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.
Note that even HICT (Half-Inch Copper Tubing) is NOT FAT ENOUGH to provide "acceptable" SWR [i.e. Under 2.7 so Mis-match Loss under 1.0 dB] for ENTIRE Lo-VHF Band (Ch2-6), but is just slightly over SWR = 2.7 for Ch3-6. And small, AWG24 wire size [such as is used in 300-ohm Twin-lead] was only suitable for SINGLE CHANNEL Antennas.
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) 63.4 x 2.0 inch - 0.25-in O.D. Copper Wire (Ch6, but SWR high for CH5 & FM Band). 64.0 x 2.0 inch - AWG10 Copper Wire (Ch6, but SWR too high for CH5 & FM Band). 64.0 x 3.0 inch - AWG12 Copper Wire (Ch6, but SWR too high for CH5 & 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) 99.24 x 0.5 inch - AWG24 Copper Wire (Ch2 ONLY) [Reduce Length by Velocity Factor if using 1/2-inch Twinlead.]
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.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.
enlarge 157KB, 1152x692 13 Ch3-6 Folded Dipole 0.569-in O.D. Ch2-6 Raw Gain 76-inches x 3 inch
enlarge 207KB, 1152x692 14 Ch3-6 Folded Dipole 0.569-in O.D. Ch2-6 SWR (300-ohms), excessive on Ch2 76-inches x 3 inch
enlarge 241KB, 1152x692 15 Ch3-6 Folded Dipole 0.569-in O.D. Ch2-6 Impedance 76-inches x 3 inch
enlarge 158KB, 1152x692 16 Ch2-6 Folded Dipole 0.569-in O.D. Ch2-6 Raw Gain 82-inches x 3 inch
enlarge 203KB, 1152x692 17 Ch2-6 Folded Dipole 0.569-in O.D. Ch2-6 SWR (300-ohms), high on Ch2 & 6 82-inches x 3 inch
enlarge 249KB, 1152x692 18 Ch2-6 Folded Dipole 0.569-in O.D. Ch2-6 Impedance 82-inches x 3 inch
enlarge 188KB, 1152x701 19 CH3 Folded Dipole AWG24 [e.g. Twinlead] Ch3 Raw Gain = 2.1 to 2.2 dBi 89.75-inches x 0.5 inch Separation up to 1.0 inches with minimal impact.
enlarge 169KB, 1152x678 22 CH2 Folded Dipole AWG24 [e.g. Twinlead] Ch2-6 Raw Gain = 2.1 to 2.8 dBi 99.25-inches x 0.5 inch Separation up to 1.0 inches with minimal impact.
enlarge 202KB, 1152x678 23 CH2 Folded Dipole AWG24 [e.g. Twinlead] Ch2 SWR (300-ohms) Under 2.2 99.25-inches x 0.5 inch
enlarge 247KB, 1152x678 24 CH2 Folded Dipole AWG24 [e.g. Twinlead] Ch2-6 Impedance 99.25-inches x 0.5 inch
enlarge 43KB, 1024x691 25 Ch6 Folded Dipole AWG10 3D View
enlarge 91KB, 1152x261 26 Ch6 Folded Dipole AWG10 Front View 64.0-inches x 2.0 inch
enlarge 27KB, 791x1024 27 CH6 Folded Dipole AWG10 4nec2 text File includes Dimensions
enlarge 178KB, 1152x664 28 Ch6 Folded Dipole AWG10 Ch6 (82-88 MHz) Raw Gain = 2.1 to 2.1 dBi
enlarge 207KB, 1152x664 29 Ch6 Folded Dipole AWG10 Ch6 (82-88 MHz) SWR (300-ohms) = 1.4 to 1.1 to 1.4