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H+U 2Sq-Centipede-In-BoxedTwinRectLoop (12 Nov 2013)Hi-VHF+UHF 2-Square Centipede Inside Boxed-Twin-Rectangular-Loop (NO Reflector)
analyzed using 4nec2.
UHF Raw Gain = 7.5 to 10.6 to 7.6 dBi and SWR (300-ohms) under 2.1. [Excellent]
Hi-VHF Raw Gain = 4.8 to 5.2 dBi and SWR (300-ohms) under 1.9. [Excellent]
Based on 4nec2 file posted by MagiMaster on 8Nov2013, plus my mods to add FR+RP
Plotting Statements and add Rsrc to Tweak AGT (was off by only 0.1 dB):
http://www.digitalhome.ca/forum/showthread.php?p=1881665
Plus Horizontal Elements connected to SOURCE Wire that turn it into Bokabob's Centipede-1:
http://www.digitalhome.ca/forum/showthread.php?p=1053924
For this improved version, I also "Boxed In" the Rectangular Loop, shrinking the interior
whilst also adding an additional "Top Hat". When running nikiml's Python Optimization Scripts,
I allowed the Inner Antenna to slide up and down within the Rectangle until it was clear that
the "best" solution was perfectly centered (e.g. Zs=0.0), so the upper & lower parts are Twins.
Numerous "trials" were observed to have been discarded because the Python Scripts detected an
Overlap between the Outer & Angular Bars if they were within about 1/4+ inches. But since
Z-Coordinates would need to be matched to AT LEAST two and probably more decimals, random
picks didn't stumble into a condition where the Scripts would detect the Intersect...so I
forced it as depicted below.
A significant Loss of Gain on 470 MHz was the only disadvantage of the forced Intersect.
Running a 4nec2 Parameter Sweep on the Gain Peak frequency revealed that the best Gain
occurred when Outer and Angular Bars were very close....but NOT connected. |
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 | 2.
HiVHF+UHF 2SqCentipede-In-RectLoop - OPT (11 Nov 2013)Hi-VHF+UHF 2-Square Centipede Inside Rectangular Loop (NO Reflector) analyzed using 4nec2.
UHF Raw Gain = 6.3 to 9.7 to 6.5 dBi and SWR (300-ohms) under 2.3 [Excellent].
Hi-VHF Raw Gain = 4.7 to 5.0 dBi and SWR (300-ohms) under 2.3 [Excellent].
Based on 4nec2 file posted by MagiMaster on 8Nov2013, plus my mods to add FR+RP
Plotting Statements and add Rsrc to Tweak AGT (was off by only 0.1 dB):
http://www.digitalhome.ca/forum/showthread.php?p=1881665
Plus Horizontal Elements connected to SOURCE Wire that turn it into Bokabob's Centipede-1:
http://www.digitalhome.ca/forum/showthread.php?p=1053924
In a similar fashion to the Bowtie-In-Rect-Loop and 2-Bay-In-Rect-Loop models, in addition
to the SYmbol Variables for the Inner Antenna, I also allowed the Inner Antenna to slide
up and down within the Outer Rectangle when running nikiml's Python Optimization scripts.
When the Inner Antenna was centered nearly an inch higher than the centerline,
the Beam was directed slightly Upwards, but only on 506 +/- 12 MHz, otherwise it was
directed towards the Horizon. |
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 | 3.
HiVHF+UHF 2Sq-Chireix-In-BoxedRectLoop (12 Nov 2013)Hi-VHF+UHF 2-Square-Chireix-In-Boxed-Rectangular-Loop analyzed using 4nec2.
UHF Raw Gain = 6.7 to 9.4 to 5.5 to 7.2 dBi and SWR (300-ohms) under 2.4 (EXCL).
Hi-VHF Raw Gain = 4.2 to 4.7 dBi and SWR (300-ohms) under 3.0 (a bit high)
Based on a post by MagiMaster on 12Nov2013:
http://www.digitalhome.ca/forum/showthread.php?p=1886162
I added the usual set of RP/FR Plotting Statements and did an AUTOSEG(21) so that AGT=1.0. |
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 | 4.
HiVHF+UHF M4 (9.5x9) Bowtie-In-RectLoop (16 Nov 2013)Hi-VHF+UHF 4-Bay Bowtie (mclapp M4 with 9.5x9.0-in sizing, ALL AWG10) Inside a
36-in H x 24-in W Rectangular Loop (0.5-in equiv. O.D. assumed) analyzed using 4nec2.
UHF Raw Gain = 8.1 to 12.2 dBi and SWR (300-ohms) under 3.8 [FAIR].
Hi-VHF Raw Gain = 4.3 to 4.7 dBi and SWR (300-ohms) under 4.0 [FAIR].
For Assumed ALL AWG10 Wire Size. Larger AWG8 (i.e. three AWG12 wires twisted together)
or 3/4-in Aluminized Mylar Tape would have significantly lower SWR.
Compare to M4 (9.5x9) Super-4-Bay (NO Reflector):
UHF Raw Gain is 8.5-12.2 dBi and SWR under 4.0 [ FAIR].
Hi-VHF Raw Gain is 3.5 dBi and SWR under 2.7 [EXCELLENT].
See mclapp's posted drawings, as optimized for New UHF Band (Ch14-51), using
1/8-in = AWG8 elements and AWG12 feedlines
[Element Radius is NOT Critical]: http://m4antenna.eastmasonvilleweather.com/index.html
Website re DIY Construction: https://sites.google.com/site/maycreates/ota-setup/mclapp-4
The Outer Rectangular Loop acted as a RESONATOR, actually improving Hi-VHF Raw Gain about 1 dB.
Hi-VHF SWR was degraded from 2.7 (max) to 4.0, which is a bit high. UHF was only degraded 0.5 dB
on the lowest channels and SWR was just a bit higher.
Since wall mounting a Picture might not put the Max Gain toward desired stations, Raw Gain
Charts have also been provided at various angles offset from straight forward, bearing
in mind that signals might be strong enough to overcome significant off-beam attenuation. |
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 | 5.
HiVHF+UHF M2 (9.5x9) Bowtie-In-RectLoop (16 Nov 2013)Hi-VHF+UHF 2-Bay Bowtie (mclapp M2 with 9.5x9.0 sizing) Inside 36-in H x 24-in W Rectangular Loop
(0.5-in equivalent O.D.) analyzed using 4nec2.
UHF Raw Gain = 5.0 to 10.0 dBi and SWR (300-ohms) under 2.8 [Excellent].
Hi-VHF Raw Gain = 3.9 to 4.4 dBi and SWR (300-ohms) = 9.1 to 6.6 [Excessive].
Compare to 2-Bay WITHOUT the Outer Rectangular Loop:
UHF Raw Gain = 5.7 to 9.7 dBi and SWR (300-ohms) under 3.2 [FAIR].
Hi-VHF Raw Gain = 2.2 to 2.5 dBi and SWR (300-ohms) = 13 to 7 [EXCESSIVE].
The Outer Rectangular Loop acted as a RESONATOR, actually improving Hi-VHF Raw Gain on
higher channels by 0.3 dB, but reducing Raw Gain on lower chanels by 0.7 dB.
Hi-VHF SWR was somewhat improved, but still Excessive. There were only minor UHF changes.
Since wall mounting a Picture might not put the Max Gain toward desired stations, Raw Gain
Charts have also been provided at various angles offset from straight forward, bearing
in mind that signals might be strong enough to overcome significant off-beam attenuation. |
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 | 6.
HiVHF+UHF 4Antlers-In-TwinRectLoop - OPT (11 Nov 2013)Hi-VHF+UHF 4-Antlers Inside Twin-Rectangular-Loop analyzed using 4nec2.
UHF Raw Gain = 7.8 to 5.0 to 9.9 to 9.5 dBi and SWR (300-ohms) under 4.7 (Excessive at 470 MHz).
Hi-VHF Raw Gain = 4.2 to 4.7 dBi and SWR (300-ohms) under 2.5 (Excellent).
From "Framed10.nec" 4nec2 File post#30 by MagiMaster on 9Nov2013:
http://www.digitalhome.ca/forum/showthread.php?p=1882937
I modified to add FR+RP (Plotting) Statements and Rsrc to Tweak AGT=1.0. |
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 | 7.
HiVHF+UHF 2Sq-Chireix-In-RectLoop - OPT (11 Nov 2013)Hi-VHF+UHF 2-Square Chireix Inside (3-ft H x 2-ft W) Rectangular Loop (NO Reflector)
analyzed using 4nec2.
UHF Raw Gain = 5.4 to 10.3 to 8.2 dBi and SWR (300-ohms) under 3.7 (a bit high).
Hi-VHF Raw Gain = 4.2 to 4.5 dBi and SWR (300-ohms) = 2.9 to 5.5 (Excessive).
Per nikiml Optimized 4nec2 file posted by MagiMaster on 8Nov2013, plus holl_ands mods
to add FR+RP (Plotting) Statements and add Rsrc to Tweak AGT (was off by only 0.1 dB):
http://www.digitalhome.ca/forum/showthread.php?p=1881665
Provides very good Gain on UHF Band and moderate Gain in Hi-VHF Band, but SWR on
higher channels in UHF Band is a bit high and Excessive in Hi-VHF Band. |
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 | 8.
HiVHF+UHF 2Bay-In-DualRectLoop - OPT (11 Nov 2013)Hi-VHF+UHF 2-Bay Bowtie Inside Dual-Rectangular-Loop (NO Reflector) analyzed using 4nec2.
UHF Raw Gain = 6.7 to 9.4 to 4.6 dBi drops off on higher Channels and SWR (150-ohms) under 3.3,
a bit high.
Hi-VHF Raw Gain = 4.3 to 4.6 dBi and SWR (150-ohms) under 2.5. [Excellent}
SWR (300-ohms) in both Bands is excessive. If the usual 300-to-75-ohm (4:1) Balun Transformer
is replaced with a 150-to-75-ohm (2:1) Transformer, SWR is greatly improved. Although a special
order item, 2:1 Transformers are available (try for example Mohawk and Allied), including following
MiniCircuits p/n's: JTX-2-10T and TX-2-5.
More info re 2:1, 2.25:1 and other Baluns:
http://www.highfrequencyelectronics.com/Archives/Nov04/HFE1104_Sevick.pdf |
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 | 9.
HiVHF+UHF Hourglass-Loop In DualRectLoop (14 Nov 2013)Hi-VHF+UHF Hourglass-Loop Inside Boxed-Dual-Rectangular-Loop (24x36-in) analyzed using 4nec2.
Dimensions were determined using nikiml's Python Optimization Scripts.
UHF Raw Gain = 3.7 to 1.5 to 6.5 dBi and SWR (300-ohms) under 2.0 [EXCELLENT].
Hi-VHF Raw Gain = 4.7 to 4.8 to 4.5 dBi and SWR (300-ohms) under 6.3 [EXCESSIVE].
ERRATA (16Nov2013: Corrected Labels below Charts 22 and above. They erroneously had
Bandwidth, rather than +/- Angle away from Forward, which is half the Bandwidth.
Comments in 4nec2 File were also clarified to use identical description. |
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 | 10.
HiVHF+UHF Bowtie-In-DualRectLoop - OPT (11 Nov 2013)Hi-VHF + UHF Bowtie Inside Dual (Unequal) Rectangular (36-in H x 24-in W) Loop analyzed
using 4nec2. The Whisker Length, Angle and Z-Coordinate location of the Bowtie was allowed
to vary as part of nikiml Python Script Optimization.
UHF Raw Gain Between 2.0 and 3.1 and SWR under 2.9.
Hi-VHF Raw Gain =2.5 to 4.5 dBi and SWR under 3.9 (a bit high).
Although low Gain, Wide Beamwidth can be useful if Picture Frame can not be aimed as needed.
An Elevation Plot revealed that the Gain Pattern was slightly more in the up or down direction
at different frequencies, with the largest difference occurring mid-band in the UP direction
when Bowtie was ABOVE the mid-line (as shown). |
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 | 11.
Hi-VHF (+UHF) Twin Rectangular Loops (12 Nov 2013)Hi-VHF (+UHF) Twin Rectangular Loops (aka "Shorted Rectangle") analyzed using 4nec2.
Hi-VHF Raw Gain = 4.7 to 5.5 dBi and SWR (300-ohms) under 2.7.
UHF Raw Gain = -8.0 to 0.0 dBi is Low but usable Gain for Strong Signals. Even better
45-deg off-axis on many freqs. SWR (300-ohms) under 2.7 [Excellent].
########################################################
Suppose you had a metal picture frame that was 36-in H x 24-in W and desired to turn it
into a Hi-VHF Rectangular Loop Antenna. Fortunately, it isn't necessary to compromise
the structural integrity by cutting into the bottom rail to insert a Balun...because that
results in poor Gain & SWR (see Charts at bottom).
########################################################
It is much better if an Element is added from Left to Right in the middle of the Picture Frame,
with a 3/4-in Feedpoint Gap in it's middle. The same size material (Half-Inch Diameter)
as in the outer Rectangle was assumed in the 4nec2 Model, since NEC2 has a problem
handling intersections with large Wire Size differences...and hence we can't determine
effect of smaller wires......[sorry]
A Parametric Sweep (using 4nec2) determined the "best" location of the Shorted Feedpoint
Element was halfway between the Top & Bottom, forming a TWIN Rectangular Loop,
similar to Twin Circular Loop and Hourglass-Loop. |
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