cable connection for 2.4ghz yagi antenna construction - Page 1
Forum section: electronics / rf-microwave

author: jack9
author_rank: Newbie
timestamp: November 02, 2020, 01:28:31 am
content: helloi am attempting to make my first yagi antenna and have a few questionsa short pigtail is recommended to avoid signal loss. if i use RG-6 cable with low impedance, can a long run be permitted?if i trim off the di-electric layer of the cable to accomodate a smaller connector, how would this affect the signal?thanks

author: TheSteve
author_rank: Unknown
timestamp: November 02, 2020, 07:45:36 pm
content: I think I can safely assume your antenna and the radio you wish to connect it to will have a 50 ohm impedance. RG6 however is 75 ohm, so it should not be used for this application.It's never ideal to use a connector which doesn't properly fit. And cable loss at 2.4 GHz is terrible, so shorter is much better.

author: geggi1
author_rank: Frequent Contributor
timestamp: November 02, 2020, 08:05:17 pm
content: For 2,4Ghz I recomend to use pre-made cables.The reason for this is because of the cable loss and to ensure that the connectors are properly installed.There are plenty of pre-made pigtails meant to be used for wifi just be aware that they are normally RP type.When working with high frequencies the first thing to do is to determine the required cable length and then go for the datasheets and check the loss. For Ghz and above the connectors are very important SMA and N-type is more or less the standard, but TNC can also be used.

author: Sal Ammoniac
author_rank: Super Contributor
timestamp: November 04, 2020, 05:43:06 pm
content: No, a long run of RG-6 at 2.4 GHz is not a good idea. For example, 100 feet of RG-6 will have a loss of 79 dB at 2.4 GHz.Ten feet is more manageable as the loss is only 8 dB.

author: jack9
author_rank: Newbie
timestamp: November 15, 2020, 01:29:46 pm
content: sorry for the late reply. i have been busy making the antenna. to keep the cable run as short as possible, i have done some improvisation. but have been unable to get the router(RP-TNC connector) to detect the antenna. so i do not know if the improvisation is the cause of the problem. kindly see attached photos and advise. thanks

author: E Kafeman
author_rank: Regular Contributor
timestamp: November 17, 2020, 04:26:22 pm
content: That antenna dipole is not matched to 50 Ohm and that antenna connector is more an example how to not do it.It will be lossy at 2.4 GHz. At 2.4GHz will it be 1000 times worse and it can in worst case harm your router due to the rather terrible and unstable connection and TNC center pin is maybe not much center any longer.I do design my own antennas but this kind of antenna is too cheap to buy at AliX compared to buying needed raw aluminum material.https://www.aliexpress.com/item/1005001638278047.htmlBuy an adapter between antenna RP SMA connector and RP TNC connector, it will improve performance very much compared to current connection.https://www.aliexpress.com/item/4000910763133.htmlCheck if router antenna input have survived before buying a new antenna for it.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: November 17, 2020, 05:17:01 pm
content: that's clearly an example how to not do it!I would advise you to watch out for a so called Cantenna; they are much easier to construct than a yagi for that frequency. So far I built me a yagi for 23cm, what is a little number bigger than for 13cm, but it's a delicate work which also requires measurement devices like a VNA to verify the result.

author: Yansi
author_rank: Super Contributor
timestamp: November 17, 2020, 05:57:32 pm
content: Quote from: Sal Ammoniac on November 04, 2020, 05:43:06 pmYou probably mix and match feet and meters and the OP mixes 50 and 75ohm.RG-6 is a 75ohm coaxial cable. WiFi uses 50 ohm cabling.RG-6 is pretty much suitable for WiFi, except for the impedance. 100m at 2.4GHz is about 35-40dB loss (or just about 12dB per 100ft, if you want). Loss of 80dB at just 100ft is pretty much nonsense, with this kind of attenuation, you'll likely have trouble even with yo SAT TV, which is what these cables are used for too. Even damn stupid RG58 with solid PE dielectric has just about 60dB/100ft loss at 5 freaking GHz!For wifi, get an LMR-195 or similar cable, that is better than RG58. Remember: The longer the feed, the better coax you need.

author: ardf
author_rank: Contributor
timestamp: November 17, 2020, 07:00:28 pm
content: Looking at the attached images I think it's trolling.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 17, 2020, 10:13:10 pm
content: Quote from: ardf on November 17, 2020, 07:00:28 pmhow do you know that? when people post a picture to show how its done, then it got commented "its not how its done". what picture that is not shown, or people dont care to show is... "how its done properly"... googling we can see a lot of pictures how its done including this one...fromhttps://duo.com/labs/tech-notes/the-yagi-uda-antenna-an-illustrated-primerso you people have something better to show? or a blog? which one is trolling? pictures or words?

author: HB9EVI
author_rank: Frequent Contributor
timestamp: November 17, 2020, 10:47:25 pm
content: are you serious about that?as far as I see the pics of the TO show a piece of wood serving as antenna boom. Sure, people make dumb things if they're not familiar with RF, but to say anything different than this it's not the way how to do it, then what? I'd have plenty of articles from the Dubus magazine which illustrate how such setups like the one you show are failing when closely analyzing them, but you cannot post copyrighted material here.like I said, a yagi for this band is e project for the advanced constructor; a cantenna is almost failsafe as long as you're not just born with two left hands

author: cdev
author_rank: Super Contributor
timestamp: November 17, 2020, 11:17:31 pm
content: I would ditch the Yagi and make a biquad antenna instead.In the distant past (back when I speht a lot of time in nearby cafes and needed to use my home Internet connection, as I did not want to pay for theirs) I made several biquad antennas based on designs I found on the web.I still have one of them and I went back recently to see how well it resonated since now I have a vector network analyzer.. It was spot on.A biquad is very simple, as long as you get the measurements and use the right kind of wire. (i use approximately 1 mm copper wire thats used in most of the house wiring here now.Basically the driven element is a piece of wire bent into two squares and fed in the middle.In fact, you might be able to use a biquad element as your driven element for this antenna. However, here is the thing, if the two sides are going out on the sides, you feed the biquad in the middle and its a vertically polarized - not a horizontally polarized antenna.Its entirely possible that the addition of directors to your biquad in the appropriate polarization will give you an antenna with a lot more gain, if that's what you want, it also solves your matching problem as nothing could be easier than bending the wire to the right shape. I would consider that.Its very forgiving and has a substantial enough amount of gain to support a fairly decent range without needing any fancy equipment to build. Even without directors, just a reflector at the right distance, which is 1/4 wavelength of 2.4 GHz. That you may need to tweak a bit.You could also use a corner reflector which has the advantage of having the distance be non-critical, Just make sure you remember that a biquad's polarization is the direction represented by the two feed points, so even though some might think it was horizontal, its actually vertical.Again, what you'll end up with should fit well into your mental box of what TV antennas look like, because all these designs are a well explored space used frequently for commercial TV antennas..If you plan to build antennas, and have a spare $75 or so, you should consider going to Tindie.com and buying a nanovna 2 from its designers. That money is money well spent as its not just a fantastioc deal its literally a spectacular one, and you will have a very powerful tool for evaluating things like that antenna you made and nothing will tech you faster what happens, at least in the impedance matching and resonance domain. (However it cannot test the gain and pattern for you, that is just as important) .But you'll have the best tool you could possibly find without spending literally what a car cost a few years ago. and literally never have to buy a commercial antenna again, most likely.Consider a biquad. The basic biquad with reflector will give you around 6-7 dbi gain but you can also make a double biquad which will give you "twice" that (3 db more) Basically it depends on what the pattern you want is, how wideIf you are determined to build a yagi, go for it but the matching part, the driven element, is the critical point. I would use a jpole like matching section, shape the driven element just like a j, with the feedpoint adjustable. There is where the nanovna2 would be useful because otherwise how do you determine the exact right spot to feed the Yagi? Depending on every little thing, that feed point may vary significantly. You would need to build or buy a directional coupler, a decent directional coupler is going to cost you, right there half of what the nanoVNA2 would cost you.Wifi access points also don't have the power to work with a typical ham directional coupler. Ham SWR meters which might start at $20 used when you include shipping, (there are also some fairly decent new ones on ebay for not too much, which is cheaper than building them yourself because the cost of the magetic materials would put you uo there. ) are designed to work with ham equipment, not wifi equipment. You need something much more sophisticated to measure something without transmitting power that requires a license to do.So you really cant lose buying one if you have any intention of making more antennas.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 18, 2020, 12:01:33 am
content: Quote from: HB9EVI on November 17, 2020, 10:47:25 pmso the internet is filled with dumb things, the proper and intelligent thing is copyrighted. the one built by the people who read copyrighted materials is no picture. good to hear this! we should go buy books, the one thing that i will encourage anyway. cheers

author: fmkit
author_rank: Contributor
timestamp: November 18, 2020, 12:56:10 pm
content: my tuned antennas made for RC FPV drones and cars, 4km range (0,5w video)

author: cdev
author_rank: Super Contributor
timestamp: November 18, 2020, 07:21:58 pm
content: Quote from: fmkit on November 18, 2020, 12:56:10 pmFmkit, your use of the flashing copper (sheeting) is a really good idea. I've never seen that done before but I'm sure it increases the bandwidth substantially.That might do the trick for the OP.Making it not require tuning assuming he used the same materials and targeted the same frequencies.Another work around for the lack of tuning instruments would be afrequency independent antennawhich could be as simple as a log periodic made with two zigzag shaped pieces of PCB or even just zig-zagging wire..Also it would be easy to have it work on both 2.4 GHz and 5.6 GHz.See the attachments and links. Also see the discussion re infinite balun.https://imageevent.com/holl_ands/zigzaglpa/fmstackedzigzagAlso Cebik "A Tale of Three LPAs"http://on5au.be/content/lpda/zzlp1.pdfSimilar antennas (wrapped inside a triangular radome) are available really cheaply on aliexpress or ebay, because they are widely used as cellphone antennas.You can also make the traditional LPDA on a single sheet of PCB. Ive attached a PDF on the differences.Basically, an LPDA of any kind is an antenna you can use for almost anything that requires a linear polarization directional antenna in that frequency range. Depending on how its built its gain is around 7-9 dbi so around the same as a three element Yagi.Fmkit, you might be interested in circular polarization antennas for FPV - an interesting antenna is the conical logarithmic spiral antenna, which is the circular polarization version of the LPDA.Circular polarization between two circular polarization antennas gives you a bit of an edge over noise and its more resistant to fading.See Dyson, who has written extensively on them. I could post some stuff on that.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 18, 2020, 08:20:38 pm
content: Quote from: fmkit on November 18, 2020, 12:56:10 pmdo you mind to share your reference? 4km GHz signal is something.. something that i want to achieve

author: fmkit
author_rank: Contributor
timestamp: November 18, 2020, 08:52:34 pm
content: 2527MHz video channel does the trick

author: E Kafeman
author_rank: Regular Contributor
timestamp: November 19, 2020, 05:03:45 pm
content: Quote from: Mechatrommer on November 17, 2020, 10:13:10 pmIf a folded dipole is directly connected to unbalanced coaxial cable, then is it not any longer an good antenna, it is just random wires. Your attached photo is a such example.A resonant folded dipole impedance is around 200-300 Ohm.A coaxial cable intended for WiFi have an typical impedance of 50 Ohm.Directly connecting a such cable to a folded dipole is an example of something very bad impedance-matched.That is what your photo is showing, a real bad design done by someone that maybe have read a blog about that this design may work just as good as a proper impedance matched design.Your example athttps://duo.com/labs/tech-notes/the-yagi-uda-antenna-an-illustrated-primercontains incorrect information. Stay away from this type of blog.Author is either lying or can not measure correctly when he is stating 7 dB gain which also shows his lack of knowledge in several ways.There is nothing like "dB gain"which author states that he have measured. dB is a math expression, not a measurable amount. Author do not seems to have any clue at all.More correct, dBd or dBi are a measurable units, which refers to an absolute reference, often used when expressing antenna gain.A three element Yagi-Uda connected in shown way with that terrible coaxial connection, will never result in 7dBi gain. Not the slightest possibility.The part author writes about “constructive interference” had more wrongs then word. Wikipedia is way more correct.Author is clearly trying to trolling people by his homemade redefining of antenna parameters without checking a basic textbook and stating that these antennas will work as described, which they not can.Seems that no one longer care to read a proper book about antenna design, at least learn as much as needed to properly feed a Yagi-Uda dipole with an unbalanced coaxial cable.That blog or your photo.. No that is not a good way to get correct information, obviously.A sidenote, at 2.4 GHz is moisture inside a coaxial cable causing very high attenuation. Never leave cable braid open for rain or moisture if using antenna outdoor as rain will permanently harm a coaxial cable internally and makes it hard to make dry again due to capillary force which quick will spread moisture long way inside cable.

author: fmkit
author_rank: Contributor
timestamp: November 19, 2020, 08:41:13 pm
content: 2.5GHz

author: cdev
author_rank: Super Contributor
timestamp: November 23, 2020, 02:21:30 am
content: Good ways to make cheap Yagis.https://ftp.unpad.ac.id/orari/library/library-sw-hw/amateur-radio/vhf/2m-yagi-antenna/Cheap%20VHF-UHF%20Antennas.htmBelow there are two ways to feed them.Also, what kind of coax to use?Very thick, unless its very short. Most of my patch cables are very short for the reason that coax eats up signal fast at GHz frequencies. I have a few longer cables for SDR use, but I mostly only use them for HF.You should try to put your AP right near the antenna.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 23, 2020, 10:25:05 am
content: Quote from: cdev on November 23, 2020, 02:21:30 ambe ready for "thats not how you do it", no balun?... "be carefull about that blog the author had no clue".. i admit this is a black magic to me all i can do is snap something and see how it respond in VSWR/VNA plot.Quote from: fmkit on November 18, 2020, 08:52:34 pmi'm sorry but this is not helping friend. thanks for your yagi antenna anyway, could be an inspiration.

author: E Kafeman
author_rank: Regular Contributor
timestamp: November 23, 2020, 11:48:43 am
content: >be ready for "thats not how you do it", no balun?If impedance matching is good will a balun not add any advantage at all.Linked "Cheap Yagi" shows a very common way to avoid need for a balun but I have else not checked any promised performance or if calculations are correct at that webpage.Showed dipoles needs mechanical adjustment to give good impedance match but it is often good enough using a simple VSWR-meter or very detailed follow averifieddesign. Verified=Measured with real instruments in a correct measurement setup.A lot of radio-amateurs build these kinds of antennas as it is a simple antenna to tune for an impedance not too long away from ideal 50+j0 Ohm and if untuned but reasonable well built will result still be rather ok.Preferred measurement tool for tuning a such dipole is a VNA measuring both resistive and reactive load.It is a way better tool then just a VSWR-meter for tuning and it will also show changes in bandwidth due to different ways to tune the antenna.A VNA is now a tool within reach for many as cost have dropped and is now in same range as I paid for my first VSWR meter, $50, 30 years ago.A $50 VNA is not a professional tool for several reasons, but it is good enough for this kind of tuning-job and it is a good tool to learn what really is happening when tuning an antenna in different ways with banwidth, gain and efficency.Another thing a VNA can be used for is measuring and confirm that an antenna works just as good and with higher efficiency without balun then with balun if correct tuned.

author: cdev
author_rank: Super Contributor
timestamp: November 23, 2020, 02:15:01 pm
content: I am unable to figure out from the OP's photos exactly what his antenna is. But I have all the components that go into a Yagi like his, and a SAA2, (better known as NanoVNA2).To show how one would tune it, I'd be happy to build a little 2.4 GHz yagi.Just a note on baluns. I've tried to build ferrite baluns that worked at 2.4 GHz. I do have appropriate ferrite beads.. (very small) and insulated magnet wire, but 2.4 GHz is too high for this to be easy.Its not easy to build baluns for frequencies that high.I don't have any real test equipment that works at 2.4 GHz besides my nanovna.Two wireless access points can be used to test a wifi antenna. (attenuators are helpful, too)