is quite legitmately to add a bit of fine tuning to a design that goes back on my ideas and is shown off as "Low Noise" and wide band, though DK7ZB did not publish Antenna Temperature or G/T yet. Scroll down to "Stacking" and find Antenna Temps and G/T numbers comparative to the VE7BQH G/T Table with the exception that I used approximately same very high segmentation density that DK7ZB is known for (>30) to be on level with the 8 ele. OWL. Hence numbers given might vary by one or two 10th depending on the chosen segmentation density. But that does not alter the basic directions shown. Current distributions
Element positions Refl DE D1 D2 D3 D4 D5 D6 DG7YBN 58 0 282 403 822 1440 2130 2850 3485 DK7ZB 8 OWL 0 340 505 855 1440 2130 2850 3485 Performance Data of fine tuned 8 ele. 28 ohms version Gain vs. isotr. Rad. 13.15 dBi Gain vs. Dipole 11.00 dBD 3 dB Hplane 41.2 deg. 3 dB Eplane 47.0 deg. F/B 27.82 dB F/R 22.08 dB Impedance 28 ohms Mechan. Length 3485 mm Electr. Length 1.68 λ Stacking Dist. hpol. (DL6WU) toptobottom 2.609 m sidebyside 2.957 mGeometry Note: element lengths for Ø 8 mm fit 5/16" too Use EZNEC's AutoSegmentation at 600 MHz and correct elem. lengths by 2.x mm plus for real builds due to very high segmentation base Pattern and VSWR Plots Elevation plots, Antenna Temps. and G/T  ratio at 144.1 MHz For those, who are less familiar with G/T numbers and Antenna temperatures: The more positve G/T numbers are, the better they come. Example: 10.83 is better then 10.87 [dB]. The SignaltoNoise  ratio is not defined by gain alone, but just by gain/antenna temperature = G/T (s. formula at end of page). Antenne Temp. is captured noise power per band width from all directions in a standardised artificial environment, not the physical temp. of your Yagi. Depending on the real environment a decrease of that T_ant. by 5 Kelvin can make a noticable difference already on the noise floor of your RX.
• View Compared Patterns in larger image RL and SWR plot  DK7ZB 28 ohms interpretation RL and SWR plot  Fine tuned 28 ohms version // You think that less sidelobes, higher G/T designs must be narrower in band width? Downloads EZNEC file of the revised 8 ele. 28 ohms Yagi with Straight Split DE klick Stacking Elevation plot and data of 4 Yagi bays All these 4YagiBays are created using the DL6WU stacking distance formula
Theoretical numbers, no phasing line losses nor imperfections caused by Hframe included *) T_sky = 200 K, T_earth = 1000 K as in VE7BQH G/T table Discussion At first glance DK7ZB's interpretation looks quite impressive as a single Yagi. Since we all are expecting that using 28 ohms usually means more band width and a touch of extra gain. However, it does not work out so well with the DK7ZB interpretation in terms of "Low Noise". It yields more gain then the other two, on the price of more extensive sidelobes. It yields high F/B, which is not all if we design for low noise as the F/R is rather important too here. Consequently the sum of lobes is so much larger that T_ant rises to a number that the extra gain can not stand up against when all is added to the G/T number. Use Gain in dBi, T_ant in Kelvin, logarithms base is 10 Fine tuning using OTHER than just maximisegain principles produces a 28 ohms version that has more bandwidth and and higher G/T than the 50 ohms version. Showing 0.16 dB more gain the 4YagiBay using DK7ZB's interpretation produces the highest Antenna Temperature of all. The G/T is just 0.01 dB over the 50 ohms version  which might be quieter whenever external noise exceeds the mean number of 1000 K for T_earth used in the G/T table. Fine tuning on all parameters produces a much better G/T then pushing gain as a single parameter. OWL / OWA or OWM stand for optimised in whatever discipline. And usually for a band filter like SWR curve. I would not consider naming any of the above real OW... Yagis. They are nice designs with enough bandwidth to act "forgiving" on slightly missed out BC numbers. Thats it. The original Yagi was published in "58 ... an expandable 144 MHz Yagi" in Dubus 4/2012, months prior to DK7ZB's OWM and is listed in the VE7BQH 144 MHz G/T Table since much longer even. 73, Hartmut, DG7YBN 