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Discussion Starter #1 (Edited)
I've been modeling a Hi-VHF and UHF combo antenna based on a design the Yurii posted on his site. I've always got 1/2" copper scraps, so I designed around 1/2" copper plumbing pipe and joints. Gain looks pretty good in both Hi-VHF and UHF bands. SWR and impedance look OK in UHF, but are a bit high in Hi-vhf. I posted it, just to see what others think, and see if anyone has ideas to improve it. This would be a pretty easy antenna to build. Uses quite a bit of copper, so it's probably only practical if you have scrap copper around.

Code:
CM Hi-VHF and UHF antenna made from 1/2" copper tubing and soldered joints.
CM By ljhavener.
CM Based on design from Yurii Pylypenko
CM Has gains of around 7.5db across the Hi-VHF band
CM The UHF stays above 10db for most of the new US Repack band.
CM Uses a lot of copper, so you might consider other
CM build materials and methods.
CM 
CM 
CM 
CE
SY Scale=1.0
SY sc=Scale
SY Rsrc=0.091	'SOURCE Wire Radius, Adjusted for AGT=1.0:      UHF(524)=0.09     VHF(194)=0.092
SY Rquad=0.3125	'BiQuad Element Radius 1/2" copper tubing
SY Rrefl=0.3125	'Reflector Element Radius
SY Rbolt=0.125	'Bolt Radius
SY Rwing=0.125	'Wing Radius     1/4" brass rod
SY feedgap=1.0	'Wing Feedpoint Gap Size
SY fgap=4.0	'BiQuad Gap Size                       4.0
SY fg=fgap/2	'1/2 element gap
SY winglen=8.0	'wing length    8.0
SY ldlen=10	'Lower diamond element length   10.0
SY ldzdelta=ldlen*.7071	'Lower diamond height
SY ldydelta=ldzdelta+fg
SY spurwidth=1.46
SY sw=spurwidth/2
SY spurhigh=6.186206
SY sh=spurhigh
SY uddelta=ldydelta-sw
SY udlen=uddelta*1.4142
SY udh=ldzdelta+uddelta
SY shz=sh+udh
SY r0length=30.0
SY r1length=30.0
SY r2length=48.0	'47.71
SY r3length=30.0
SY r0len=r0length/2
SY r1zdelta=ldzdelta
SY r1z=ldzdelta
SY r1len=r1length/2
SY r2zdelta=uddelta
SY r2z=r1z+r2zdelta
SY r2len=r2length/2
SY r3zdelta=sh
SY r3z=r2z+r3zdelta
SY r3len=r3length/2
SY rdback=15.0	'distance back to reflector          15.0
SY rdb=rdback
GW	1	5	rdb*sc	fg*sc	0*sc	rdb*sc	ldydelta*sc	ldzdelta*sc	Rquad
GW	2	5	rdb*sc	ldydelta*sc	ldzdelta*sc	rdb*sc	sw*sc	udh*sc	Rquad
GW	3	3	rdb*sc	sw*sc	udh*sc	rdb*sc	sw*sc	shz*sc	Rquad
GW	20	5	0	0	r1z*sc	0	r1len*sc	r1z*sc	Rrefl
GW	21	5	0	0	r2z*sc	0	r2len*sc	r2z*sc	Rrefl
GW	23	3	0	r1len*sc	0	0	r1len*sc	r1z*sc	Rrefl
GX	999	010
GW	100	1	rdb*sc	sw*sc	shz*sc	rdb*sc	-sw*sc	shz*sc	Rquad
GW	101	3	0	0	r2z*sc	0	0	r1z*sc	Rrefl
GX	999	001
GW	200	1	rdb*sc	fg*sc	0*sc	rdb*sc	feedgap/2*sc	0*sc	Rwing
GW	201	1	rdb*sc	-fg*sc	0*sc	rdb*sc	-feedgap/2*sc	0*sc	Rwing
GW	202	5	rdb*sc	fg*sc	0*sc	rdb*sc	(fg+winglen)*sc	0*sc	Rwing
GW	203	5	rdb*sc	-fg*sc	0*sc	rdb*sc	-(fg+winglen)*sc	0*sc	Rwing
GW	300	5	0	0	0*sc	0	r0len*sc	0*sc	Rrefl
GW	301	5	0	0	0*sc	0	-r0len*sc	0*sc	Rrefl
GW	900	1	rdb*sc	-feedgap/2*sc	0*sc	rdb*sc	feedgap/2*sc	0*sc	Rsrc
GS	0	0	0.0254
GE	0
LD	5	0	0	0	58000000	'Copper Elements
GN	-1
EK
EX	0	900	1	0	1	0	0
FR	0	40	0	0	174	12
RP	0	1	73	1510	90	0	1	5	0	0
EN
Antenna looks works OK at 300ohms, but the Hi-vhf end might would work better at 75ohms.

I tried to set the model up so that it's easy to change parameters, without effecting to much of the rest of the model.

Go ahead and play with it, and see what you can do.
 

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Discussion Starter #3
Antenna is a Biquad with unusual spur coming off the top and bottom diamond. Antenna element is about 20" wide and 40" tall. It sits 15" in front of an array of reflector elements. Reflector array is 30" high and 48" wide. I've added some model picts below.







Reflector array was designed to be built with common copper plumbing pipe and fittings. Could also be built with only the horizontal elements, held by PVC frame. I did get a slight improvement in the swr at 174mhz when I added the vertical elements.

Let me know if you have any questions.
 

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Discussion Starter #5
Hi rabbit73
Yes, that is the antenna, on Yurii's site. When I saw it, it looked like another good candidate, for my pile of copper plumbing pipes. I live in rural Colorado and we only have two UHF OTA channels, so this antenna really isn't much use locally. I've got friends in Colorado Springs, and they have a good selection of stations, in the Hi-VHF and UHF bands. I'll make one of these antennas, and try it in Colorado Springs, once we get past this covid-19 lockdown. Looks like covid-19 has us staying at home, for the next month. Hopefully this get some interest, and folks might have some ideas, on improving it, before I build and test it. I'd love to see if the SWR could be reduced at 174mhz and it will be interesting to see if anyone can get any more gain in Hi-VHF.

I've got much smaller versions of a very similar antenna, that works great for UHF, and is easy to build from scrap plumbing copper, if anyone is interested. This one is about 16" x 16" x 6" and has close to 10db gain across the UHF band. (see picture below)



Lawrence
 

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Discussion Starter #7
Hi Bouval
Antenna in the picture is a UHF only version. It is attached to the reflector at a null point, and is very close to 300ohm. I've modeled it with and without the connecting bolts, and it does not make any difference at all. I haven't checked the Hi-VHF/UHF version to see if it has any null points. Build from 1/2" copper plumbing pipe does make it heavy, but it's advantage is the availability of material, and ease of construction. This is a very easy antenna for anyone who has scrap copper pipe and knows how to solder copper. I have not built one of UHF/Hi-VHF version shown in the model yet. It will have the disadvantage of being heavy, but will also be easy to build. Design could be built from other materials, depending on what you have access to and can work with. One of the problems, with the UHF/Hi-VHF version, is that it's impedance is lower than 300ohms, especially in the Hi-VHF band. I'm hoping that someone might be able to improve on that. One option would be to use a custom 2:1 balum and run it at 150ohm. That improves the SWR in the Hi-VHF band, but makes it worse in the UHF band. SWR gets pretty high, in the UHF band, if you run it at 75ohm. I posted this, just to see what ideas others had, to improve the design. Maybe someone has a suggestion, that will improve it. Primarily it needs something that will improve the impedance balance between Hi-VHF and UHF. Maybe someone else is stuck at home, due to Covid-19 like I am, and has some time to play with the design.

Lawrence
 

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Discussion Starter #8
Second generation

I've done some more work on this antenna. I've been able to improve the impedance match and SWR across most of the HI-VHF and UHF(repack) band. I redesigned the reflectors, with separate elements, probably held in place, with a pvc framework. I simplified it, by using equal length reflectors. You can make minor improvements, by using different length reflectors, if you want to. This design gives more flexibility in your choice of materials. Design does seem to prefer thick elements. It can be built with thinner elements, without affecting the antenna performance that much. I'm still hoping that someone will come up with a way to lower SWR, primarily in the hI-VHF band. Many of my dimensions end in .1875 or .6875, because this allows the length of cut tubing to come out at 1/2" or 1" measurements. The difference is made up by the soldered elbow or T. This makes the antenna easier to build.

Code:
CM Hi-VHF and UHF antenna made from 1/2" copper tubing and soldered joints.
CM Second Generation
CM By ljhavener.
CM Based on design from Yurii Pylypenko
CM Has gains of around 7.5db across the Hi-VHF band
CM The UHF stays above 10db for most of the new US Repack band.
CM Uses a lot of copper, so you might consider other
CM build materials and methods.
CM 
CM 
CE
SY Scale=1.0
SY sc=Scale
SY Rsrc=0.081	'SOURCE Wire Radius, Adjusted for AGT=1.0:      UHF(533)=0.091     VHF(194)=0.071
SY Rquad=0.3125	'BiQuad Element Radius 1/2" copper tubing
SY Rrefl=0.3125	'Reflector Element Radius
SY Rbolt=0.125	'Bolt Radius
SY Rwing=0.125	'Wing Radius     1/4" brass rod
SY feedgap=1.0	'Wing Feedpoint Gap Size
SY fgap=3.81	'BiQuad Gap Size                       3.81
SY fg=fgap/2	'1/2 element gap
SY winglen=14.0	'wing length    14.0
SY ldlen=9.6875	'Lower diamond element length   9.6875
SY ldzdelta=ldlen*.7071	'Lower diamond height
SY ldydelta=ldzdelta+fg
SY spurwidth=1.6875	'1.6875
SY sw=spurwidth/2
SY spurhigh=6.1875	'6.1875
SY sh=spurhigh
SY uddelta=ldydelta-sw
SY udlen=uddelta*1.4142
SY udh=ldzdelta+uddelta
SY shz=sh+udh
SY r0length=38.0	'38.0
SY r1length=38.0	'38.0
SY r2length=38.0	'38.0
SY r3length=30.0	'30.0         not used
SY r0len=r0length/2
SY r1zdelta=ldzdelta
SY r1z=ldzdelta
SY r1len=r1length/2
SY r2zdelta=uddelta
SY r2z=r1z+r2zdelta
SY r2len=r2length/2
SY r3zdelta=sh	'not used
SY r3z=r2z+r3zdelta	'not used
SY r3len=r3length/2	'not used
SY rdback=14.75	'distance back to reflector          14.75
SY rdb=rdback
GW	1	5	rdb*sc	fg*sc	0*sc	rdb*sc	ldydelta*sc	ldzdelta*sc	Rquad
GW	2	5	rdb*sc	ldydelta*sc	ldzdelta*sc	rdb*sc	sw*sc	udh*sc	Rquad
GW	3	3	rdb*sc	sw*sc	udh*sc	rdb*sc	sw*sc	shz*sc	Rquad
GW	20	7	0	0	r1z*sc	0	r1len*sc	r1z*sc	Rrefl
GW	21	7	0	0	r2z*sc	0	r2len*sc	r2z*sc	Rrefl
GX	999	010
GW	100	1	rdb*sc	sw*sc	shz*sc	rdb*sc	-sw*sc	shz*sc	Rquad
GX	999	001
GW	200	1	rdb*sc	fg*sc	0*sc	rdb*sc	feedgap/2*sc	0*sc	Rwing
GW	201	1	rdb*sc	-fg*sc	0*sc	rdb*sc	-feedgap/2*sc	0*sc	Rwing
GW	202	5	rdb*sc	fg*sc	0*sc	rdb*sc	(fg+winglen)*sc	0*sc	Rwing
GW	203	5	rdb*sc	-fg*sc	0*sc	rdb*sc	-(fg+winglen)*sc	0*sc	Rwing
GW	300	13	0	0	0*sc	0	r0len*sc	0*sc	Rrefl
GW	301	13	0	0	0*sc	0	-r0len*sc	0*sc	Rrefl
GW	900	1	rdb*sc	-feedgap/2*sc	0*sc	rdb*sc	feedgap/2*sc	0*sc	Rsrc
GS	0	0	0.0254
GE	0
LD	5	0	0	0	58000000	'Copper Elements
GN	-1
EK
EX	0	900	1	0	1	0	0
FR	0	40	0	0	174	12
RP	0	1	73	1510	90	0	1	5	0	0
EN
At least this gives us something to do, while were stuck at home.
 
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