Why does my homemade Yagi wifi antenna perform so poorly?
Can somebody tell me why my home made 20 element Yagi directional antenna does not seem to have much ?gain?? It does not seem to increase the range of the wifi extender (Amped Wireless High Power Wireless-N 600mW Smart Repeater and Range Extender (SR10000), see this Amazon link ) that I want to attach the home made antenna to. In fact I think it picks up fewer wifi networks, with less strength, than a simple (detachable) 5dBi omni-directional antenna(s) that came with the extender.
I made the home made antenna in accordance with the instructions at this link,
https://www.ab9il.net/wlan-projects/wifi6.html ; the driven element is a folded dipole antenna.
I have attached a screenshot from that website showing the antenna element lengths and spacing and also pictures of the actual antenna I constructed. These pictures show the antenna (elements made of 14 AWG copper wire with green insulation) attached with scotch tape to a plastic white ?foam board? I bought at the dollar store. (The glass has water in it). Other pictures show the cable I am using to connect the folded dipole element to the extender and the soldering of the cable to the folded dipole element. But as I said, when I connected completed antenna to the wifi extender described above it did not perform well.
I have two possible explanations for the poor performance, the first, that it needs a balun is the explanation I am most inclined to think is the correct one. The second, less likely (I think), explanation is that I should have stripped the insulation off the 14 AWG copper wire that I used to make the elements of the antenna.
The wireless extender has a female RP- SMA input (wikipedia link) for each detachable antenna, and I am using a coaxial cable that has a compatible RJ-SMA connector. The coaxial cable is about 0.109 inches in outside diameter. It might be RG-174/U. I scavanged the cable from an Intel device (G577005-002) that looks like one at this Amazon link for an Intel Dual Band Wireless-AC 7260 plus Bluetooth Adapter . I am unsure the exact type of coaxial cable. It is probably 50 ohms impedance, but I do not know for sure.
If it needs a balun, I?d be willing to make one if it?s not too difficult or buy a balun if its not too expensive.
QUESTION(S): Does anybody have any suggestions? Should I make (or buy) a balun? Should I take the insulation off of the elements that are made with wire?
Thank you,
Amateur
Where is the folded dipole?
The ends of the feeder cable need tidying up (they are part of the dipole) but they should go to the ends of the folded loop.
Folding the dipole reduces its impedance to match the cable better, without it there will be very significant signal loss.
The insulation on the wires is irrelevant, a balun might make a tiny difference but folding the dipole is the real issue.
It looks nothing like the one in the web page, have you taken into account the effects of whatever it is built on, the original uses a boom and the elements are in free space.
Brian.
As shown in the picture, it's a straight 60 to 75 ohm half wave dipole, not a folded dipole. This makes sense because it's roughly matched to the 50 ohm cable, however it misses at least a ferrite core over the coax cable end or a dedicated 1:1 balun.
For such an antenna, you need to be much more precise with dimensions. I don't think you have a chance to realize it with your low mechanical precision.
Brian,
Thanks for your reply. The pictures are somewhat misleading, because the white foam board is opaque. Element #2 actually goes through two holes in the foam board and "folds" around the foam board to form a folded dipole. In other words, you cannot see that element # 2 (the driven element) in the "top view" (that shows all 20 elements) is actually essentially a loop: the "ends" of element # 2 wires go through holes in the foam board. The two pictures showing the soldering to the cable shows the underside of the loop. In other words, those two pictures show the continuation of the wire from the top view. (By the way, element #1 is a reflector.)
My design is a" poor man's design" that does not require a drill. The boom in the online design at the link I gave is wooden and requires a drill to make holes to mount the elements in the boom. But I tried to reproduce the online design at the link as best I could. The online design at the link shows the top of the folded dipole in the same plane as the other non-driven elements. And that is what I tried to do by affixing the top of my driven element and all the non driven elements to the same surface of the foam board. There is essentially nothing directly between the elements, except for the green wire insulation (and some clear scotch tape used to affix the elements to the foam board). On the other hand, perhaps the foam board distorts the field around the elements in some way? I am not sure.
When I tested my design, I tried pointing it in several directions and in different orientations. And it does work better than no antenna at all connected to the extender. But it is no better and probably worse in performance than one or two of the simple omni-directional antennas that came with the extender.
Any comments your or others have will be greatly appreciated.
Thanks again,
Amateur
Thanks for your reply FvM, The pictures are somewhat misleading, because the white foam board is opaque. Element #2 actually goes through two holes in the foam board and "folds" around the foam board to form a folded dipole. In other words, you cannot see that element # 2 (the driven element) in the "top view" (that shows all 20 elements) is actually essentially a loop: the "ends" of element # 2 wires go through holes in the foam board. The two pictures showing the soldering to the cable shows the underside of the loop. In other words, those two pictures show the continuation of the wire from the top view. (By the way, element #1 is a reflector.)
My design is a" poor man's design" that does not require a drill. The boom in the online design at the link I gave is wooden and requires a drill to make holes to mount the elements in the boom. But I tried to reproduce the online design at the link as best I could. The online design at the link shows the top of the folded dipole in the same plane as the other non-driven elements. And that is what I tried to do by affixing the top of my driven element and all the non driven elements to the same surface of the foam board. There is essentially nothing directly between the elements, except for the green wire insulation (and some clear scotch tape used to affix the elements to the foam board). On the other hand, perhaps the foam board distorts the field around the elements in some way? I am not sure.
See my reply to Brian's post for a little more detail.
Thanks,
Amateur
Volker,
Thanks for your reply. How precise do you think one has to be? In the online design at the link I gave, the designer said to within 0.5 mm was sufficient. I tried to do that as much as I could. Do you have any more specific suggestions as to how to achieve more precision?
My design is a" poor man's design" that does not require a drill. (I made two holes in the foam board with a simple awl.) The boom in the online design at the link I gave is wooden and requires a drill to make holes to mount the elements in the boom. But I tried to reproduce the online design at the link as best I could. The online design at the link shows the top of the folded dipole in the same plane as the other non-driven elements. And that is what I tried to do by affixing the top of my driven element and all the non driven elements to the same surface of the foam board.
See some more information in my other recent posts for today.
Any comments from you or others will be much appreciated.
Thanks,
Amateur
Thanks FvM,
Do you have any suggestions for how to improve my situation? Can I make a balun or buy a balun? Can I improve the coax connection in some way?
The present coax connection is a solder joints of the coax central conductor to one end of the folded dipole and a solder joint of the coax sheath (that has been twirled into a kind of braid) and the other end of the folded dipole.
Do you think I can amend my current "poor man's design?"
Thanks,
Amateur
Thanks for mentioning the foam board. So it's actuality a folded dipole. Unfortunately it's seriously mismatched in this case, having typically 290 ohm impedance. In addition you have the problem of asymmetrical coax connection, making the cable become part of the radiating element.
I see that the website also uses a folded dipole without an impedance matching balun. Bad idea.
A simple solution, keeping the already designed folded dipole, would be a lambda/2 coaxial balun.Many previous threads at Edaboard discussing it. E.g. https://www.edaboard.com/showthread....-Folded-Dipole
Thank you FvM,
What kind of cable should I use to make the balun at the link you gave? The same coax cable I am already using? Do you think it will make a major difference in performance?
Regarding the asymmetry of the coax connection, how do I cure the asymmetry? Should the cable be more midline to make it more symmetric or something? I have attached a picture of one of the soldered connections from the online website. Is that online example of a soldered connection better or more symmetric?
Thanks,
Amateur
The page at this link http://vk5ajl.com/projects/baluns.php#voltage seems to say that you can use a different cable to make a balun than the cable used to connect to the driven element: "It is important use the best coax you can for the balun even if you use lousy coax for the feedline. Using heliax is a little impractical because it doesn't bend so easily but something like Benelec LMR400 is ideal."
What about RG6 or RG59 cable for making this kind of balun, would either of those cables be OK for making a balun for this situation?
Thank you,
Amateur
I agree that usually the folded dipole has some 4:1 balun, but it's not always true. The dipole inside a yagi isn't the same as that dipole stand-alone. The impedance is influenced by the reflectors & directors which are close to the dipole. For example, I recently simulated this special design (dipole with two directors for dual beam) and it has perfect 50 Ohm match without 4:1 balun:
It think 1% tolerance on the length is acceptable. Some yagi designs are more critical than others. In general, I expect many elements to be more critical. The special bi-directional 3e-element that I linked above is extremely narrowband, but a normal 3-element would be much less sensitive to tolerances.
Sounds ok. But your feed with the coax is rather large compared to the element lengt, so that fore sure will create a lot of parasitic inductance. I think you would need to go from coax to dipole feed with much less undefined extra length.
Also, your wires for the elements are rather thick compared to the length. That is possible, but wire radius will change the element length. Are the length calculated for this wire diameter?
And wire insulation (=dielectric in the area of high electric field) should be removed.
Wood for the boom or foam, all that has an effect on tuning of the elements. I don't think your design with many elements will perform as expected. Go for less elements, which hopefully is more robust to tolerances.
You are right, driving element impedance depends on the reflector and director spacing. I found this table in Balanis Antenna Theory. Numbers are for regular half-wave dipole, folded dipole has 4x this impedance.
A full featured yagi design tool should be able to calculate the impedance, I didn't find respective comments in the linked antenna design.
Thanks Volker, It may be that the need for a balun depends on the design given that I was following.
OK thanks Volker, I will take that into account.
Ok I will think about this. I looked at my connection and the connection of the online design (that I used as a guide) and I do not see a big difference in terms of lengths, so I am not sure exactly what you mean. Can you please be more specific and elaborate on this?
I think the solder connections used online are "cleaner", but I think mine are structurally/mechanically stronger, due to the larger size/more solder. Frankly the solder connections of the online design looked weak. Also I just want to be sure you realize that the picture in your post that you circled in red is NOT my design, but is from the design that is online that I was using as a guide.
Volker, the actual wire conductor is 14AWG copper, which is the same size wire (& metal) in the online design I used. I tried to read up on this and concluded, as you say, that dielectric properties will affect performance. I figured that wood and plastic foam, being a lot of air, would have the same dielectric properties as air & vacuum. I can remove the insulation, that is not a big deal.
Like I said above, I figured that wood and plastic foam, being a lot of air, would have the same dielectric properties as air & vacuum.I do not have a drill to use to make holes in wood, I just used an awl to make the two holes in the foam board for the folded dipole.
I tried to access the calculator used for the online design I used as my guide, but I could not access it, the links were confusing and seemed to be nonfunctional. From what you are saying, it sounds like you think I should start over with a new design. For that I will need a design tool that I can get online.
Can you or anybody else answer my question in my previous post about the type of cable that can be used to make a balun?
Thank you,
Amateur
As I said in my previous post, I tried to access the calculator used for the online design I used as my guide, but I could not access it, the links were confusing and seemed to be nonfunctional. Perhaps the presence or absence of a balun depends on the particular design.
From what you are saying, it kind of sounds like you think I should start over with a new design. For that I will need a design tool that I can get online. can you suggest an online design tool? Can I still use 14 AWG copper wire in another design tool?
Having said that I am not yet completely convinced I have to throw away all the work I have already done.
Can you or anybody else answer my question in my previous post about the type of cable that can be used to make a balun?
Thank you,
Amateur
By the way, I emailed the website of the online design that I used as a guide for the antenna that I made and asked if a balun was needed. So far there has been no reply to my question.
Thanks,
Amateur
As I said in my original post, the online design I used as a guide is at this link https://www.ab9il.net/wlan-projects/wifi6.html which says " "Yagi wi-fi antennas can be rather difficult to build, but it can be done if you measure precisely and cut precisely. The hard mathematical design work for the wi-fi antennas shown here was accomplished elegantly using a yagi antenna modeler, created by Kevin Schmidt (W9CF) and Michael Lee." That modeler is at this link: http://fermi.la.asu.edu/ccli/applets/yagi/yagi.html , but I could not access the modeler or get it to work. If anybody else can access it or get it to work, please post how you were able to do it.
Thanks,
Amateur
Yes, I understand this isn't your design, but both have "uncontrolled" wire length of several mm length between coax and dipole , which means several nH series L, which menas some dozen Ohm of series reactance. And that detunes your dipole. You would want to measure the actual input impedance (or VSWR).
I recommend to use a short length of really thin coax, so that all that wiring can be smaller. Teflon cable is nice from a practical viewpoint (tolerates heat when soldering) and low loss.
For using coax feed with a dipole, you always need some balun for doing the balaned to unbalanced conversion, even if there is no need for additional impedance transformation. A replacement might be some turns of coax cable, or other tricks as discussed here: http://dg7ybn.de/Symmetrising/Symmetrising.htm
volker,
I appreciate the replies you and others have made. I actually have a degree in physics and EE, but I never studied antenna theory and it has been years since I have thought about impedances, reactance, inductance, etc. I still understand a lot though. I know that at these high frequencies and short wave lengths, all kinds of strange things can happen with effective capacitance, inductance, etc occurring and that dimensions & lengths are critical. Regarding measuring VSWR & SWR, I just read about it and have a rudimentary understanding. I would need a meter to measure VSWR however.
Someday I may invest the time to get a deeper understanding of this subject, because it is fascinating that human beings can communicate through thin air, isn't it? I have felt that way since I was a kid. But in the mean time, I am (more or less) just looking for a simple cook book type design that I can follow. So I am interested in people giving me some hints based on educated guesses, as you have already done thanks! There is another link to a "popsicle stick" design (that is based on the AB9IL website that I used) at this link https://www.instructables.com/id/Eas...-Yagi-Antenna/ .
The comments section at this link are very helpful under the 3 individual commenters Saarducci, zwzserver and myjunkmailbox2013. These 3 commenters address the (unaddressed) impedance matching issue, and the connection of the coax to driven element. At least two of the three recommend a simple dipole as opposed to a folded dipole. I think I may use the simple dipole and try to follow myjunkmailbox's suggestions for making the connection between the driven element and the coax. He (she?) says to get the two inner parts of the simple dipole very close together, about 1mm apart and to use the same length of wire to attach each to the coax. I think I will also strip off the insulation for the 14 AWG copper wire that I am using to make my elements. I am already using very thin coaxial cable as it is, about 0.109 inches in outside diameter. (It might be RG-174/U.)
Any more hints and educated guesses you or others an give me, especially if based on reading the three commenters, Saarducci, zwzserver and myjunkmailbox2013, will be much appreciated.
I think I am still going to try to use my foam board, you can write on it, it's pretty sturdy and it is very low in density, so I think it's dielectric coefficient is closer to 1 than most of the stuff I can use for support, including wood. I may, however, just use a thin strip of the foam board as a boom, so that the elements generally stick out into air (as is common for all the online designs I have seen). I may, however, reinforce the thin strip so it does not sag and all the elements are in the same plane.
In addition, I do not want to do anything that will burn out my wifi extender (by somehow drawing too much power out of the transmitter into the antenna). So any hints there will be appreciated too.
Thanks,
Amateur
Just in the way of a little more explanation about educated guesses with respect to the 3 commenters, I have attached pictures from the posts of commenters myjunkmailbox2013 and zwzserver at
https://www.instructables.com/id/Eas...-Yagi-Antenna/ . These pictures illustrate their suggestions for attaching the driven element to the coax and for impedance matching or balun construction. See below. More info is available in their respective comments at the above link, as well as the comments of Saarducci.
Thanks,
Amateur
You'd better to put a simple PCB just underneath the Dipole and assembly it with proper PCB type SMA Connector otherwise you cannot be sure about antenna performance..
Thanks Big Boss, I will consider that type of connection.
I have concluded that I am going to reconsider my situation at this point. And I am going to slow down & try completing this Yagi later. But, I have a couple of quick questions if anybody cares to answer.
1) A lot of people on this forum use the Yagi calculator here http://www.vk5dj.com/yagi.html, are there any other Yagi calculators (especially for a 2.4 GHz) that people can recommend?
2) Some people recommend using a simple dipole antenna as the driven element for a Yagi (2.4 GHz) instead of the folded dipole. Does anybody have any comments about the relative advantages/disadvantages of either strategy?
3) Does anybody have any more comments about the connection (I think this is called the antenna feed) between the driven element and the cable (for a 2. GHz Yagi) that goes to the device (in my case a wifi extender)?
I thought a 2.4 GHz Yagi antenna would work for several different situations & needs and be easier to make and need lower tolerances than has turned out to be the case. As I said previously though, I think the foam board has lots of promise as a boom material. It can be glued together and laminated (and used/glued on edge) to make it sturdy so that it does not droop as boom length increases. It also is very low density, so I think its dielectric properties are close to air.
The online calculator at design page I originally used https://www.ab9il.net/wlan-projects/wifi6.html does not work. The Yagi calculator here http://www.vk5dj.com/yagi.html that a lot of people on this forum use gives useful information, including how to construct a balun. Any other comments on this calculator would be welcomed.
Thanks,
Amateur
Hello,
Can anybody tell me the advantages and disadvantages of using a simple dipole compared to a folded dipole as the driven element in a 2.4 GHz (wifi) Yagi antenna?
Is there, for example, a difference in gain?
I am presently constructing such an antenna from 12 gauge copper wire (using an antenna calculator). The simple dipole is easier to construct in terms of getting dimensions to be correct. And the 4:1 Balun that has a 41mm loop for a folded dipole is not that easy to construct either.
It seems to me that a simple dipole may have some advantages, for example, this thread on this forum has a post by vfone that recommends a simple dipole instead of a folded dipole: "At 2.4 GHz I would recommend do not use a folded dipole for the driven element, because anyway the bandwidth of a standard 1/2 lambda dipole (~73 ohms) at that frequency usually covers the desire bandwidth. The balun would be simpler as a: sleeve, or gamma, or resonant stub, etc. Check the net for various examples."
vfone's post gives this link as an example of a balun for a simple dipole
Also are the baluns for a simple dipole easy to construct when the simple dipole is used in a 2.4 GHz Yagi antenna?
Thank you,
A.