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.
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.
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.
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.||71 Visits|
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.
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.
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.]||1290 Visits|
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.
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.
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.)
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.
UHF Bowties - NO Reflector (20 Apr 2010)|
|Five UHF Bowtie variations (with NO Reflectors) analyzed using 4nec2. ALL except Solid Triangle are AWG10.|
Solid Triangle Bowtie: UHF Raw Gain = 3.4 - 6.3 dBi and SWR (300-ohms) under 2.6 [EXCL].
Six-Whisker Tricon Bowtie: UHF Raw Gain = 3.1 - 5.1 dBi and SWR (300-ohms) under 2.0 [EXCL].
Six-Whisker Bowtie: UHF Raw Gain = 3.4 - 5.0 dBi and SWR (300-ohms) under 2.4 [EXCL].
Four-Whisker Bowtie: UHF Raw Gain = 3.2 - 5.3 dBi and SWR (300-ohms) under 3.0 [FAIR].
Enclosed Bowtie: UHF Raw Gain = 3.8 - 5.4 dBi and SWR (300-ohms) under 3.3 [FAIR].
Indented Bowtie: UHF Raw Gain = 3.6 - 5.5 dBi and SWR (300-ohms) under 4.2 [POOR].
Highest Raw Gain was provided by optimized Solid Triangle, about 1 dB higher on highest freqs.
Flattest Gain was (tie) 6-Whisker & Enclosed Bowtie, latter had Highest Gain on Low Channels.
Optimum dimensions determined by nikiml's Optimization Scripts were Hypotenuse=9.75-in,
Tip-to-Tip Vertical Separation=12-in and Feedline Separation=1.0-in. Hi-VHF analysis is also provided.
Six-Whisker had better SWR (300-ohms) than Four-Whisker version.
Tine Separation is measured between upper and lower Whisker Tips.
Quasi-optimum 6-Whisker sizes for ALL AWG10 wire sizes:
All BowLength=10-in, TineSeparation=5-in and Feedline Separation=1.5in.
Total WIDTH is 21.5-in, which is a ONE-Wavelength at 549 MHz (middle of the band).
Contrast this to a Dipole which has minimum SWR of about 75-ohms closer to a HALF-Wavelength.
All models had AGT=1.0 (no Gain correction) with No Warnings or Errors, except for 6-Whisker Bowtie:
4nec2's Automatic Gain Test (AGT) would not go below 0.41 dB (UHF) and 0.29 dB (Hi-VHF).
Subtract these corrections from 6-Whisker 4nec2 Gain results below.
The 6-Whisker Tri-Conn Bowtie did NOT require any AGT corrections.
EDIT (7Sep2011): Added 4-Whisker, Enclosed and Indented Bowties.
EDIT (20Jun2013): Added Solid Triangle Bowtie using 33-Wire Model using nikiml's Optimization Scripts.
See CM4251 Parabolic+2-Bay+Grid-Reflector analysis for alternative 265-Wire Model.
EDIT (18Jul2014): Added 6-Whisker Bowtie with Tri-Conn (Triple Connector) between Whiskers and the Balun Feedpoint. AGT is much easier to adjust.
Hi-VHF+UHF Stick Dipole - No Reflector (24 Jul 2014)|
|Hi-VHF+UHF Stick Dipole (NO Reflector) analyzed using 4nec2.|
Two versions were analyzed:
a) Optimized for Hi-VHF Band,
b) Jointly Optimized for Hi-VHF & UHF Bands, using nikiml's Optimization Python Scripts.
a) Optimized for Hi-VHF Band: Overall Length = 28.2-inches.
Hi-VHF Raw Gain = 1.8 to 2.0 dBi and SWR (75-ohms) Under 2.8.
b) Jointly Optimized for Hi-VHF and UHF Bands: Length = 25.6-inches.
Hi-VHF Raw Gain = 2.0 to 2.2 dBi and SWR (75-ohms) Excessive on Lower Channels.
UHF Raw Gain = 4-5 dBi in lower UHF Band and then rolls off above about 580 MHz.
Lo+Hi-VHF 1-Bay Bowtie (24 Nov 2012)|
|Lo-HiVHF (Ch2-13) 1-Bay Bowtie analyzed using 4nec2 after optimizing via nikimil's Python scripts.|
Provides more Gain than Stick Dipole or Folded Dipole across BOTH Ch2-6 Lo-VHF and Ch7-13 Hi-VHF Bands.
However, narrow beamwidth on Ch7-13 requires careful aiming.
Optimized size is BIG (15.75-ft Wide by 4.25-ft High), using 1/4-in O.D. Copper (may use larger, incl. 3/8-in Aluminum):
Each of Six Whiskers = 92-inches, Top-Bottom Tine Separation = 51-inches & Feedpoint = 5-inches.