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
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 Lo-VHF Folded Dipole album.
Date(s): 15 July 2009. Album by holl_ands. 1 - 41 of 41 Total. 30694 Visits.
enlarge 0KB, 1024x748 1 Hi-VHF Folded Dipole - Net Gain for Different Diameters
1/2-in Copper Tube with four Elbows looks good. Total cost about $10 incl. a cheap Balun.
enlarge 0KB, 1024x742 2 Hi-VHF Folded Dipole - SWR for Different Diameters
Length adjusted for equal SWR at freq extremes. [I wasn't as finicky with some of them...]
enlarge 0KB, 771x1024 3 Hi-VHF Folded Dipole - Outdoor on Pergola Ch7/9 barely OK 70-miles from Mt Wilson (L.A.)
Didn't expect Ch11/13 due to Ch12 (2.7 miles) blocking adjacent channel reception.
enlarge 0KB, 651x1024 4 Clean all connections down to bare metal. Thin coat of Plumbers Soldering Flux (round tin).
Seal Brass screw inside Cap pieces. Torch and Plumbers Tin/Silver Solder.
enlarge 0KB, 669x1024 5 Brazing end pieces
Only other brazing job (ever) was last week to fix a corroded valve on the water heater. "I would just like to point out that ..." View Comments...
enlarge 0KB, 1024x565 6 Brazing Cap pieces.
Fluxed everything & reheat for final seal while wiping off excess solder with wet rag.
Hi-VHF (Ch7-13) full-band coverage size is 27.5-in x 2.0-in Center-to-Center
Ch5/6/FM size is 63-in x 2-in Center-to-Center.
enlarge 0KB, 1024x819 7 Hi-VHF Folded Dipole - Raw Gain One Inch O.D. Copper Tubing 27-inches x 2 inch
enlarge 0KB, 1024x819 8 Hi-VHF Folded Dipole - SWR One Inch O.D. Copper Tubing 27-inches x 2 inch
enlarge 0KB, 1024x819 9 Hi-VHF Folded Dipole - Impedance One Inch O.D. Copper Tubing 27-inches x 2 inch
enlarge 0KB, 1024x819 10 Hi-VHF Folded Dipole - Raw Gain 0.569-in O.D. Copper Tubing 27.5-inches x 2 inch
enlarge 0KB, 1024x819 11 Hi-VHF Folded Dipole - SWR 0.569-in O.D. Copper Tubing 27.5-inches x 2 inch
enlarge 0KB, 1024x819 12 Hi-VHF Folded Dipole - Impedance 0.569-in O.D. Copper Tubing 27.5-inches x 2 inch
enlarge 0KB, 1024x819 13 Hi-VHF Folded Dipole - Raw Gain 5/16-in O.D. Copper Tubing 28.0-inches x 1 inch
enlarge 0KB, 1024x819 14 Hi-VHF Folded Dipole - SWR 5/16-in O.D. Copper Tubing 28.0-inches x 1 inch
enlarge 0KB, 1024x819 15 Hi-VHF Folded Dipole - Impedance 5/16-in O.D. Copper Tubing 28.0-inches x 1 inch
enlarge 162KB, 1152x692 16 Hi-VHF Folded Dipole - Raw Gain 5/16-in O.D. Copper Tubing Ch2-13 Raw Gain
enlarge 236KB, 1152x692 17 Hi-VHF Folded Dipole - Raw Gain 5/16-in O.D. Copper Tubing Ch2-13 SWR (300-ohms)
enlarge 248KB, 1152x692 18 Hi-VHF Folded Dipole - Raw Gain 5/16-in O.D. Copper Tubing Ch2-13 Impedance
enlarge 0KB, 1024x819 19 Hi-VHF Folded Dipole - Raw Gain Quarter Inch Copper Tubing 28-inches x 1 inch
enlarge 0KB, 1024x819 20 Hi-VHF Folded Dipole - SWR Quarter Inch Copper Tubing 28-inches x 1 inch
enlarge 0KB, 1024x819 21 Hi-VHF Folded Dipole - Impedance Quarter Inch Copper Tubing 28-inches x 1 inch
enlarge 140KB, 1024x790 22 Hi-VHF Folded Dipole: 3D Total Gain Pattern at 198 MHz Quarter Inch Copper Tubing 28-inches x 1 inch
enlarge 137KB, 1024x794 23 Hi-VHF Folded Dipole: 3D Horiz. Gain Pattern at 198 MHz Quarter Inch Copper Tubing 28-inches x 1 inch
enlarge 138KB, 1024x790 24 Hi-VHF Folded Dipole: 3D Vert. Gain Pattern at 198 MHz Quarter Inch Copper Tubing 28-inches x 1 inch
enlarge 0KB, 1024x819 25 Hi-VHF Folded Dipole - Raw Gain AWG12 Copper Wire 28.25-inches x 1 inch
enlarge 0KB, 1024x819 26 Hi-VHF Folded Dipole - SWR AWG12 Copper Wire 28.25-inches x 1 inch
enlarge 0KB, 1024x819 27 Hi-VHF Folded Dipole - Impedance AWG12 Copper Wire 28.25-inches x 1 inch
enlarge 0KB, 1024x819 28 Hi-VHF Folded Dipole - Raw Gain AWG24 Copper Wire 28.5-inches x 1 inch
enlarge 0KB, 1024x819 29 Hi-VHF Folded Dipole - SWR AWG24 Copper Wire 28.5-inches x 1 inch
enlarge 0KB, 1024x819 30 Hi-VHF Folded Dipole - Impedance AWG24 Copper Wire 28.5-inches x 1 inch
enlarge 165KB, 1152x692 31 Hi-VHF Folded Dipole AWG24 Copper Wire Hi-VHF Raw Gain
Has anyone tried any of the fractal designs for a tv antenna, I have tried almost all of the store bought antennas including the huge ones that take two people to put up. - daniel | na, Sun, 16 Nov 2014 10:53PM
Great site! I can clear up your ideas about gap size. In practice the feed wire (any type) takes up the gap so there is NO practical difference no matter how wide it is. - Keith, Mon, 19 May 2014 7:51PM
I can use this website alot. I like to build my own antennas. Thank You very much. - Doug McAbee | none, Mon, 31 Oct 2011 5:50PM
