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UHF Vert 8-Bay Dipole + 43 Pair RR - OPT
1. UHF Vert 8-Bay Dipole + 43 Pair RR - OPT  (1 Sep 2014)
UHF Vertical 8-Bay FAT Dipole with 43 Pairs of Reflector Rods analyzed using 4nec2 after
determining Dimensions using nikiml's Optimization Scripts.
7 Visits
15 Images
Linked Album
holl_ands
UHF 3-Bay FAT Dipoles + 12 Pair RR - OPT
2. UHF 3-Bay FAT Dipoles + 12 Pair RR - OPT  (1 Sep 2014)
UHF 3-Bay FAT Dipoles with 12 Pair of Reflector Rods (narrow Gap in the middle) analyzed using 4nec2 after determining Dimensions using nikiml's Python Optimization Scripts.
6 Visits
21 Images
Linked Album
holl_ands
UHF Cir-Pol 5-Blade Fan
3. UHF Cir-Pol 5-Blade Fan  (29 Aug 2014)
UHF Circularly Polarized 5-Blade Fan analyzed using 4nec2.
23 Visits
48 Images
Linked Album
holl_ands
UHF 3-Bay Fat Dipole + 16 RR - OPT
4. UHF 3-Bay Fat Dipole + 16 RR - OPT  (21 Aug 2014)
UHF 3-Bay Fat Dipole + 16 Reflector Rods analyzed using 4nec2 after determining dimensions
using nikiml's Python Optimization Scripts.  Reflector Rod-to-Rod Separation was presumed
to be 2-in for an existing set of 4 ea Reflector Sub-Assemblies with 4RR each.
42 Visits
24 Images
Linked Album
holl_ands
A-C U8000 8-Bay - 9 Full-Width Refl Rods
5. A-C U8000 8-Bay - 9 Full-Width Refl Rods  (18 May 2013)
Antennacraft U-8000 8-Bay Bowtie, modified for 9 FULL-WIDTH Reflector Rods analyzed using 4nec2
(eliminated 1/4-in Gap between each Pair of Reflector Rods).

Modification reduced F/B & F/R Ratios.

Dimensions from a 4nec2 file posted by 300ohm in April 2011.
561 Visits
20 Images
Linked Album
holl_ands
Ch30 18El FD Yagi + 14RR Corner
6. Ch30 18El FD Yagi + 14RR Corner  (9 Aug 2014)
Ch30 18-Element Folded-Dipole Yagi with 14-Reflector Rod Corner Reflector analyzed using 4nec2,
after determining Dimensions using nikiml's Python Optimization Scripts.
53 Visits
13 Images
Linked Album
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Horiz-Stack FF4+DAR Angled Against Wall
7. Horiz-Stack FF4+DAR Angled Against Wall  (9 Aug 2014)
Horizontally Stack of Free-Form 4-Bay Bowties (2xFF4) with Double Angled Reflectors (DAR) analyzed by 4nec2 when Angled Against a Metal Wall.
72 Visits
36 Images
Linked Album
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UHF Vertical 8-Bay Dipoles + 43RR
8. UHF Vertical 8-Bay Dipoles + 43RR  (7 Aug 2014)
UHF Vertical 8-Bay Dipole Array with 43 Reflector Rods analyzed using 4nec2 after Dimensions determined using nikiml's Python Optimization Scripts.
77 Visits
15 Images
Linked Album
holl_ands
HiVHF+UHF 8-El VEE LPDA
9. HiVHF+UHF 8-El VEE LPDA  (30Jul2014)
Hi-VHF+UHF 8-El "VEE" LPDA (with Shorting Stub) analyzed using 4nec2 after Dimensions
determined using nikiml's Python Optimization Scripts.

Hi-VHF Raw Gain = 7.5 to 7.1 dBi
UHF SWR Raw Gain = 9.6 to 5.4 to 11.1 to 10.3 dBi.

Hi-VHF SWR (75-ohms) Under 2.4
UHF SWR (75-ohms) Under 4.4
and Under 2.7 above 630 MHz.
48 Visits
18 Images
Linked Album
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Hi-VHF+UHF "VEE" Stick Dipole
10. Hi-VHF+UHF "VEE" Stick Dipole  (25 Jul 2014)
Hi-VHF+UHF "VEE" Stick Dipole (No Reflector) analyzed using 4nec2 after using nikiml's Python Optimization Scripts
to determine the "best" Element Length and Forward Swept Angle to "best" cover BOTH Hi-VHF and UHF Bands.
55 Visits
18 Images
Linked Album
holl_ands
UHF Small Rhombic Stack
11. UHF Small Rhombic Stack  (6 Feb 2011)
UHF Small Rhombic Stack analyzed using 4nec2.  Elements are AWG14: 20-in and 20.25-in long. [AWG10 & AWG12 should be similar.]
1297 Visits
17 Images
Linked Album
holl_ands
Hi-VHF Bowties - No Reflector
12. Hi-VHF Bowties - No Reflector  (2 Apr 2010)
Hi-VHF Four-Whisker, Six-Whisker, Enclosed and Indented Bowties analyzed using 4nec2.
Performance on Ch2-6 + FMBand was also analyzed.  They continue to operate as bi-directional Dipoles with low Gain and much higher SWR on the lower channels.

Six-Whisker Bowtie had better Raw Gain than Four-Whisker and much better SWR than either Four-Whisker, Enclosed or Indented Bowties.
Tine Separation is between upper and lower times.

Raw Gain and Azimuthal Gain Patterns were significantly worse for Enclosed and Indented Bowties.
1333 Visits
61 Images
Linked Album
holl_ands
VHF Stick Dipoles incl Horiz.Rabbit-Ears
13. VHF Stick Dipoles incl Horiz.Rabbit-Ears  (24 Nov 2012)
VHF Stick Dipoles of various Length Elements (3/8-in Diameter & 1/4-in Rabbit-Ears in Horizontal configuration)
analyzed using 4nec2.  Overall-Lengths of the longer Stick Dipoles are typical for VHF/UHF Combo Antenna widths.

Note that when matched to the "natural" dipole impedance of 75-ohms, SWR is very narrowband.
Better wideband performance is found when terminate into 300-ohms.  [Raw Gain is unaffected.]

For Ch2 (57 MHz center freq), it's necessary to match a Total Length of 98.5 inches to 75-ohms,
since 300-ohm load yields Excessive SWR.  The resultant Antenna has just barely enough
low SWR bandwidth for Ch2 and should be located at least several inches away from nearby
objects, whether metal or not, to prevent detuning the Antenna.
For the Ch2 & Ch3 narrowband antennas, wire as small as AWG12 provided acceptable SWR
and same Gain as 3/8-in Aluminum.  Twinlead with AWG24 no recommended for Ch2-4 due to poor SWR.

Many/most Rabbit-Ear Antennas can not be extended enough to provide acceptable (under 2.7) SWR on Ch2 & Ch3.
"Best" Gain (only 2 dBi) & SWR (Excessive, under 5) for Hi-VHF Band is when Half-Lengths = 14.5-inches.
Impedance Matching Networks in the Rabbit-Ears base can improve on this SWR...unfortunately
manufacturers' don't want to disclose specs....so don't  expect much of an improvement....

EDIT (16Jun2013): Added Total Length = 98.5 inches for Ch2, matched to 75-ohms, including an example 4nec2 File.

ERRATA (16Jun2013): Corrected "Half-Lengths" to "Overall-Length" in labels on all except first image,
which correctly uses "Half-Lengths" when describing Rabbit-Ears.
979 Visits
21 Images
Linked Album
holl_ands
UHF Stick Dipole - No Reflector
14. UHF Stick Dipole - No Reflector  (14 Feb 2011)
UHF Stick Dipole analyzed using 4nec2.
Characteristic Impedance of 75-ohms resulted in excessive SWR at high and low frequencies.

The last three images illustrate a good 300-ohms match results if the Dipole Length is 20-percent longer:
Each Whisker=5.27-in with Gap=0.75in for Total WIDTH of 11.29-in, which is a HALF-Wavelength at 523 MHz
(just below middle of the band).

Note that very FAT sticks are needed to minimize SWR throughout the entire UHF Band.
Quarter-Inch-Copper-Tubing (QICT) is analyzed here.  (Half-Inch was difficult to model in 4nec2.)
1294 Visits
15 Images
Linked Album
holl_ands
UHF Fractal Bowtie - No Reflector
15. UHF Fractal Bowtie - No Reflector  (21 Jan 2013)
UHF 4th Order Sierpinski Arrowhead (Fractal) Bowtie analyzed using 4nec2.

Three feedpoint geometries were analyzed:
1) End-Fed Anti-Symmetric (mirrored on Centerpoint vice Z-Axis) provided best Raw Gain and SWR,
but SWR was excessive on the lower frequencies, limiting the useful bandwidth.
The sharp dive in the (Forward) Gain curve corresponds to when the Azimuthal Pattern changes into a four-leaf clover,
with minimal Forward Gain...also note that Real Part of Impedance, R(ohm), nose dives down to only 25-ohms,
resulting in a very high SWR peak.  These severely limit the usable bandwidth.

2) End-Fed Symmetric (mirrored on Z-Axis) had poor Raw Gain and SWR identical to End-Fed Anti-Symetric.

3) Center-Fed Symmetric had poor Raw Gain as well as poor SWR.

These antennas would need to be Rescaled to match the desired operating band since they were very poor matches
for existing UHF Band.  SOURCE Wire length should them be varied to obtain best SWR.
869 Visits
18 Images
Linked Album
holl_ands
 
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