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Mono Band Vertical Antennas Using Bamboo Poles

Created by Greg Danes, KJ4DGE on 2020-12-14
Mono Band Vertical Antennas Using Bamboo Poles
By KJ4DGE



I live in a house with a very small yard. Even though it has two large trees in the backyard, putting up a dipole is very hard as they are very close together and we are surrounded by commercial property. The last thing I need is a business owner wondering what crashed through their window in my attempt to throw a weighted object into the trees.

My nearby neighbor has a stand of bamboo running in front of his sidewalk that is at its height some 30 to 35 feet in length. He knows it is something he wishes he could get rid of and culls it often. I make use of this with his permission and take the hardiest and longest cuts for various projects.

Using this bamboo, I have erected multiple receiving and transmitting antennas in an area that is extremely small. Due to the trees they are barely noticeable.

My latest project has been to erect a multiband vertical for 20/40 meters which works superbly. Looking at the higher bands I decided to go the same route but with mono antennas for 10 and later 17 and 15.

This is about the 10-meter model I created in under 2 hours. I already had bamboo mast in place in the backyard at 27 feet. Using the 468/MHz equation I cut two lengths of 16.5-ft house wiring. This is the common type used for 110-volt AC connections. Laying out the bamboo pole I taped the first 16.5 length to it leaving 4 feet from the end for a 4:1 balun box from a previous project that already had a SO-239 connector, screws for GND and was lighter than some other baluns I have.

Using 75 feet of RG58 cable I connected this to the balun and ran the other 16.5 feet from the ground screw to slope off to a stake in the backyard.

I then proceeded to fire up the Ft-990 and check the SWR at 28.300, 28.4 and 28.5. with readings of 1.2.1 and at 28.5 of 1.4.1. Acceptable and the power output across this portion of 10 meters is a full 100 watts.

Contact wise I have not had good conditions to try any 10-meter QSOs. Here are the pics of the finished setup.



 


 

Current balun

 


Feed point. Behind the bushy leaves is a guy wire going around the trunk of a tree. With bricks at the bottom to keep it from moving in the breeze.

 


16.5 foot counterpoise

 



Another view of the counterpoise.

 



Yes, the tree will affect the signal but the end point at the top is in the clear!



To get an idea of how easy this is to make. Short of having a 30 ft. non-conductive mast, all you need is the wire cut to the length you want for the band you want to work some electrical tape, a matching section at the feed point and some coax.

Here are the measurements for mono-band verticals centered (more or less at the center of the band.


10 meters (2) 16.5 lengths of wire
15 meters (2) 22.4 lengths of wire
17 meters (2) 25.7 lengths of wire
20 meters (2) 32.9 lengths of wire


I may try to make this a multiband vertical down the road by adding the 16- and 17-meter radials to another 2 sections of bamboo off the same base. Anyway if you hurting for space, consider going vertical!


KJ4DGE

K0UA2020-12-25
Re: Mono Band Vertical Antennas Using Bamboo Poles
Ummm.............what? The dimensions you have published are for a full wave antenna...which changes the impedance dramatically. If you cut the wires you are using now in half I think it will work much better...with a lot less of a mismatch to the 50 ohm coax you're using. Alternatively you could use open wire line...or window line....to a balanced output tuner. So...for example...on 20 meters the antenna should be about 33 feet TOTAL LENGTH....or about 16.5 ft. on each side.


yeah, tried to tell him that, but he isn't having any. Also he stuck what he says is a 4 to 1 matching transformer in there just for some reason. I don't know why. Then someone encouraged him to "just use what works for you" problem is when you publish erroneous information you hurt others.
Reply to a comment by : K1LNC on 2020-12-25

Ummm.............what? The dimensions you have published are for a full wave antenna...which changes the impedance dramatically. If you cut the wires you are using now in half I think it will work much better...with a lot less of a mismatch to the 50 ohm coax you're using. Alternatively you could use open wire line...or window line....to a balanced output tuner. So...for example...on 20 meters the antenna should be about 33 feet TOTAL LENGTH....or about 16.5 ft. on each side.
K1LNC2020-12-25
Mono Band Vertical Antennas Using Bamboo Poles
Ummm.............what? The dimensions you have published are for a full wave antenna...which changes the impedance dramatically. If you cut the wires you are using now in half I think it will work much better...with a lot less of a mismatch to the 50 ohm coax you're using. Alternatively you could use open wire line...or window line....to a balanced output tuner. So...for example...on 20 meters the antenna should be about 33 feet TOTAL LENGTH....or about 16.5 ft. on each side.
KJ4DGE2020-12-17
Re: Mono Band Vertical Antennas Using Bamboo Poles
Yes to my neighbor's stash of verticals. They do a good job of culling them during the spring and summer, however the damn Larks love the stuff for nests high up and the concrete pathway directly in front of their house is covered in Lark poop sometimes. I gave them a plastic owl to put nearby and someone stole the damn thing. They bought another one and it seems to work.

GSD
Reply to a comment by : KT4EP on 2020-12-16

Put it up and let it work for you. No matter the comments, if it's working as you like it, then go for it. I feel for your neighbor. NEVER plant bamboo. But it's useful for ham radio! I've seen diagrams and instructions for quads made with bamboo arms.
KT4EP2020-12-16
Mono Band Vertical Antennas Using Bamboo Poles
Put it up and let it work for you. No matter the comments, if it's working as you like it, then go for it. I feel for your neighbor. NEVER plant bamboo. But it's useful for ham radio! I've seen diagrams and instructions for quads made with bamboo arms.
KJ4DGE2020-12-16
Re: Mono Band Vertical Antennas Using Bamboo Poles
Thanks to all for the read. I may invest down the road in a NANO VNA to start really looking at these things and see what can be improved upon. The fun is in the building and testing with what limited tools I have.

KJ4DGE
Reply to a comment by : K4PIH on 2020-12-15

Greg, thanks for the article using bamboo for a mast. As a young ham/SWL in Florida, I used bamboo exclusively as it was the only thing I could afford (free from my backyard) and readily available. I once built a quad using bamboo and copper wire salvaged from a transformer. Worked like champ! Keep up the great articles. 73, Jack
Reply to a comment by : K0UA on 2020-12-14

Uh, I hate to tell you this, but you don't use the 468/F formula. you use the 234/F in Mhz formula for a vertical 1/4 wave with a 1/4 wave radial for counterpoise. A couple or more elevated radials would be good, or you can lay them on the ground and they do not need to be so precise, but the vertical radiator needs to be 1/4 wavelength long NOT 1/2 wavelength. 1/2 wave will give a high impedance feed point. You would use a 1:1 choke balun at the feed point also. So a 20 meter vertical would be about your 16.5 feet tall. You can feed multiple wires from one feed point also. In effect a fan vertical. Good luck.
K4PIH2020-12-15
Re: Mono Band Vertical Antennas Using Bamboo Poles
Greg, thanks for the article using bamboo for a mast. As a young ham/SWL in Florida, I used bamboo exclusively as it was the only thing I could afford (free from my backyard) and readily available. I once built a quad using bamboo and copper wire salvaged from a transformer. Worked like champ! Keep up the great articles.

73, Jack
Reply to a comment by : K0UA on 2020-12-14

Uh, I hate to tell you this, but you don't use the 468/F formula. you use the 234/F in Mhz formula for a vertical 1/4 wave with a 1/4 wave radial for counterpoise. A couple or more elevated radials would be good, or you can lay them on the ground and they do not need to be so precise, but the vertical radiator needs to be 1/4 wavelength long NOT 1/2 wavelength. 1/2 wave will give a high impedance feed point. You would use a 1:1 choke balun at the feed point also. So a 20 meter vertical would be about your 16.5 feet tall. You can feed multiple wires from one feed point also. In effect a fan vertical. Good luck.
KJ4DGE2020-12-15
Re: Mono Band Vertical Antennas Using Bamboo Poles
OK James, and no, I do not own an antenna analyzer. But you are right about not let other follow erroneous information.

"A dipole is usually a 1/2 wave antenna, not a full wave. Last measurement is divide the full wave length by 4. In general terms, a dipole for 6m is about 9.25 feet from end to end, a 10m dipole is around 16.75 feet overall, and a 20m dipole is about 33.5 feet total length".

I went with the above information and from what I found on the QRZ forum here:

https://forums.qrz.com/index.php?threads/loft-fan-dipole-for-6-10-20.366170/#:~:text=A%20dipole%20is%20usually%20a%201%2F2%20wave%20antenna%2C,feet%20total%20length.%20Last%20edited%3A%20Oct%2031%2C%202012

So if I am to believe what I read but other more knowledgeable than myself and cut the radiating element for a full wavelength, and using a ground couterpoise of the same length, matched the balun I had to this using what I had 4:1 or 49:1, I then took measurements based on the meter in the FT-990 and made sure I had a choke of 1:1 on a 75 foot coax run for keeping RF current coming back down the line into the shack, and am able to load this up with low SWR, then it may work?

I am sure all you have said is correct and yes, you cannot change the laws of Physics. I have been experimenting with antennas for 16 years based upon the doings of others more knowledgeable than myself and through trial and error.

Long before we had modern instruments that is what Amateur radio experimenters did. Many times failing to get to what worked. The point of the article is not to lead anymore down the wrong path but to spark experimentation in a off the shelf world. I am sorry if I offended anyone's scientific norms.

Greg, KJ4DGE
Reply to a comment by : K0UA on 2020-12-15

Sorry, but you cannot end feed a 16.5 foot piece of wire on 28 Mhz and expect anything but about 2500 ohms as a feed point impedance. That piece of wire is twice as long as it should be for 10 meters. so is the radial. 234/28=8.35 foot. As chief engineer Montgomery Scott used to say "Captain, you can't change the laws of Physics". :) And you don't need a 4 to 1 balun to feed a 1/4 wave vertical. It feed point impedance is around 36 ohms, give or take, and makes a pretty fair match to 50 ohm coax without any impedance transforming device. It is a very good thing that you took the time to publish an Article, and take pictures to go with it. But you wouldn't feed an end fed 1/2 wave antenna with a 4 to 1 balun very successfully. I cannot let erroneous information be put out there for others to follow, down the rabbit hole as I know it. If others would like to either back me up or back me down, than that would be appreciated too. I sincerely hope this does not discourage you in any way. Again I applaud you for your efforts and nice write up. 73 James K0UA
K0UA2020-12-15
Mono Band Vertical Antennas Using Bamboo Poles
So lets take a look at the transformation ratio of that "black box" since we disagree on what it is. Do you have an antenna analyzer? If so, and you believe it to be a 4:1 than place two NON inductive resisters of 100 ohm value in series across the output of the device. This will make the load on the DUT (device under test) 200 ohms. If it is a 4:1 then when you scan across the HF spectrum with your analyzer you should read a near 1:1 SWR across HF at least until you get to the top end. I am suggesting you probably have a 49:1 transformer and if you place a 2500 non inductive load across the DUT then you should have a near 1:1 SWR across the bands. This will let you know what that Device is actually doing. You need to prove this to your self.
K0UA2020-12-15
Mono Band Vertical Antennas Using Bamboo Poles
Sorry, but you cannot end feed a 16.5 foot piece of wire on 28 Mhz and expect anything but about 2500 ohms as a feed point impedance. That piece of wire is twice as long as it should be for 10 meters. so is the radial. 234/28=8.35 foot. As chief engineer Montgomery Scott used to say "Captain, you can't change the laws of Physics". :) And you don't need a 4 to 1 balun to feed a 1/4 wave vertical. It feed point impedance is around 36 ohms, give or take, and makes a pretty fair match to 50 ohm coax without any impedance transforming device. It is a very good thing that you took the time to publish an Article, and take pictures to go with it. But you wouldn't feed an end fed 1/2 wave antenna with a 4 to 1 balun very successfully. I cannot let erroneous information be put out there for others to follow, down the rabbit hole as I know it. If others would like to either back me up or back me down, than that would be appreciated too. I sincerely hope this does not discourage you in any way. Again I applaud you for your efforts and nice write up. 73 James K0UA
KJ4DGE2020-12-14
Re: Mono Band Vertical Antennas Using Bamboo Poles
The balun box is a 4:1 and if you look before that you have a hand wound 1:1 choke. This works well for loading the 10 meter. On my 40/20 vertical using (without a balun) but a home-brew loading coil about 1 1/2 feet below the vertical element and it still has 2 16.5 radials at about a 40 degree angle and one 26 foot radial for the 40 meter side. Yes to the 234/MHz misquote, thanks for the correction.
Reply to a comment by : K0UA on 2020-12-14

Uh, I hate to tell you this, but you don't use the 468/F formula. you use the 234/F in Mhz formula for a vertical 1/4 wave with a 1/4 wave radial for counterpoise. A couple or more elevated radials would be good, or you can lay them on the ground and they do not need to be so precise, but the vertical radiator needs to be 1/4 wavelength long NOT 1/2 wavelength. 1/2 wave will give a high impedance feed point. You would use a 1:1 choke balun at the feed point also. So a 20 meter vertical would be about your 16.5 feet tall. You can feed multiple wires from one feed point also. In effect a fan vertical. Good luck.
K0UA2020-12-14
Mono Band Vertical Antennas Using Bamboo Poles
Yes, the DX commander is just a fan vertical. He uses on ground radials and they are not 1/4 wave in length either on most bands, ON ground radials do not need to be 1/4 wave long to have an effect. Elevated radials are tuned 1/4 wave radials. And you don't need so many of them. On his 40 meter element his folds a bit of it back down. Mainly because the pole is not 33 feet high (at least on some models), but it also give a bit better 15 meter response as a 3/4 wave vertical.
KD1JT2020-12-14
Re: Mono Band Vertical Antennas Using Bamboo Poles
Isn’t that the way the DXCommander works?
Reply to a comment by : K0UA on 2020-12-14

Uh, I hate to tell you this, but you don't use the 468/F formula. you use the 234/F in Mhz formula for a vertical 1/4 wave with a 1/4 wave radial for counterpoise. A couple or more elevated radials would be good, or you can lay them on the ground and they do not need to be so precise, but the vertical radiator needs to be 1/4 wavelength long NOT 1/2 wavelength. 1/2 wave will give a high impedance feed point. You would use a 1:1 choke balun at the feed point also. So a 20 meter vertical would be about your 16.5 feet tall. You can feed multiple wires from one feed point also. In effect a fan vertical. Good luck.
K0UA2020-12-14
Mono Band Vertical Antennas Using Bamboo Poles
Are you sure that "balun box" is not a 49:1 transformer? because that would be about right for en end fed 1/2 wave which is what you have there. The impedance of an end fed 1/2 wave is about 2500 ohms or so.
K0UA2020-12-14
Mono Band Vertical Antennas Using Bamboo Poles
Uh, I hate to tell you this, but you don't use the 468/F formula. you use the 234/F in Mhz formula for a vertical 1/4 wave with a 1/4 wave radial for counterpoise. A couple or more elevated radials would be good, or you can lay them on the ground and they do not need to be so precise, but the vertical radiator needs to be 1/4 wavelength long NOT 1/2 wavelength. 1/2 wave will give a high impedance feed point. You would use a 1:1 choke balun at the feed point also. So a 20 meter vertical would be about your 16.5 feet tall. You can feed multiple wires from one feed point also. In effect a fan vertical. Good luck.