Stacking Folded Dipole for OTA - wiring suggestions - Canadian TV, Computing and Home Theatre Forums

 
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post #1 of 3 (permalink) Old 2019-04-21, 10:53 PM Thread Starter
 
Join Date: Jan 2018
Location: Salida, CO
Posts: 44
Stacking Folded Dipole for OTA - wiring suggestions

I was looking for a simple DIY antenna to carry with me when I go camping. I started with a forward swept folded Dipole from Hollands site. I have access to plumbing tubes, so I designed it around 1/2" plumbing pipe and fittings. Went with a 22.5 degree sweep, on each side. This allows me to use a 45 degree elbow in the middle and 90 degree elbows to form the sides. This gave me pretty good results. I was looking for better gain, so I thought about stacking 2 elements. I went with triple folded dipole because of the 600ohm impedance. When they are wired in parallel, I should be able to use a 300ohm to 75ohm balun. I'm looking for some help in designing the wiring harness. I'd like anyone's suggestions for design as well as cheap and easy to find material. I'd like to make it so that it can be easily taken apart, so that the antennas can be compact for storage. I'll build a pvc framework to hold antenna when in use. Should each section of the wiring harness be designed for 300ohm or 600ohm.

I've also modeled this design with a 28.5" reflector spaced 13.375" behind each element, and it helps with the gain on UHF and Hi-VHF.

Code:
CM Design began with HiVHF+UHF, VEE Stick Dipole, Variable ANGLE, 4nec2 by holl_ands, 27Jul2014
CM Stacked 2 elements
CM Triple folded Dipole to get 600ohm impedance
CM All elements 5/8-in Copper (1/2" plumbing tubing and joints) 
CM Folded forward 22.5 degrees (use 45 degree elbow)
CM Sides are 90 degree elbows and tee.
CM ALL MEASUREMENTS IN INCHES.
CM Char. Impedance = 600-ohm.  AGT=1.0
CM Modeled without autoseg.
CM 
CE
SY Rsrc=0.35	'Simulated SOURCE Wire Radius, Adjust for AGT=1.0: UHF(584)=0.37,   HiVHF=0.33
SY Relem=0.3125	'Radius of Elements (5/8-in)
SY DipoleHeight=1.6875	'Distance between Folded Dipole Elements
SY dh=DipoleHeight	'Distance between Folded Dipole Elements
SY gap=3.0	'Center Gap Size between Elements
SY len=14.1875	'20, 40    Total Length of Folded Dipole Element:
SY Angle=45	'0, 60    Swept Forward Angle away from Y-Axis (For Straight Dipole set Angle=0.0):
SY ang2=Angle/2	'0, 60    Swept Forward Angle away from Y-Axis (For Straight Dipole set Angle=0.0):
SY wingDx=len*sin(ang2)	'Wing end location X axis
SY wingDy=len*cos(ang2)	'Wing end location Y axis
SY gapDy=gap/2	'Gap end location Y axis
SY gapDx=gapDy*tan(ang2)	'Gap end location X axis
SY Eseperation=32.0	'Seperation of element Feed Point
SY Esep=Eseperation/2	'Seperation of element Feed Point
GW	1	1	gapDx	-gapDy	Esep	gapDx	gapDy	Esep	Rsrc	'SOURCE
GW	2	11	gapDx	gapDy	Esep	wingDx	wingDy	Esep	Relem
GW	3	11	gapDx	-gapDy	Esep	wingDx	-wingDy	Esep	Relem
GW	4	13	0	0	Esep+dh	wingDx	wingDy	Esep+dh	Relem
GW	5	13	0	0	Esep+dh	wingDx	-wingDy	Esep+dh	Relem
GW	6	1	wingDx	wingDy	Esep	wingDx	wingDy	Esep+dh	Relem
GW	7	1	wingDx	-wingDy	Esep	wingDx	-wingDy	Esep+dh	Relem
GW	8	1	wingDx	wingDy	Esep+dh	wingDx	wingDy	Esep+dh+dh	Relem
GW	9	1	wingDx	-wingDy	Esep+dh	wingDx	-wingDy	Esep+dh+dh	Relem
GW	10	13	0	0	Esep+dh+dh	wingDx	wingDy	Esep+dh+dh	Relem
GW	11	13	0	0	Esep+dh+dh	wingDx	-wingDy	Esep+dh+dh	Relem
GW	31	1	gapDx	-gapDy	-Esep	gapDx	gapDy	-Esep	Rsrc	'SOURCE
GW	32	11	gapDx	gapDy	-Esep	wingDx	wingDy	-Esep	Relem
GW	33	11	gapDx	-gapDy	-Esep	wingDx	-wingDy	-Esep	Relem
GW	34	13	0	0	-Esep-dh	wingDx	wingDy	-Esep-dh	Relem
GW	35	13	0	0	-Esep-dh	wingDx	-wingDy	-Esep-dh	Relem
GW	36	1	wingDx	wingDy	-Esep	wingDx	wingDy	-Esep-dh	Relem
GW	37	1	wingDx	-wingDy	-Esep	wingDx	-wingDy	-Esep-dh	Relem
GW	38	1	wingDx	wingDy	-Esep-dh	wingDx	wingDy	-Esep-dh-dh	Relem
GW	39	1	wingDx	-wingDy	-Esep-dh	wingDx	-wingDy	-Esep-dh-dh	Relem
GW	40	13	0	0	-Esep-dh-dh	wingDx	wingDy	-Esep-dh-dh	Relem
GW	41	13	0	0	-Esep-dh-dh	wingDx	-wingDy	-Esep-dh-dh	Relem
GS	0	0	0.0254
GE	0
LD	5	0	0	0	58000000	'Copper Elements
GN	-1
EK
EX	0	1	1	0	1	0	0
EX	0	31	1	0	1	0	0
FR	0	45	0	0	174	12
RP	0	1	73	1510	90	0	1	5	0	0
EN
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post #2 of 3 (permalink) Old 2019-04-22, 02:31 AM
 
Join Date: May 2017
Posts: 315
Quote:
Should each section of the wiring harness be designed for 300ohm or 600ohm.
600 Ohm is "out of range" for symmetrical wire. It has so big gap (74 times wire diameter), that it has enormous magnetic field (you cannot guarantee free space around that huge area) and higher order propagation modes.

Historically, 2x 600 Ohm antennas were connected using 300 Ohm line with length Lambda/2. This is narrowband (single channel) aproach.

Viable symmetric line impedance ranges from 100 to 450 Ohm. <100 and >450 it become ridiculously tight or wide

Last edited by Yurii Pylypenko; 2019-04-22 at 05:53 AM.
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post #3 of 3 (permalink) Old 2019-05-10, 02:10 AM Thread Starter
 
Join Date: Jan 2018
Location: Salida, CO
Posts: 44
Further refinements of design

I've spent some time refining this design and testing it's potential. I found that folding the elements forward 90 degrees, instead of 45 degrees, adds gain in the UHF band without much loss in the Hi-VHF. Reflectors add gain in the Hi-VHF band as well as some gain in the UHF band. It may not be the most practical design, but I'm getting very good Hi-VHF and UHF performance out of the design below. It uses 3 fairly long reflectors behind each element. You get pretty good results with one two or three reflectors between 28-30" as well. Changing the reflectors to smaller(1/4") material loses just a bit of gain, while using less material.
I'm still looking for ideas for a wiring harness to join the two elements. Will old fashioned 300ohm flat wire connecting to a centrally mounted 4to1 balun work well? Does the length of the wiring harness affect the results, as long as both segments are the same length? Does anyone have any experience with this kind of setup? Would I get better results with two baluns and a central mounted combiner of some sort?

I see this as a design that can be easily taken apart and stored in a pretty small area, when I'm car camping. It's pretty modular, with good pretty good results from any combination of just one element, two elements, two elements with just one reflector, or the entire setup as modeled below.

Thanks for any help.

Code:
CM Design began with HiVHF+UHF, VEE Stick Dipole, Variable ANGLE, 4nec2 by holl_ands, 27Jul2014
CM Stacked 2 elements
CM Triple folded Dipole to get 600ohm impedance
CM All elements 5/8-in Copper (1/2" plumbing tubing and joints) 
CM Folded forward 45 degrees (use 90 degree elbow)
CM Sides are 90 degree elbows and tee.
CM ALL MEASUREMENTS IN INCHES.
CM Char. Impedance = 600-ohm.  AGT=1.0
CM Modeled without autoseg.
CM Folding forward 45 degrees gives better UHF results and Reflectors improve Hi-VHF results
CE
SY Rsrc=0.35	'Simulated SOURCE Wire Radius, Adjust for AGT=1.0: UHF(584)=0.37,   HiVHF=0.33
SY Relem=0.3125	'Radius of Elements (1/2" copper tubing actual diameter is 5/8")
SY DipoleHeight=1.6875	'Distance between Folded Dipole Elements
SY dh=DipoleHeight	'Distance between Folded Dipole Elements
SY gap=3.0	'Center Gap Size between Elements
SY Rlen1=37.6875	'Outer Reflector length
SY Rlen2=71.6875	'Inner Reflector length
SY Rback1=12.0	'Outer Reflector back from element
SY Rback2=12.0	'Inner Reflector back from element
SY Rseperation=20.0	'Reflector Seperation betweet outer reflectors
SY Rsep=Rseperation/2	'Reflector Seperation
SY len=14.6875	'Total Length of Folded Dipole Element:
SY Angle=90	'Sweep Angle between element legs (For Straight Dipole set Angle=0.0):
SY ang2=Angle/2	'Swept Forward Angle away from Y-Axis (For Straight Dipole set Angle=0.0):
SY wingDx=len*sin(ang2)	'Wing end location X axis
SY wingDy=len*cos(ang2)	'Wing end location Y axis
SY gapDy=gap/2	'Gap end location Y axis
SY gapDx=gapDy*tan(ang2)	'Gap end location X axis
SY Eseperation=32.0	'Seperation of element Feed Point
SY Esep=Eseperation/2	'Seperation of element Feed Point from center
GW	1	1	gapDx	-gapDy	Esep	gapDx	gapDy	Esep	Rsrc	'SOURCE
GW	2	11	gapDx	gapDy	Esep	wingDx	wingDy	Esep	Relem
GW	3	11	gapDx	-gapDy	Esep	wingDx	-wingDy	Esep	Relem
GW	4	13	0	0	Esep+dh	wingDx	wingDy	Esep+dh	Relem
GW	5	13	0	0	Esep+dh	wingDx	-wingDy	Esep+dh	Relem
GW	6	1	wingDx	wingDy	Esep	wingDx	wingDy	Esep+dh	Relem
GW	7	1	wingDx	-wingDy	Esep	wingDx	-wingDy	Esep+dh	Relem
GW	8	1	wingDx	wingDy	Esep+dh	wingDx	wingDy	Esep+dh+dh	Relem
GW	9	1	wingDx	-wingDy	Esep+dh	wingDx	-wingDy	Esep+dh+dh	Relem
GW	10	13	0	0	Esep+dh+dh	wingDx	wingDy	Esep+dh+dh	Relem
GW	11	13	0	0	Esep+dh+dh	wingDx	-wingDy	Esep+dh+dh	Relem
GW	21	19	-Rback1	-Rlen1/2	(Esep+dh+Rsep)	-Rback1	Rlen1/2	(Esep+dh+Rsep)	Relem
GW	22	19	-Rback1	-Rlen1/2	(Esep+dh-Rsep)	-Rback1	Rlen1/2	(Esep+dh-Rsep)	Relem
GW	23	19	-Rback2	-Rlen2/2	(Esep+dh)	-Rback2	Rlen2/2	(Esep+dh)	Relem
GW	31	1	gapDx	-gapDy	-Esep	gapDx	gapDy	-Esep	Rsrc	'SOURCE
GW	32	11	gapDx	gapDy	-Esep	wingDx	wingDy	-Esep	Relem
GW	33	11	gapDx	-gapDy	-Esep	wingDx	-wingDy	-Esep	Relem
GW	34	13	0	0	-Esep-dh	wingDx	wingDy	-Esep-dh	Relem
GW	35	13	0	0	-Esep-dh	wingDx	-wingDy	-Esep-dh	Relem
GW	36	1	wingDx	wingDy	-Esep	wingDx	wingDy	-Esep-dh	Relem
GW	37	1	wingDx	-wingDy	-Esep	wingDx	-wingDy	-Esep-dh	Relem
GW	38	1	wingDx	wingDy	-Esep-dh	wingDx	wingDy	-Esep-dh-dh	Relem
GW	39	1	wingDx	-wingDy	-Esep-dh	wingDx	-wingDy	-Esep-dh-dh	Relem
GW	40	13	0	0	-Esep-dh-dh	wingDx	wingDy	-Esep-dh-dh	Relem
GW	41	13	0	0	-Esep-dh-dh	wingDx	-wingDy	-Esep-dh-dh	Relem
GW	25	19	-Rback1	-Rlen1/2	-(Esep+dh+Rsep)	-Rback1	Rlen1/2	-(Esep+dh+Rsep)	Relem
GW	26	19	-Rback1	-Rlen1/2	-(Esep+dh-Rsep)	-Rback1	Rlen1/2	-(Esep+dh-Rsep)	Relem
GW	27	19	-Rback2	-Rlen2/2	-(Esep+dh)	-Rback2	Rlen2/2	-(Esep+dh)	Relem
GS	0	0	0.0254
GE	0
LD	5	0	0	0	58000000	'Copper Elements
GN	-1
EK
EX	0	1	1	0	1	0	0
EX	0	31	1	0	1	0	0
FR	0	45	0	0	174	12
RP	0	1	73	1510	90	0	1	5	0	0
EN
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