Most literature on inverted V antennas gives a angle range of 60-120 degrees included. I have been searching, to no avail, what the angle's affect is on the impedance of the antenna. Does anyone out there know of a graph or chart of some sort that shows the relationship between angle and impedance and where to find it?
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Inverted V angle
- Thread starter Pman62
- Start date
BJ radionut
Supporting Member and 6m addict
http://www.comportco.com/~w5alt/antennas/notes/ant-notes.php?pg=15
http://www.comportco.com/~w5alt/antennas/notes/ant-notes.php?pg=13
This info may help...reference antenna is for 40m...but info still applies...
My experience for Omni directional usage the "V" angle is best at 90-120 deg...
This seems to be the"sweet spot" where calculated length and reactance are in the 50 ohm and X=0 range...
BUT every location and set-up varies, as ground losses and height plus proximity to other objects are always factors.
All the Best
Gary
http://www.comportco.com/~w5alt/antennas/notes/ant-notes.php?pg=13
This info may help...reference antenna is for 40m...but info still applies...
My experience for Omni directional usage the "V" angle is best at 90-120 deg...
This seems to be the"sweet spot" where calculated length and reactance are in the 50 ohm and X=0 range...
BUT every location and set-up varies, as ground losses and height plus proximity to other objects are always factors.
All the Best
Gary
I have never heard an angle as low as 60 degrees but you want the angle at least 90 degrees. The reason is not so much as impedance matching but rather signal cancellation. At less than 90 degrees the radiation from both sides tends to cancel in the far field and results in poorer performance.
I'm assuming you are not planning on just building a bent dipole here.
Below is my old Horizontal model of the Maco 2 element V Quad, to specs, shows a great match, with modest gain.
This model has the radiator wires angled at 45* degrees, so the overall span is 90* degrees. That said however, all the elements are longer than usual relative to what we tend to think for a typical 1/4 wave element length at 27.205 MHz. I suspect that may have something to do with this Quad having only 3 sides instead of 4.
Eznec does not allow the use of taper and I'm not too sure about the results I got using #12 wire attached to the aluminum parts of the radiator, because that too is using taper. That said however, the model looks reasonable to me.
The PDF file below shows the dimensions in inches for each wire on the driven element. The short wires #5 & #7 were used due to limitations in modeling. The tips of the Maco VQ are bent to connect to the top wire...the primary radiating element. I cannot model such bends, so I use these additional short straight wires to simulate the curved portions. Wire diameters must also be considered and the real antenna uses tapered element and wire at the top.
The model also shows 12.18 dbi gain with -10 reflection and that is off a bit from Maco's published performance results.
This might help with some dimensions, but there should be a specific antenna calculator some where on the Internet I would guess.
Good luck and keep us posted on your progress.
Below is my old Horizontal model of the Maco 2 element V Quad, to specs, shows a great match, with modest gain.
This model has the radiator wires angled at 45* degrees, so the overall span is 90* degrees. That said however, all the elements are longer than usual relative to what we tend to think for a typical 1/4 wave element length at 27.205 MHz. I suspect that may have something to do with this Quad having only 3 sides instead of 4.
Eznec does not allow the use of taper and I'm not too sure about the results I got using #12 wire attached to the aluminum parts of the radiator, because that too is using taper. That said however, the model looks reasonable to me.
The PDF file below shows the dimensions in inches for each wire on the driven element. The short wires #5 & #7 were used due to limitations in modeling. The tips of the Maco VQ are bent to connect to the top wire...the primary radiating element. I cannot model such bends, so I use these additional short straight wires to simulate the curved portions. Wire diameters must also be considered and the real antenna uses tapered element and wire at the top.
The model also shows 12.18 dbi gain with -10 reflection and that is off a bit from Maco's published performance results.
This might help with some dimensions, but there should be a specific antenna calculator some where on the Internet I would guess.
Good luck and keep us posted on your progress.
The reason I asked this is I have been playing around with a inverted V dipole. I made a very simple temporary (no BALUN) to experiment with. While tuning, I realized (same as I read) that the wires are relatively shorter than one would expect for 27.185 mHz (middle of the band.) At one point, I had SWR of 1.4 on channel 40 and 1.8 on channel one, so I went to shorten it up a little more, but when I hoisted it back up I had around 2.2 across all the channels. I believe I might not have had my angle exactly the same as I added another mast pole and just "eyeballed" the angle. I wound a 1:1 BALUN tonight as I was definitely getting radiation from my coax. The radiation was bad enough to make swr measurements a little tricky as my swr meter doubles as a field strength meter (old Radio Shack cheapy) and every time my hand got close to the port for the field strength antenna it made the meter jump up 
.
.
For my inverted V I started here http://www.sotamaps.org/extras.php and tuned them up. I have 3 inverted V's for different mast that I use for SOTA.
http://www.hamuniverse.com/dipivcal.html
http://www.hamuniverse.com/wb4yjtdipolepatterns.html
Length of dipole legs,
angle of element legs
height above ground.
All the above figure in to the vswr measurement.
Length and angle of the dipole legs can be correct and still have a less than optimum impedance due to height above ground.
http://www.hamuniverse.com/wb4yjtdipolepatterns.html
Length of dipole legs,
angle of element legs
height above ground.
All the above figure in to the vswr measurement.
Length and angle of the dipole legs can be correct and still have a less than optimum impedance due to height above ground.
I think I have a good working inverted v now. I added my home brew BALUN, have the antenna feed point at 31' and my angle is about a 100* included angle. I am getting an SWR of 1.3 to 1.5 across the band with an element length of just under 100". It's working great, getting good tx and rx and my fs meter shows no radiation from my coax now. Today, the wind is pretty bad, so I guess the mounting and the elements are going to be put to the test.
super simple.
234 divided by frequency in MEGS x VF for length of wire in feet.
example: 234/27.2 = 8.6' x 12 = 103.25" x velocity factor of .985 (my 12 gauge wire) = 101.68" per side,
then,
120* angle = 50ohms if the antenna is at least a 1/2 wave above average ground, this should net you real close to a flat 1:1 swr, and you can do that angle vertically,
- or horizontally by pulling the center toward a 3rd tie point so the entire dipole is flat vertically.
234 divided by frequency in MEGS x VF for length of wire in feet.
example: 234/27.2 = 8.6' x 12 = 103.25" x velocity factor of .985 (my 12 gauge wire) = 101.68" per side,
then,
120* angle = 50ohms if the antenna is at least a 1/2 wave above average ground, this should net you real close to a flat 1:1 swr, and you can do that angle vertically,
- or horizontally by pulling the center toward a 3rd tie point so the entire dipole is flat vertically.
It really depends on the ground. I was using my Avalanche probe most of the summer as a mast for a 20 metre dipole. Most of the time with a 1.1:1 to 1.3:1 SWR.
Not really, not much if it's at least a 1/2 wave above ground, even less variance if it's a full wave length above ground.
People worry too much about swr, as long as it's correct length and resonant it should provide fine performance, with maybe a couple percentage points less in power due to an swr of 1.5:1 vs 1:1
My point which you totally missed was that you stated that "50ohms if the antenna is at least a 1/2 wave above average ground, this should net you real close to a flat 1:1 swr,". The dipole I posted a picture of was 9' at the feed point with a swr of around 1.1:1.
Late to the party and a few cents short . I'll leave this here anyway.
I trim, tune, to resonance. At this point I have no idea what the VSWR is . I used to do this with a GDO* and a noise bridge.
With a simple VSWR indicator I can take an educated guess at whether the Impedance is higher or lower than my feedline. With the Rig Expert or MFJ 'lysers I'd know in an instant. I don't know if you would consider swapping 50 for 75 ohms just to see the difference lazy, hack, or effective, but it's what I do most often.
Then there is the OCFD. Whole different animal.
http://www.w8ji.com/windom_off_center_fed.htm
Learn the difference between a VOLTAGE and CURRENT balun.
http://www.kn9b.us/guanella-balun
http://www.w8ji.com/windom_off_center_fed.htm
Then there are various wire antennas that can exhibit 3,000 ohms or more that need to be stub matched at the feed point to get them close to any kind of feed line.
In any case the idea is not to fool the radio but to keep the VSWR off the feed line.
Now look at that from the radio. Today's radios absolutely need to see as close to a flat match as possible. Older tube outputs would match to at least 3:1 . The radio absolutely needs to see as close to a 1:1 as possible and doesn't care in the least what the feedpoint impedance is. The antenna doesn't care what the feedpoint impedance is as long as it is resonant.
Trim to resonance , keep VSWR off the feedline, and show 50 ohms (or 1:1 VSWR) to the radio.
*grid dip oscillator (for those born after 2k)
Addendum:
I suppose I owe this much after all those words. Never once did I answer or approach an answer to "what is the feed point impedance of the inverted "Vee" for different angles and AGL." It just doesn't matter. YMMV
I trim, tune, to resonance. At this point I have no idea what the VSWR is . I used to do this with a GDO* and a noise bridge.
With a simple VSWR indicator I can take an educated guess at whether the Impedance is higher or lower than my feedline. With the Rig Expert or MFJ 'lysers I'd know in an instant. I don't know if you would consider swapping 50 for 75 ohms just to see the difference lazy, hack, or effective, but it's what I do most often.
Then there is the OCFD. Whole different animal.
http://www.w8ji.com/windom_off_center_fed.htm
Learn the difference between a VOLTAGE and CURRENT balun.
http://www.kn9b.us/guanella-balun
http://www.w8ji.com/windom_off_center_fed.htm
Then there are various wire antennas that can exhibit 3,000 ohms or more that need to be stub matched at the feed point to get them close to any kind of feed line.
In any case the idea is not to fool the radio but to keep the VSWR off the feed line.
Now look at that from the radio. Today's radios absolutely need to see as close to a flat match as possible. Older tube outputs would match to at least 3:1 . The radio absolutely needs to see as close to a 1:1 as possible and doesn't care in the least what the feedpoint impedance is. The antenna doesn't care what the feedpoint impedance is as long as it is resonant.
Trim to resonance , keep VSWR off the feedline, and show 50 ohms (or 1:1 VSWR) to the radio.
*grid dip oscillator (for those born after 2k)
Addendum:
I suppose I owe this much after all those words. Never once did I answer or approach an answer to "what is the feed point impedance of the inverted "Vee" for different angles and AGL." It just doesn't matter. YMMV