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VHF Simple-VEE-Rabbit-Ears
1. VHF Simple-VEE-Rabbit-Ears  (14 Feb 2011)
VHF Simple-VEE-Rabbit-Ears (no matching network) analyzed using 4nec2.

Hi-VHF Band Optimum Whisker Length = 14.75 for Quarter-Inch-Copper-Tubing (QICT) with Feedpoint Gap = 0.75-in.

For 45-degree Angle, Horizontal Polarization Gain was equal to Vertical Polarization Gain across the Hi-VHF Band.

Note: Even a 0.5-inch error in adjusting lengths of Rabbit Ears severely degraded SWR, although only minor impact on Raw Gain.

EDIT (10Sep2011): Added a "What-IF" exercise to illustrate the Raw Gain and SWR (if 300-ohms) from Ch2-13.
Note that SWR in Hi-VHF Band is four time higher than for 75-ohms, and becomes even more excessive on lower freqs,
as the Impedance becomes nearly all Capacitance (negative Reactance).

EDIT (16Jan2012): Added Circular Polarization Azimuthal Plots.  Note that Right Circular = Left Circular at 90-deg & 270-deg Azimuths, so there is very little suppression of Cross-Polarized (e.g. reflected Multipath) signals.

ERRATA (5Sep2014): Uploaded revised 4nec2 File with sin and cos functions reversed to match Angle Definition in Comment description.  Since all charts were for 45-degree Angle, they are NOT affected.
618 Visits
24 Images
Linked Album
holl_ands
UHF Vert 8-Bay Dipole + 43 Pair RR - OPT
2. 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.
56 Visits
15 Images
Linked Album
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UHF 3-Bay FAT Dipoles + 12 Pair RR - OPT
3. 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.
42 Visits
21 Images
Linked Album
holl_ands
UHF Cir-Pol 5-Blade Fan
4. UHF Cir-Pol 5-Blade Fan  (29 Aug 2014)
UHF Circularly Polarized 5-Blade Fan analyzed using 4nec2.
52 Visits
48 Images
Linked Album
holl_ands
UHF 3-Bay Fat Dipole + 16 RR - OPT
5. 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.
69 Visits
24 Images
Linked Album
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A-C U8000 8-Bay - 9 Full-Width Refl Rods
6. 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.
628 Visits
20 Images
Linked Album
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Ch30 18El FD Yagi + 14RR Corner
7. 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.
73 Visits
13 Images
Linked Album
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Horiz-Stack FF4+DAR Angled Against Wall
8. 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.
93 Visits
36 Images
Linked Album
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UHF Vertical 8-Bay Dipoles + 43RR
9. 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.
102 Visits
15 Images
Linked Album
holl_ands
HiVHF+UHF 8-El VEE LPDA
10. 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.
70 Visits
18 Images
Linked Album
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Hi-VHF+UHF "VEE" Stick Dipole
11. 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.
79 Visits
18 Images
Linked Album
holl_ands
UHF Small Rhombic Stack
12. 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.]
1318 Visits
17 Images
Linked Album
holl_ands
Hi-VHF Bowties - No Reflector
13. 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.
1366 Visits
61 Images
Linked Album
holl_ands
VHF Stick Dipoles incl Horiz.Rabbit-Ears
14. 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.
1033 Visits
21 Images
Linked Album
holl_ands
UHF Stick Dipole - No Reflector
15. 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.)
1330 Visits
15 Images
Linked Album
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