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UHF Folded & Tri-Folded Dipoles (7 Sep 2011)UHF Folded and Tri-Folded Dipoles analyzed using 4nec2.
UHF Folded Dipole size providing best SWR and Net Gain (New UHF Band):
9.25 x 1.0 inch - Quarter-Inch Copper Tubing (QICT)
9.375 x 1.0 inch - AWG10 Copper Wire |
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Hi-VHF Folded Dipoles (15 July 2009)Hi-VHF Folded Dipoles with wide variance in element sizes analyzed using 4nec2.
Example 4nec2 files included for most antennas.
Here's an on-line Folded Dipole Calculator:
http://www.k7mem.150m.com/Electronic_Notebook/antennas/folded_dipole.html
Note that IF element diameters are the same, impedance does not change as you vary the separation.
By adding a Reflector and a Director, you've got a simple 3-Element YAGI:
http://www.wfu.edu/~matthews/misc/dipole.html
Some DIY Folded Dipole examples:
oldsyd's (new) Ch7: http://img4.imageshack.us/img4/6002/foldeddipole1.jpg
oldsyd's (old) Ch7: http://img23.imageshack.us/img23/180/0000241.jpg
mlord's Ch6: http://www.digitalhome.ca/forum/showthread.php?p=833571
There is a Quasi-optimum Separation between Folded Dipole Elements of about two inches for larger diameters,
one inch for moderate and 1.0 to 0.5 inch for small wires. But a 2:1 variation causes only small differences in SWR.
Hi-VHF sizes providing best SWR and Net Gain (centered on CH9/10) are:
27.0 x 2.0 inch - One Inch Diameter Copper Tubing
27.5 x 2.0 inch - 1/2-in Copper Tubing (Type M)
28.0 x 1.5 inch - 5/16-in O.D. Copper Tubing (not much better than quarter inch)
28.0 x 1.0 inch - Quarter Inch O.D. Copper Tubing (or RG-58/59 Braid Shield Coax)
28.25 x 0.75 inch - AWG12 Copper Wire (may leave insulation on in VHF band)
24.50 x 0.5 inch - AWG24 Copper Wire (may leave insulation on)
[ALL MEASUREMENTS ARE CENTER-TO-CENTER.]
Sizes may be rescaled by same fraction as frequencies change, using LONGER elements for LOWER frequencies.
For example, minimum SWR for AWG12 occurs at 192 MHz (between Ch9&10). To move minimum SWR to 207 MHz (Ch12),
shorten 28.25-in by fraction 192/207 or 26.2-in. Separation between Folded Dipole Elements won't make much difference.
QtrInchCopper Tubing, 1/2-in Type M Copper Tubing and 1-in O.D. provide good SWR across entire Hi-VHF band.
AWG12 and AWG24 are best ONLY over 2 adjacent channels (Ch9-10 example shown).
Total parts cost: about $10 for 10-ft piece of 1/2-in Type M Copper Tubing, 4 Copper Elbows, 2 Caps and a cheap Balun.
FYI: johnrmckee measured 0.5 dB VHF/UHF loss for Philips Outdoor Balun:
http://www.avsforum.com/avs-vb/showthread.php?p=15851345
This is consistent to what I've measured for Radio Shack, RCA and Channel Master Baluns at VHF.
But Philips Outdoor Balun is first one I've seen with low loss across the UHF Band.
So after finishing these NEC Sim runs, I was Googling around for some additional Folded Dipole examples:
Yup, it's 1/2-in Copper Pipe with 4 Elbows: http://pigtail.net/nicholas/ctn/dipole.html
EDIT (22Jun2009): Added photos of DIY construction for a Hi-VHF Folded Dipole using 1/2-in Copper Pipe.
Since he actually had (one and only one) experience brazing a pipe joint....and the tools...my son did this job.
Last week he had to replace a corroded valve on his water heater....making him an expert compared to me....
EDIT (28Jun2009): Hung Hi-VHF Folded Dipole (1/2-in Pipe version) at 7-ft height on Outdoor Pergola 70-miles SE fm Mt Wilson (L.A.).
Ch7/9 very watchable but weak (80-90% QUALITY on Dish vip622 DVR with 65-70% "SIGNAL STRENGTH").
Did not expect Ch11/13 due to Ch12 being only 2.7 miles away and Folded Dipole doesn't have sharp null in requisite direction.
EDIT (3Sep2011): Used 4nec2 to analyze different Feedpoint Gap sizes in a Folded Dipole (L=27.5, OD=0.569-in Cu).
Raw Gain and Net Gain were within 0.1 dB, whether 0.75, 1.0 or 1.45-in, so Gap Size in Unimportant.
BTW: 1.45-in is the Source segment size in the posted 4nec2 file with one continuous driven element. It was not possible
to test 0.5-in Gap size, due to 4nec2 declaring errors due to it's small size, not fixable with different AutoSeg( ) choices.
EDIT (22Nov2012): Moved Ch6 and Vertical FM Charts to new VHF Folded Dipole album. |
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VHF Folded Dipole incl. Ch6 & FM (22 Nov 2012)VHF Folded Dipoles, including specifically for Ch2-6, Ch2-FM, only Ch6 and only FM, analyzed using 4nec2.
Includes Omnidirectional Vertical Dipole for FM Band, but see OMNIDIRECTIONAL album for more info.
Example 4nec2 files included for most antennas.
Some DIY Folded Dipole examples:
oldsyd's (new) Ch7: http://img4.imageshack.us/img4/6002/foldeddipole1.jpg
oldsyd's (old) Ch7: http://img23.imageshack.us/img23/180/0000241.jpg
mlord's Ch6: http://www.digitalhome.ca/forum/showthread.php?p=833571
There is a Quasi-optimum Separation between Folded Dipole Elements of about two inches for larger diameters,
one inch for moderate and 1.0 to 0.5 inch for small wires. But a 2:1 variation causes only small differences in SWR.
Optimized Folded Dipole sizes are:
63.0 x 2.0 inch - 0.569-in (Type M) Copper Tubing (Ch6, also OK for CH5 and FM Band)
65.5 x 0.5 inch - AWG12 Copper Wire (Ch6, but SWR too high for CH5 & FM Band).
66.2 x 0.5 inch - AWG24 Copper Wire (Ch6, but SWR too high for CH5 & FM Band).
[Reduce length by velocity factor if using 1/2-in twinlead.]
76.0 x 2.5 inch - 0.569-in (Type M) Copper Tubing (Ch3-6, although SWR high on Ch3 & Ch6)
82.0 x 2.5 inch - 0.569-in (Type M) Copper Tubing (Ch2-6, although SWR high on Ch2 & Ch6)
Optimum size for an almost OMNIDIRECTIONAL VERTICAL Folded Dipole for just the FM Band is 53.0 x 8.0 inch
using 0.569-in O.D. Copper Tubing. Gain away from feedpoint is 2.6 dBi and 1.4 dBi in opposite direction.
A clamp can be attached to the center of the long element since it is at zero ground potential.
Alternative size for Horizontal or Vertical FM Folded Dipole is 55-in x 4-in. Both use Feedpoint Gap=1.25-in.
Folded Dipoles for FM Band frequently come with a Receiver: http://kgnu.org/ht/helpfm.html
Here's an on-line Folded Dipole Calculator:
http://www.k7mem.150m.com/Electronic_Notebook/antennas/folded_dipole.html
Note that IF element diameters are the same, impedance does not change as you vary the separation.
By adding a Reflector and a Director, you've got a simple 3-Element YAGI:
http://www.wfu.edu/~matthews/misc/dipole.html
EDIT (22Nov2012): Moved Ch6 and Vertical FM Charts to this new Album from Hi-VHF Folded Dipole album.
Added analysis of optimized sizes for Ch2-6 and Ch3-6 Folded Dipoles. |
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UHF Circular & Square Loops NO Reflector (15 July 2009)UHF Circular & Square Loops analyzed using 4nec2.
a) UHF Circular Loop - NO Reflector:
Ken Nist's Loopa.ez (7.5-in diameter, using AWG12) is a good choice for the Old UHF Band.
A better choice for the New UHF Band (470-698 MHz) is 7.75-in diameter, using AWG12.
However, SWR for either is excessive at lowest and highest frequencies.
SWR can be significantly improved by using QICT (Quarter Inch Copper Tubing), with 8.5-in diameter being best size for New UHF Band.
Raw Gain is then 3.6-5.1 dBi, SWR under 2.7.
b) UHF Square Loop - NO Reflector
Optimum size for NEW UHF Band is 6.9-in. Raw Gain is 3.4-4.1 dBi. SWR is under 2.7. Which is lower Gain than the Circular Loop above.
EDIT (6 Sep 2011): Added UHF Square Loop. |
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Hi-VHF Square & Circular Loops (16 July 2009)Hi-VHF Square and Circular Loops are analyzed using 4nec2 to find optimum sizes.
Optimum size for Hi-VHF Square Loop is 20-inches per side (Center-to-Center) for 1/2-in (Type M) Copper pipe (OD=0.569-in),
18.5-inches for 1/4-in Copper Tubing and 16.75-inches for AWG24 wire, which would be less visible in a window.
A 10-ft length of 1/2-in Copper Pipe and four 90-deg Elbows costs about $10. "3/8-in I.D." Copper Coil for Circular Loop is even less.
Optimum size for Hi-VHF Circular Loop is 24-inches Diameter (Center-Center) using "3/8-in" Copper Tubing (actual OD=0.514-in).
Despite smaller diameter, Circular Loop had slightly higher Raw and Net Gain than Square Loop.
Optimum size for Hi-VHF Circular Loop using QICT (QuarterInchCopperTubing) is 23-in, AWG12 is 21.5-in
and AWG26 is 21-inches (very thin to invisibly tape to a window).
EDIT (16Jul2009): Analyzed additional element sizes for Hi-VHF Circular Loop. |
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Hi-VHF Circular Loop + Reflector (15 July 2009)Hi-VHF Circular Loop with either Loop or Screen Reflector analyzed using 4nec2.
With Loop Reflector, Net Gain was 8 dBi on Ch7, dropping to 6 dBi on Ch13 with excellent SWR, except for small increase on Ch7.
Adding Loop Reflector increased Net Gain by 2-4 dB (less at high freqs) with more than 8.7 dB F/B (and F/R) using
Optimum Diameter=24-in for Half-Inch Copper Tubing. Best F/B (and F/R) is on Ch8-10.
Optimum Diameter=23-in for Quarter Inch Copper Tubing (QICT) was nearly as good, with more than 7.3 dB F/B (and F/R).
Smaller Circular Loop Element sizes not analyzed since a Square Loop (Quagi) would be easier to construct.
Loop Reflector dimensions are optimized for full Hi-VHF Band coverage.
Rescaling to optimize Ch7 will have only minor-moderate impact to Ch13 F/B, F/R and SWR.
However, rescaling to optimize Ch11-13 will degrade F/B, F/R and especially SWR on CH7-10.
EDIT (16 Sep 2009): Added analysis of alternative Hi-VHF Loop with Screen Reflector. |
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UHF "Figure-8" Twin Loops - NO Refl (6 Sep 2011)UHF "Figure-8" Twin Circular Loops with NO Reflector analyzed using 4nec2.
Should use 9.1-in Diameter, QICT (Quarter-Inch Copper Tubing) or larger for New UHF Band version (SWR under 2.4, -0.8 dB Mismatch Loss).
AWG10 NOT RECOMMENDED for UHF version, since SWR climbs as high as 3.65 (-1.71 dB Mismatch Loss). |
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Hi-VHF Figure-8 Twin Loops - NO Refl (15 July 2009)Hi-VHF "Figure-8" Twin Circular Loops with NO Reflector analyzed using 4nec2.
Optimum size is 24-in Diameter, using QICT (Quarter-Inch Copper Tubing). |
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UHF Twin-Hoop Chireix - NO or 26ReflRods (18 Aug 2010)UHF Twin-Hoop Chireix with NO or 26 Reflector Rods analyzed using 4nec2.
Used SAME 4nec2 file as Hi-VHF & UHF "Figure-8" Twin Loop, except cut out 1-in Gaps at Top and Bottom of the Hoops.
No doubt due to the much larger size (12.5 vs 9.1-inch), this significantly improved the New UHF Band Gain.
A smaller (10.8-in) diameter would be better for Old UHF Band (up to Ch69).
EDIT (5Sep2011): Added NO Reflector version, optimized for New UHF Band. |
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UHF Shorted Bowtie Loop (SBL) (15 Sept 2009)UHF Shorted Bowtie Loop (SBL) Antenna analyzed using 4nec2.
An SBL is a Loop Antenna with an interior Bowtie acting as a Feedline.
It is compared here to just a Loop as well as just a 6 or 4-Whisker Bowtie. |
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HiVHF Shorted Bowtie Loop (NO Reflector) (18 Sept 2009)Hi-VHF Shorted Bowtie Loop (46-in Diameter using Half-Inch Copper Tubing) analyzed using 4nec2.
Optimized for Hi-VHF Band (Ch7-13) but also provides minimal performance on Ch6 & FM Band.
CH2-5 also have 2.6-3.0 dBi of Raw Gain, but SWR becomes excessive on lowest channels. |
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Hi-VHF Shorted Bowtie Loop (w Reflector) (18 Sept 2009)Hi-VHF Shorted Bowtie Loop (with Reflector) analyzed using 4nec2.
Optimum Loop Diameter = 44-in with Half-Inch-Copper-Tubing for 48-in H x 48-in W Screen Reflector (1"x2" Grid).
This minimum Screen size was determined by size of typically available fencing material.
Angled Reflectors beyond the 48x48 Grid may be added to improve Gain by reducing Horiz. and/or Vert. Azimuthal coverage.
Optimum Diameter for smaller Element sizes may be slightly different. |
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UHF+Hi-VHF Bowtie-In-Loop - NO Reflector (20 Apr 2010)UHF+Hi-VHF Bowtie-In-Loop (BIL) Antenna analyzed using 4nec2. Loop Diameter = 23-in, Whiskers = 10-in.
Based on a design (X0512 aka WW_X0498-Rev2,) by WildWillie on www.digitalhome.ca Antenna R&D Forum.
A simple to build antenna with moderate performance in BOTH UHF and Hi-VHF bands. |
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UHF+Hi-VHF Bowtie-In-Loop (w ReflRods) (19 Sept 2009)UHF+Hi-VHF Bowtie-In-Loop (BIL) Antenna with 19 Angled Reflector Rods analyzed using 4nec2:
X0512 aka WW-X0498-Rev2 design by wildwillie (c), 16Sept2009. Loop Diameter = 23-in, Whiskers = 9-in. |
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HiVHF+UHF Dreamcatcher (20 Feb 2011)Wildwillie's Hi-VHF+UHF Dreamcatcher (Hourglass) Bowtie-In-Loop variant (X0498-Rev2-Wide) analyzed using 4nec2.
Excellent performance on both Hi-VHF and New UHF TV Bands, with some Gain loss & SWR mismatch in the Old UHF Band above Ch51. |
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Hi-VHF Square Loop + Reflector (19 Aug 2011)Hi-VHF Square Loop with 28"x28" Screen Reflector (2"x4" Grid) at 13" Separation analyzed using 4nec2.
Raw Gain = 7.6-7.9 dBi with SWR under 3.0. |
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2-Bay Hentenna NO+11ReflRods (21 Aug 2011)UHF 2-Bay Hentenna with NO Reflector and with 11 Reflector Rods analyzed using 4nec2.
a) UHF 2-Bay Hentenna with NO Reflector:
Analyzed Xauto's version x1052 2-Bay Hentenna: 8.75-in Width x 13-in Height.
Raw Gain = 3.8-5.7 dBi, SWR under 1.8.
b) UHF 2-Bay Hentenna with with 11 Reflector Rods:
dcartier's original 4nec2 file (UHF Gain & SWR Optimized: Score=1.16102) was run for another 30 hours
of optimization (Score=0.660617), using nikiml's Python Scrips, significantly improving F/B & F/R Ratios.
UHF Raw Gain increased about 0.5 dBi. SWR slightly improved from under 2.2 to under 1.8.
F/B and F/R were significantly improved, from a range of 3-7 dB to a range of 7-13 dB.
Hi-VHF Raw Gain was 7.1-5.5 dBi FORWARD and 7.1-8.2 dBi towards the REVERSE.
Unfortunately SWR was very excessive (25-35).
FYI: Temporarily removing GW40 (wire only 0.5-in behind the feedpoint) increases SWR to 4.3.
I've seen this sort of closely coupled "SWR tuning element" technique used in Yagi Antennas,
including the YA-1713:
BTW: I temporarily commented out GW49 & GW50 (small, upper & lower most Reflector Rods)
and reran 4nec2. I was surprised to see that SWR was unchanged, but Gain increased
about 0.5 dBi and F/B & F/R Ratios were slightly improved....so, there may be TOO many
Reflector Rods....go figure....
More (or Fewer?) Reflector Rods may be required to improve the UHF F/R & F/B Ratios...
It is left as an exercise to optimize both UHF and Hi-VHF...preferably, including
both F/R & F/B Ratios explicitly in the "cost function"....longer runs might also help....
EDIT (5Sep2011): Added UHF 2-Bay Hentenna (Square Loop) with NO Reflector. |
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UHF Hourglass Loop (30 Nov 2012)UHF Hourglass Loop analyzed using 4nec2 after finding "best" dimensions using nikiml's Optimizations Scripts.
Based on UHF Hourglass Loop posted by oneolddude in www.digitalhome.ca forum.
However Optimization and Rescaling increased 470 MHz Gain by about 0.5 dB with Max Gain on 698 MHz.
NO Reflector Rods (Search across ALL THREE Variables):
UHF Raw Gain = 4.7-6.0 dBi with Excellent SWR under 1.6, using AWG6.
15Reflector Rods (Search across ALL SIX Variables):
UHF Raw Gain = 9.7-10.7 dBi with SWR under 3.0, using AWG6.
Excellent Front/Back and Front/Rear Ratios = 20 dB or better.
NOTE: Most optimization runs result in Max Gain in mid-band, vice close to 698 MHz.
A narrower parameter search was performed, using a "bestx_xxx.nec" file closest to desired.
Alternative runs with SWR under 2.0 resulted in 0.4 dB lower Gain.
Some resulted in a second Max Gain peak in 700 MHz (LTE) Band, which is to be avoided.
Grid Mesh 24x19.5-in (per 300-ohm post):
UHF Raw Gain = 9.4-10.8 dBi with SWR under 2.4, using AWG6.
Front/Back and Front/Rear Ratios 15 dB or better.
Grid Mesh 24x19.5-in (Re-Optimized using nikiml's Python scripts):
UHF Raw Gain = 9.5-10.6 dBi with SWR under 2.5, using AWG6.
Front/Back and Front/Rear Ratios 17 dB or better.
PS: For improved F/B and F/R Ratios, should try different Grid Mesh sizes.
EDIT (10Dec2012): Added 4nec2 analysis with Grid Mesh (per 300ohm post) and
Re-Optimized version, with somewhat better F/B and F/R Ratios. |
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Hi-VHF Hourglass Loop (30 Nov 2012)Hi-VHF Hourglass Loop analyzed using 4nec2 after finding "best" dimensions using nikiml's Optimization Scripts.
Based on UHF Hourglass Loop posted by oneolddude in www.digitalhome.ca forum.
NO Reflector Rods (Optimized Height, Width & Feedpoint Gap Size):
Ch7-13 Raw Gain = 5.3-6.1 with Excellent SWR under 1.6 (using Quarter-inch Copper Tubing).
Provides about 4 dBi Raw Gain on Ch2-6 and FM Band, but SWR is excessive.
Also provides some Raw Gain with acceptable SWR in UHF Band, but only over mid-band frequencies.
Add 15 Reflector Rods (Optimized Width, Rod-Rod Separation & Separation from Hourglass):
Ch7-13 Raw Gain = 9.7-10.05 dBi with SWR under 3.1 (using Quarter-inch Copper Tubing).
Reflector Total Height = 68-in x Width = 56.5-in.
Excellent Front/Rear (hemisphere) Ratio = 32-34 dB with Front/Back (toward 270-deg) = 20 dB.
Provides some Raw Gain on Ch2-6 and FM Band, but directed to the REAR and SWR is excessive.
Not suitable for UHF Band: poor SWR & Gain toward Diagonals.
Provides performance equal or better than Winegard YA-1713, except sidelobe nulls moved to sides and EXCELLENT F/B and F/R Ratios. |
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Lo-VHF+FM Hourglass Loop (29 Nov 2012)Lo-VHF+FM Hourglass Loop analyzed using 4nec2 after finding "best" dimensions using nikiml's Optimization Scripts.
Based on UHF Hourglass Loop posted by oneolddude in www.digitalhome.ca forum.
NO Reflector Rods (Overall 67.5-in H x 87.25-in W, using Half-inch Copper Tubing):
Raw Gain = 3.3-4.5 dBi on Ch2-6, rising to 5.5 dBi across FM Band.
Gain Loss across Ch8-13 is due to Azimuth moving to diagonals.
Excellent SWR on all channels. |
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