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 holl_ands | Home > Loop Antennas incl Folded Dipole > 
Lo-VHF Folded Dipoles
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

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)
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.

EDIT (13Jun2013): Added Ch2 (ONLY) Folded Dipole using AWG24 (e.g. 1/2-in Twinlead).
Date(s): 22 Nov 2012. Album by holl_ands. 1 - 28 of 28 Total. 7487 Visits.
Start SlideshowTo order prints and photo-products: 1. Select photos. 2. Click Order. 3. Select products.Select images and click to download to your computer 
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1
CH6 Folded Dipole - Net Gain for Different Diameters

1/2-in Copper (Type M) Tubing is good for CH6
and "adequate" for Ch5 + FM Band.
AWG12 & AWG24 good only across Ch6.


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2
CH6 Folded Dipole - SWR for Different Diameters

1/2-in Copper (Type M) Tubing is good for CH6
and "adequate" for Ch5 + FM Band.
AWG12 & AWG24 good only across Ch6.


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DOC3
CH6 Folded Dipole AWG12 - 4nec2 File

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4
Ch6 Folded Dipole 0.569-in O.D.
Ch2-FM Raw Gain
63-inches x 2.5 inch
Separation up to 3 inches with minimal impact.


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5
Ch6 Folded Dipole 0.569-in O.D.
Ch2-FM SWR (300-ohms)
63-inches x 2.5 inch


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Ch6 Folded Dipole 0.569-in O.D.
Ch2-FM Impedance
63-inches x 2.5 inch


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7
Ch6 Folded Dipole 0.569-in O.D.
Ch2-13 Raw Gain
63-inches x 2.5 inch

NOT also suitable for Hi-VHF Band.


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8
Ch6 Folded Dipole 0.569-in O.D.
Ch2-13 SWR (300-ohms)
63-inches x 2.5 inch

NOT also suitable for Hi-VHF Band.


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9
Ch6 Folded Dipole 0.569-in O.D.
Ch2-13 Impedance
63-inches x 2.5 inch

NOT also suitable for Hi-VHF Band.


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10
CH6 Folded Dipole 0.569-in O.D. - Raw Gain
63-inches x 1 inch
Separation up to 3 inches with minimal impact.


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CH6 Folded Dipole 0.569-in O.D. - SWR

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CH6 Folded Dipole 0.569-in O.D. - Impedance

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13
CH6 Folded Dipole AWG12 - Raw Gain
64.5-inches x 0.5 inch
Separation up to 1.0 inches with minimal impact.


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CH6 Folded Dipole AWG12 - SWR

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CH6 Folded Dipole AWG12 - Impedance

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16
Ch3-6 Folded Dipole 0.569-in O.D.
Ch2-6 Raw Gain
76-inches x 3 inch


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17
Ch3-6 Folded Dipole 0.569-in O.D.
Ch2-6 SWR (300-ohms), excessive on Ch2
76-inches x 3 inch


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18
Ch3-6 Folded Dipole 0.569-in O.D.
Ch2-6 Impedance
76-inches x 3 inch


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19
Ch2-6 Folded Dipole 0.569-in O.D.
Ch2-6 Raw Gain
82-inches x 3 inch


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20
Ch2-6 Folded Dipole 0.569-in O.D.
Ch2-6 SWR (300-ohms), high on Ch2 & 6
82-inches x 3 inch


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21
Ch2-6 Folded Dipole 0.569-in O.D.
Ch2-6 Impedance
82-inches x 3 inch


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22
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.


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23
CH3 Folded Dipole AWG24 [e.g. Twinlead]
Ch3 SWR (300-ohms) Under 2.0


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24
CH3 Folded Dipole AWG24 [e.g. Twinlead]
Ch3 Impedance


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25
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.


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26
CH2 Folded Dipole AWG24 [e.g. Twinlead]
Ch2 SWR (300-ohms) Under 2.2
99.25-inches x 0.5 inch


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27
CH2 Folded Dipole AWG24 [e.g. Twinlead]
Ch2-6 Impedance
99.25-inches x 0.5 inch


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28
Vertical Folded Dipole for FM Band
Slightly more Gain away from the Feedpoint.


 
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