490-MHz Flat-Swept SBGH (Single-Bay Grey-Hoverman), Horizontally-Polarized OMNI-Directional Antenna was analyzed using 4nec2 after Optimization by nikiml's Python Scripts.
Min Gain = 7.2 dBi, Max Gain = 9.3 dBi. This H-Pol. Antenna provides OMNI+PLUS Azimuthal Pattern (Greater than 0 dBd = 2.15 dBi Gain in every direction), with a MINIMUM Gain of 7.2 dBi or MORE on ALL Azimuths. It is well matched to a Characteristic Impedance of 200-ohms, requiring the use of a 4:1 Balun (usually Coax type) to match 50-ohm Load with an SWR of less than 1.5:1, which is well within a typical Transmitter Limit of 2:1.
Although specifically designed for an 8-MHz bandwidth DVB-T Ch23 Micro-Transmitter, the dimensions can be Rescaled to any desired Center Frequency by Fraction F = New Freq / 490 MHz [Smaller for Higher Freqs].
Adequate signal levels very close to Transmit Tower were also analyzed, since higher Gain Antennas may have an Elevation Gain Pattern that is TOO narrow with only minimal signal level being directed DOWN to nearby homes. The Elevation Pattern only has a few degrees where the Gain drops below -20 dBi at about 36-deg Down Look Angle. This should NOT be much of a close-in Coverage problem (if at all) with this Antena, bearing in mind that signal levels are 20 dB HIGHER at 0.1 km as they are at 1 km, as the Path Loss decreases ever closer to the Tower.
EDIT (23Mar2016): Replaced SIDE VIEW with FLAT VIEW Dimensioned Drawing for Each Zig-Zig.
EDIT (13Apr2016): Updated Spread Sheet, adding Double (Crossed) Diamond (Quad) Array performance and SNR Margin (et. al.) Calculation for Dipole Triad Array vs Flat-Swept SBGH.
EDIT (14Apr2016): Updated Spread Sheet, adding estimate for Analog PAL Required SNR.
21 Feb 201626 items3299 visitsAlbum by holl_ands
enlarge 49KB, 554x1024 1 490 MHz Flat-Swept SBGH OMNI 3D View
enlarge 133KB, 380x1024 2 490 MHz Flat-Swept SBGH OMNI Front View [1 large square = 5-inches]
enlarge 222KB, 776x1024 3 490 MHz Flat-Swept SBGH OMNI Top View [1 large square = 1.25-inches] Feedpoint Gap = 0.5-in Max Separation for Outer Apexes = 10.5-in Max Separation for Inner Apexes = 9.125-in
enlarge 182KB, 1152x703 4 490 MHz Flat-Swept SBGH OMNI 486-494 MHz Raw Gain = 9.2 to 9.3 dBi 486-494 MHz F/B & F/R Ratio = 1.1 to 1.2 dB
enlarge 207KB, 1152x703 5 490 MHz Flat-Swept SBGH OMNI 486-494 MHz SWR (200-ohms) Under 1.5 [EVAL calculates Under 1.2]
enlarge 325KB, 1024x1024 7 490 MHz Flat-Swept SBGH OMNI Azimuthal Gain at 486 MHz
enlarge 325KB, 1024x1024 8 490 MHz Flat-Swept SBGH OMNI Azimuthal Pattern at 490 MHz
enlarge 327KB, 1024x1024 9 490 MHz Flat-Swept SBGH OMNI Azimuthal Pattern at 494 MHz
enlarge 325KB, 1024x1024 10 490 MHz Flat-Swept SBGH OMNI Elevation Pattern at 486 MHz
enlarge 325KB, 1024x1024 11 490 MHz Flat-Swept SBGH OMNI Elevation Pattern at 490 MHz
enlarge 328KB, 1024x1024 12 490 MHz Flat-Swept SBGH OMNI Elevation Pattern at 494 MHz
enlarge 255KB, 1024x742 13 490 MHz Flat-Swept SBGH OMNI Antenna Look Down Angle versus Tower Height Advantage (meters) [Difference between Tower and RX Antennas]
Viewers close to Tower have additional Look Down Loss, but MUCH lower Path Loss, so NOT a PROBLEM.
Only a few degrees of Elevation Angle affected when Advantage over 40-m [so don't DO that].
enlarge 169KB, 768x1024 14 490 MHz Flat-Swept SBGH OMNI FLAT View [1 large square = 5-inches]
enlarge 133KB, 768x1024 15 490 MHz Flat-Swept SBGH OMNI Top View [1 large square = 1.25-inches]
enlarge 30KB, 791x1024 16 490 MHz Flat-Swept SBGH OMNI 4nec2 File includes Summary of Dimensions
enlarge 26KB, 791x1024 17 490 MHz Flat-Swept SBGH OMNI EVAL Performance Summary vs Frequency
enlarge 22KB, 791x1024 18 490 MHz Flat-Swept SBGH OMNI EVAL Performance Summary vs 8 Cardinal Angles
