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A-D DB-2 with Reflector (30 Jan 2012)Antennas Direct DB-2 with Reflector analyzed using EZNEC file posted by Ken Nist, as modified to run with 4nec2:
http://www.hdtvprimer.com/SIMS/ [Note: Nist's long Twinlead was deleted.]
AWG6 BowLength = 6.3-in, Bowtie Spacing = 7.8-in, Tine Separation = 4.0-in. AWG12 Feedline Separation = 1.7-in.
Angled Screen Reflector 12.8"H x 19.1"W, with outer 1-in bent forward and is 4.0-in from center of Bowties (Grid = 1"H x 2.55"W).
UHF Raw Gain = 2.8 dBi on Ch14, 8-11.5 dBi on higher channels. UHF SWR is under 2.5
Whiskers (Length=6.25-in) are TOO SHORT, resulting in a sharp Raw Gain drop off on Ch14.
Hi-VHF Raw Gain is higher towards the REVERSE (4-6.8 dBi) and up to -4 dBi (Negative Gain) FORWARD. Hi-VHF SWR is EXCESSIVE. |
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 | 2.
M2 (9.5"x9.0") 2-Bay w Var. Reflectors (31Jan2011)Super-Sized M2 (9.5"x9.0") 2-Bay Bowtie antennas with various alternative reflectors analyzed using 4nec2.
Reflector Separation for all simulations is 4.5", measured from centerline of Bowties.
No SWR reoptimization (e.g. readjust Feedline Separation) has been performed, so there may be room for minor improvements.
The single Vertical or Horizontal BBQ Grates were TOO SMALL, giving away several dB of Gain, but might still be useful.
A pair of BBQ Grates (22"x24") provided slightly MORE gain than a Screen Reflector (2"x4" Grid), although SWR increased a bit.
An 18-in diameter "Pizza Pan" Reflector fell in-between the one and two BBQ Grate alternatives.
Note that a somewhat larger 2-Bay would have improved Raw Gain and SWR performance on the lower frequencies
with minor or no impact on higher frequencies.
Screen reflector (24"x24") using 2"H x 4"W grid was compared to various alternatives based on one or two
11"x25" BBQ Grates (Lowes #201757):
a) M2 (9.5"x9.0") 2-Bay, 24"x24" Grid Reflector: UHF Raw Gain = 9.9 to 13.2 dBi with SWR under 2.4.
Hi-VHF (Ch7-13) Raw Gain = 6.9 to 3.1 dBi but SWR is EXCESSIVE.
b) M2 (9.5"x9.0") 2-Bay, One Horizontal 11"x25" BBQ Grate: UHF Raw Gain = 6.8 to 9.8 dBi with SWR under 2.7 thru Ch51.
c) M2 (9.5"x9.0") 2-Bay, Two Horizontal 11"x25" BBQ Grates: UHF Raw Gain = 7.3 to 9.3 dBi with SWR under 2.3 thru Ch51.
d) M2 (9.5"x9.0") 2-Bay, One Vertical 11"x25" BBQ Grate: UHF Raw Gain = 8.7 to 11.3 dBi with SWR under 3.0.
e) M2 (9.5"x9.0") 2-Bay, Two Vertical 11"x25" BBQ Grates: UHF Raw Gain = 10.6 to 13.3 dBi with SWR under 3.0.
f) M2 (9.5"x9.0") 2-Bay, Two BENT Vertical 11"x25" BBQ Grates: UHF Raw Gain = 10.6 to 13.3 dBi with SWR under 3.1.
Hi-VHF (Ch7-13) Raw Gain = 3.7 to 4.5 dBi but SWR is EXCESSIVE.
g) M2 (9.5"x9.0") 2-Bay, 18" Pizza Pan Reflector: UHF Raw Gain = 8.9 to 9.4 dBi with SWR under 2.5. |
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