A Folded Dipole for 2-meters (70-cm?) (048)
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- เผยแพร่เมื่อ 9 ม.ค. 2023
- I created a video a few weeks ago showing how to create a 4:1 BALUN using coax. In this video I created a 4:1 BALUN for the Amateur Radio 2-meter band, centered on 146 MHz.
Someone asked the question,"Why would you ever need a 4:1 BALUN for the 2-meter band?"
GOOD QUESTION!
In answer to this, I am going to show you how to create a folded dipole antenna for the 2-meter band using the 4:1 BALUN previously created as the impedance matching device.
I will create two distinct version of this antenna:
1. The Solid Wire Version using #4AWG solid copper wire
2. The Copper Tubing Version using 1/4-in OD copper tubing.
I will test this antenna on both the 2-meter and 70-cm bands. The results may surprise you.
Here are the promised links for you:
===============================================
4NEC2 Modelling Program Download
www.qsl.net/4nec2/
4NEC2 Model for the Folded Dipole
drive.google.com/file/d/1fWF0...
Time Markers for Your Convenience
----------------------------
00:05 Introductory Comments
01:40 The Plan: 4NEC2 Modeling
07:34 The Bending Jig
08:26 How long do we cut our wire?
11:28 Cutting the wire
12:06 Creating the Antenna using the bending jig
13:20 Preparing for Test
13:23 Tinning the Feedpoint
13:40 Create a Mounting Point
14:41 Connecting the BALUN/Feedline
14:47 Testing Begins
14:59 Call to reality on results ...
15:40 Test Results
15:55 Test Result Debriefing
16:51 The Tubing Version
17:29 How long do we cut the tubing?
18:33 The Assembly Procedure...
19:41 The Actual Build-bending the tubing
20:08 Trimming the excess
20:31 Preparation for testing
20:32 Tin the Feedpoint Ends
20:40 Create the Mounting Device
20:54 Connect the BALUN/Feedline
21:02 TESTING
21:05 Test Results on 2-meters
21:17 What about 70-cm?
22:32 Create a more substantial mounting plate
23:59 Testing the Modified Antenna
24:03 Test Results on 2-meters
24:25 Test Results on 70 cm
25:01 How much lighter is the Tubing Version?
25:34 Final Comments and Toodle-oots
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I have not watched the video yet but folded dipole caught my eye.
I used to build 3 or 4 element Yagis for 2, 6, & 10 meters and learned that having a compact or short boom thru a close spacing resulted in a low impedance which could be brought up to 50 or close to 50 ohms by using a folded dipole with the right seperation between wires. I ended up with some very good compact Yagis.
Since I am not a big fan of DXing and use my antennas for other things such as conversations within 500 miles or radio astronomy many of my antennas are NVIS or at the very least have a high take off angle by being low to the ground. Once again I offset the lower impedance by being low to the ground with a folded dipole configuration. I found normal audio speaker wire often does the trick.
After watching your video I see we essentially did the same thing in reverse. You needed the balun to bring SWR down & I needed folded dipole to bring SWR up.
Incidentally, I'd probably not care about fancy looking and used squared off ends using normal 1/2 inch water pipe and right angle fittings or elbows. What you get in return for looks less cool is an even greater spread with good SWR due to the increased skin & likely easier to construct.
Yes, it is amazing how many and varied ways one can find to make functional antennas! 🙂
Well done Sir.
Thank you for your time.
Thanks for being so helpful with viewer's questions.
You're a blessing,
I appreciate John 3:16, AMEN.
73
Thank you and you are very welcome! That's all what this channel is all about. 🙂 Jesus is the reason I am here! 😁
Well done < and having worked for MTS in M.B.you mentioned Moose lake , My father-in-law worked for Mts in The Pas William or Bill Forester You may have known him
Thanks so much!
Small world!! Sorry, I do not remember Bill Forester. We lived in Moose Lake from 1992 to 2000. 🙂
Suggestions for bending:
(less desirable) -- fill tube with water and chill to hard mushiness (not solid ice). Bend around form and let "ice" melt. Then evacuate
(much better, but messier) -- fill tube with white beach sand (dry and clean). Bend around form and evacuate sand from tube ....
I've heard of the sand one. I was *almost* tempted to try it myself. Never heard of the water method. Thanks for the input! 🙂
when you were bending copper wire, I was thinking I hav many size copper tubing in shop, Then you started on tubing,,,,,great video, as always
Thanks, man!
The working out the band radius and your tips brilliant. Nylon cutting board will eventually disintegrate under sunlight, as has happened to mine in the past. Thanks for posting, Barry, vk2fp/ag7vc
Thanks!
Copy on the cutting board. I did an experiment with some. I took one raw piece and another I painted with a black "Krylon Fusion for Plastic" paint. I left them both out in the weather/sun. It was amazing the difference between the two. The second weathered *MUCH* better than the first. 🙂
Very cool. I've been sharing your channel & vids with some of my other club members. I'm learning every time I watch one. K0ATV
I am so glad that I am making a difference. This is my sole purpose here. Thank you for the encouragement! :-)🤓
Hi there. It's G1bki in the UK. Nickname is George. For info I have used many years ago car brake pipe. Low Cost and strong. Also as its hollow I have inserted garden wire at each end as it can slide in and out for tuning swr etc. Also used on a circular aerial. Cheers from old George
Thanks for the idea! 🙂
n up the wire that you are using - fasten one end in a vice and insert the other in a speed controlled drill after a while of spinning the wire will so hard that it will be self supporting I use this method often for varies uses and it works very well
That is an interesting thought. Never heard that before. 🙂
👍
You need a feed point impedance of 200 OHMS for a 4:1 balun called a beta match.
And that is exactly what I applied to this antenna ... a 4:1 BALUN using coax. I have a detailed video on the how and why of such a coax-based 4:1 BALUN here: th-cam.com/video/fG7ZpsjXRW8/w-d-xo.html
🙂
Since this antenna is already 300 Ohm and balanced at the feedpoint, why not use 300 Ohm twinlead as the feedline? The feedline will be far less lossy than any Coax you could buy. Then you could put the balun at the radio end (Indoors and dry) and reap the benefits. Plus, you will have the opportunity to tinker with the balun for even a better match into the antenna.
Your idea does carry some merit for installation situations which would allow it. For those folks who can do this and want to do it, go for it! It is a reasonably decent idea.
It just occurred to me ... with a 4:1 BALUN and an SWR of nearly 1:1, given that this is an inverted vee and not a dipole, the actual impedance of the antenna here is probably closer to 200 Ohms. The impedance is adjusted, in part, by changing the angle between the legs. This I did to bring my SWR down a bit. Thus, twin lead at 300 Ohms ... not necessarily a good match.
Without going into my installation situation, the convenience of coax far outweighs the benefit of twin lead here. 🙂
If you put 4 of these together in a row, how to figure out the spacing?
Great question and no easy answer because it depends on what you are trying to do with them. This involves two aspects: (1) the physical spacing (2) the phasing which is accomplished by the impedance, length and velocity factor of the cable harness that connects them to each other and to the feedline.
You can play with all of this in 4NEC2, antenna modeling program (FREE).
I have played with a phased array (mine was four square as opposed to stacked) inside 4NEC2, but I've never actually built any of this stuff. :-(
Sorry I couldn't be of more help, but thanks for the comment and question! :-)
I make 137 cm. Dipole for 100mhz fm 300 ohm impedance. For convert 75ohm coaxial balun wire lenth = ?cm. Please guide me.
Well...the quickest and most complete way to help you here is to point you to my video on how to make that 4:1 BALUN that you need using just some coax.
You will find that video here:
th-cam.com/video/fG7ZpsjXRW8/w-d-xo.html
This video will walk you through step-by-step how to make one and why they work.
Hope this helps.
I would make a dipole antenna not folded. Dipole is easier to work with and is a 50 ohm antenna. A L C match can be constructed very easy using a table which can be found in a ARRL handbook.
Yup, dipoles are easier. I honestly haven't built one for VHF, so I do not know how well they would cover the whole 2M band. The advantage of the folded dipole is bandwidth. I built an 80M folded inverted vee and it nearly covers the entire band within reach of my antenna tuner. It's plain old inverted vee predecessor didn't even come close. Enjoy! :-)
To get a 1 to 1 standing wave.
Gotcha. 🙂
what improvement in gain do you get with this folded dipole as compared to a regular dipole?
Ya know, I am not sure. I'd have to run the simulations of the two to discover the answer to this question.
@@eie_for_you I have a request for a video. VNA and Smith charts will tell us what we need to do to match an antenna system to a radio, however no one has ever made a video of actually showing that matching and practice. For instance if it says to put a 470 picofarad capacitor and a 50 micro Henry inductor to match the antenna how do you do that how do you add these components to an incentive system what is the proper way to do it what is the best way to do it I am clueless and I have not seen any videos of anyone else ever showing how to do it either
Would really be appreciated if you could show how to add The recommended components to an antenna system so that it will match it according to the VNA or according to the Smith chart
@@PatAutrey Hmmmm, an interesting thought. I will add this thought in my list of potential videos to create. Thank you for the suggestion! 🙂
Here is a quick answer to the question for your benefit. If you used the VNA to measure the impedance at a particular spot and used this impedance to determine the required matching network components, then this matching network would have to be applied at the same spot that you measured the impedance at. Alternatively, you could do the same if you were another 1/2 wavelength (electrically speaking) away from that point along your feedline because the impedance reoccurs at 1/2 wavelength intervals.
I hope this quicky answer helps.
@@eie_for_you thanks for the quick reply I understand the idea of using a half wave coax so that it remains the same but where I'm confused is what do you use if it asks for a capacitance do you just get a capacitor or do you get a coax that acts like a capacitor I've just never added any tuning components to a system before and I'm unfamiliar with the process of how you physically do it
@@PatAutrey Another quick answer would be that doesn't matter if it a piece of coax that looks like a capacitor or a real, physical capacitor component, as long as it "looks like" a capacitor.
Here is an example in creating a stub match to make that folded dipole match to a 50 Ohm coax.
th-cam.com/video/LY4GysxSEa0/w-d-xo.html
For SSB the dipole has to be horizontal and i don't understand the the dimension i just need inches.
I give the dimensions in both english (imperial) and metric. You will find them all there. If you open the antenna modeling file, you will find them all in feet.
I use this antenna for SSB all the time and get way awesome signal reports. Hope this helps. 🙂
the other comment got messed up it was meant to read To stiffen up the wire you are using ..........
Yup...I figured that out. Thanks for the clarification, though. 🙂
thank you for your lectures --very help full --better than ask Dave ha ha zs1bbg
Ok, so..eh, but 70cm band is 430-440 MHz here..swr is no good.
Here in the states our 70cm band is from 420-450 MHz with a whole bunch of repeater frequencies huddled at the top end of the band. It is at the high end of the U.S. 70cm band where the version of the antenna that I built has an adequately low SWR to be useful. Below that, you are right...SWR climbs rather quickly. 🙂
To bend soft copper tubing, get the lenght that you need plus some ( put the end of copper tubing in a vice and squeeze end shut fill the copper tubing with silica sand and do same with other end ) you can now bend it around any diameter do not have to buy different jigs MaverickIA walking north@walkingnorth4474
Yeah, I've heard that (too late before I spent the $$ on the tool). Sounds like a pretty slick way of doing it. Plus it means unlimited angles ... I could make a helix if I wanted to! 🙂
@@eie_for_you Do you help with questions about ham radios
@@walkingnorth4474 I am a ham and, yes, I do answer questions about ham radios ... depending on the question. Try me. 🤓
@@eie_for_you I have a 10 Tech Delta 2 model 536 I replace the coin size battery for the clock Now it seems like that I cannot add frequencies to memory I enter one frequency and save it and then add another I will not keep the first one I do have the manual and schematics Appreciate your help
@@walkingnorth4474 First, I am assuming that the reason why you replaced the coin cell is because you were having issues with the radio remembering things.
A LOT of these radios have solder-in coin cells 😳. This always puzzled me cuz they gotta know that they are going to need to be replaced!
Here would be exactly what I would do:
If this is a solder-in device, I would do 4 things, fixing as I go:
1. I would use a voltmeter to check the voltage on the battery (it could have been damaged / overheated in the process of soldering it in).
2. I would verify that the new battery was soldered in with the right polarity (*easy* to switch this up with some batteries)
3. I would carefully inspect the solder joints. Make sure they have flowed properly and making good connection.
4. I would very, very carefully inspect the traces leading to the battery pads to be sure that they haven't been cracked or broken. This can happen *very* easily especially when wrestling with unsoldering the the old battery. These cracks can be very, very small...use a magnifying glass.
If it is a socketed battery, I'd first make sure the battery is in the holder in the right orientation and protective tapes taken off of it. Then I would do 3 and 4 from above.
Hope this helps. 🙂