2.
UHF Vertical 8-Bay Dipole - NO Reflector (13 Feb 2013)UHF Vertical 8-Bay using FAT Dipoles (NO Reflector) analyzed using 4nec2.
Dimensions per Bouval's DIY posts starting with this one: http://www.digitalhome.ca/forum/showthread.php?p=1469742
Original (9.75"x9.625"): SWR Max = 3.1. Max Raw Gain = 14 dBi, but significant Gain Loss on channels in mid-40's & above.
Mod1 (6.75"x9.625"): First optimization to fix Gain Loss problem considered simply cutting off the Dipole Tube ends .
This yielded a fairly flat frequency response curve, except for some loss on lowest freqs and higher SWR on highest freqs.
Mod1: SWR Max = 3.3. Raw Gain = 9.8 dBi (470 MHz), 12.0 (674 MHz), 11.0 (698 MHz).
So a classic trade-off of Gain for wider Bandwidth. Mod1 provided higher Gain on 698 MHz than Mod2a or Mod2b below.
Mod2: Second optimization found optimum Dipole Tube length while modifying the Feedline Separation and position of
the Crossover relative to each OUTER Dipole. Bouval's Dipole-to-Dipole Separation=9.625-in was NOT changed.
By adjusting optimization parameters it is possible to influence the relative importance of Gain vs SWR:
Mod2a (7.0"x9.625"): SWR Max = 3.2. Raw Gain = 9.8 dBi (470 MHz), 12.0 (674 MHz), 11.0 (698 MHz).
Mod2b (8.0"x9.625"): SWR Max = 2.1. Raw Gain = 8.7 dBi (470 MHz), 13.2 (674 MHz), 8.7 (698 MHz).
So Mod2a provides "flattest" freq response while Mod2B provides highest Max Gain but at expense of high/low freqs.
Mod3: Third optimization found optimum Dipole Tube length while modifying the Feedline Separation and position of
the Crossover relative to each OUTER Dipole. Dipole-to-Dipole Separation was also allowed to change in this
more generalized optimization search process to compare an "optimum" configuration to the above alternatives.
To minimize Azimuthal Pattern asymmetries, Crossovers alternate as to whether Right or Left Feedline Wire
hops positive or negative on X-Axis.
Provides excellent SWR with more Gain on highest freqs to overcome extra loss in the Balun, Coax and (if used)
RF Splitter(s), although maybe more than needed for a mast-mounted Preamp with only Balun Loss a significant factor.
Mod3 (8.0"x8.5"): SWR Under 1.8. Raw Gain = 9.1 dBi (470 MHz), Max = 13.8 (686 MHz), 13.4 (698 MHz). |
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