Canadian TV, Computing and Home Theatre Forums banner

1 - 8 of 8 Posts

·
Registered
Joined
·
20 Posts
Discussion Starter #1
I feel sure this will be a dumb question, but here goes.

I have a 4bay butterfly design I've been working on for a deep fringe location. Modeling for UHF looks great with dbi gains +/- 16, low SWR, and impedance in reasonable 300 ohm tolerance. Running the VHF frequencies gives a nice gain of 7 +/-, but the general impedance is very low ~ 50 to 60 ohms.

Has anyone ever tried connecting both a balun for the UHF and hardwiring a piece of coax, at the same feed point, for the VHF then connecting these to the separate inputs in a UHF/VHF preamp?? Worth a try or waste of time??
 

·
Premium Member
Joined
·
1,114 Posts
Hello again, paxplant.

Your previous thread on the same topic for reference:
VHF / UHF integrated antenna anyone?
https://www.digitalhome.ca/forum/186-antenna-research-development/288389-vhf-uhf-integrated-antenna-anyone.html

You are using the term "4bay butterfly design" again. This is not a standard term. Do you mean 4bay bowtie design? What does your "butterfly" antenna look like?

What you want to do is not standard practice. You will have to try it to find out.

Expecting a UHF antenna to also perform well on VHF is not realistic. If you want more VHF gain than a GH10n3 with NARODS, you will need a separate VHF antenna.
https://www.digitalhome.ca/forum/186-antenna-research-development/288927-best-diy-indoor-antenna-get-ota.html

nikiml's Antenna pages - GH10n UHF/VHF-hi combo antenna
 

·
Registered
Joined
·
20 Posts
Discussion Starter #3
My humble apology Rabbit73 for my unacceptable terminology. Bowtie, and I haven't given up my pursuit... if it wouldn't be for the VHF impedance problem this thing would be a knockout!
 

·
Premium Member
Joined
·
1,114 Posts
Thank you for the clarification; I thought you had invented a new design.

Good luck with your antenna tests.
 

·
Registered
Joined
·
86 Posts
Hi Paxplant
I had the same issue with this design https://www.digitalhome.ca/forum/186-antenna-research-development/288907-hi-vhf-uhf-combo-antenna.html. It's designed to be built with 1/2" copper plumbing pipe, so its pretty easy to build, and stands up to the weather. It works well at 300ohms for the UHF side, but would work better at 75ohms on the Hi-VHF side. I had the same thought, to run it through two baluns, but assumed that it would not work. It would require something to recombine the signals, and I know that this probably will have some loss, so it will reduce the overall gain. I hope someone who understands antennas better, can give us a definitive answer. ----- I've also modeled and built a two bay folded dipole antenna, with reflectors, that gets very good results in both Hi-VHF and UHF bands. It's also built from copper tubing. See model below. It is very easy to build. Two elements are combined with a simple splitter, on equal length coax cables. It has better Hi-VHF performance, but doesn't have as much gain, in the UHF band, as your bow-tie design. It still has that steep curve, for the impedance in the Hi-VHF band, but isn't as bad as some other designs.



Code:
CM Design began with HiVHF+UHF, VEE Stick Dipole, Variable ANGLE, 4nec2 by holl_ands, 27Jul2014
CM Stacked 2 elements
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.
CM ALL MEASUREMENTS IN INCHES.
CM Char. Impedance = 300-ohm.  AGT=1.0
CM Modeled without autoseg.
CM Folding forward 45 degrees gives better UHF results and Reflectors improve Hi-VHF results
CM Two elements are combined with quality splitter.  Results is a small loss in gain.
CE
SY Scale=1.0	'Scale function
SY sc=Scale	'Scale variable
SY Rsrc=0.29	'Simulated SOURCE Wire Radius, Adjust for AGT=1.0: UHF(533)=0.32   HiVHF=0.29
SY Relem=0.3125	'Radius of Elements (1/2" copper tubing actual diameter is 5/8")
SY DipoleHeight=3.1875	'Distance between Folded Dipole Elements      3.1875
SY dh=DipoleHeight	'Distance between Folded Dipole Elements
SY gap=2.0	'Center Gap Size between Elements     3.0
SY Rlen1=36.0	'Outer Reflector length     32.0    33.88   35.0    36.0
SY Rlen2=36.0	'Inner Reflector length       32.0      35.5     35.0    36.0
SY Rback1=13.0	'Outer Reflector back from element     12.0
SY Rback2=Rback1	'Inner Reflector back from element
SY Rseperation=21.0	'Reflector Seperation betweet outer reflectors      20.0
SY Rsep=Rseperation/2	'Reflector Seperation
SY len=15.41875	'Total Length of Folded Dipole Element:     15.3875      15.41875 (14.75")
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=29.0	'Seperation of element Feed Point    29.0
SY Esep=Eseperation/2	'Seperation of element Feed Point from center
GW	1	1	gapDx*sc	-gapDy*sc	Esep*sc	gapDx*sc	gapDy*sc	Esep*sc	Rsrc	'SOURCE
GW	2	5	gapDx*sc	gapDy*sc	Esep*sc	wingDx*sc	wingDy*sc	Esep*sc	Relem
GW	3	5	gapDx*sc	-gapDy*sc	Esep*sc	wingDx*sc	-wingDy*sc	Esep*sc	Relem
GW	4	5	0	0	(Esep+dh)*sc	wingDx*sc	wingDy*sc	(Esep+dh)*sc	Relem
GW	5	5	0	0	(Esep+dh)*sc	wingDx*sc	-wingDy*sc	(Esep+dh)*sc	Relem
GW	6	1	wingDx*sc	wingDy*sc	Esep*sc	wingDx*sc	wingDy*sc	(Esep+dh)*sc	Relem
GW	7	1	wingDx*sc	-wingDy*sc	Esep*sc	wingDx*sc	-wingDy*sc	(Esep+dh)*sc	Relem
GW	21	11	-Rback1*sc	-Rlen1/2*sc	((Esep+(dh/2)+Rsep))*sc	-Rback1*sc	Rlen1/2*sc	((Esep+(dh/2)+Rsep))*sc	Relem
GW	22	11	-Rback1*sc	-Rlen1/2*sc	((Esep+(dh/2)-Rsep))*sc	-Rback1*sc	Rlen1/2*sc	((Esep+(dh/2)-Rsep))*sc	Relem
GW	23	11	-Rback2*sc	-Rlen2/2*sc	((Esep+(dh/2)))*sc	-Rback2*sc	Rlen2/2*sc	((Esep+(dh/2)))*sc	Relem
GW	31	1	gapDx*sc	-gapDy*sc	-Esep*sc	gapDx*sc	gapDy*sc	-Esep*sc	Rsrc	'SOURCE
GW	32	5	gapDx*sc	gapDy*sc	-Esep*sc	wingDx*sc	wingDy*sc	-Esep*sc	Relem
GW	33	5	gapDx*sc	-gapDy*sc	-Esep*sc	wingDx*sc	-wingDy*sc	-Esep*sc	Relem
GW	34	5	0	0	(-Esep-dh)*sc	wingDx*sc	wingDy*sc	(-Esep-dh)*sc	Relem
GW	35	5	0	0	(-Esep-dh)*sc	wingDx*sc	-wingDy*sc	(-Esep-dh)*sc	Relem
GW	36	1	wingDx*sc	wingDy*sc	-Esep*sc	wingDx*sc	wingDy*sc	(-Esep-dh)*sc	Relem
GW	37	1	wingDx*sc	-wingDy*sc	-Esep*sc	wingDx*sc	-wingDy*sc	(-Esep-dh)*sc	Relem
GW	25	11	-Rback1*sc	-Rlen1/2*sc	-((Esep+(dh/2)+Rsep))*sc	-Rback1*sc	Rlen1/2*sc	(-(Esep+(dh/2)+Rsep))*sc	Relem
GW	26	11	-Rback1*sc	-Rlen1/2*sc	-((Esep+(dh/2)-Rsep))*sc	-Rback1*sc	Rlen1/2*sc	(-(Esep+(dh/2)-Rsep))*sc	Relem
GW	27	11	-Rback2*sc	-Rlen2/2*sc	(-(Esep+(dh/2)))*sc	-Rback2*sc	Rlen2/2*sc	(-(Esep+(dh/2)))*sc	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	40	0	0	174	12
RP	0	1	73	1510	90	0	1	5	0	0
EN
I've been considering a 3 bay stacked vertically, or a 4 bay, quad arrangement, to see if it will get more gain, without any issues. That might be next week's project.
 

·
Registered
Joined
·
362 Posts
Has anyone ever tried connecting both a balun for the UHF and hardwiring a piece of coax, at the same feed point,
If you connect 2 resistances (2 impedances) with Z1=300 and Z2=75 in parallel - you will get total impedance as (300*75)/(300+75)= 60 Ohm (combined resistance is always less than any of two R in parallel)

60/75=80% of current and power (VHF or UHF doesn't matter) will flow into lesser resistance (75)
60/300=20% of current and power (VHF or UHF doesn't matter) will flow into greater resistance (300)

Second, you can not connect 75 Ohm antenna with symmetrical (differential, balanced) output (any kind of dipole or loop antenna) to unbalanced transmission line (coax). You still need 1:1 balun
 

·
Registered
Joined
·
20 Posts
Discussion Starter #7
Thanks Yurii,
My unknown is the actual impedance seen at the coax connection points in a pre-amp with separate VHF/UHF inputs. Maybe I could use a short piece of twin wire soldered to a coax connector for the VHF side and not use a short piece of coax for that connection.
 

·
Registered
Joined
·
20 Posts
Discussion Starter #8
Nice job,
The Hoverman GH10n3 Rabbit73 mentions is one terrific antenna, but I see it as a challenging build and large. Expecting to have your cake and eating it too might be to much to ask... but ya' can't blame a guy for trying!
 
1 - 8 of 8 Posts
Top