WiFi Antenna - 2.4 GHz Cantenna & Parabolic Dish Gain Measurements and SWR
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- เผยแพร่เมื่อ 18 ต.ค. 2024
- Revisiting the popular WiFi Cantenna and comparing the gain with zero gain mono pole antennas and a parabolic dish antenna. Each antenna, i.e. the Cantenna and the parabolic dish have about the same amount of gain, from 10 to 12 dB. Combined the gain is about 24 dB.
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I built a very similar "cantenna" years ago to receive Showtime ("Showbiz" at the time) signals over the air. I was able to substantially increase the gain by placing a long rod with a series of elements in front of the can. I mounted the can inside a section of PVC and mounted the rod to an end cap. In my case the rod was 1/4" threaded rod and the reflector elements were metal shingle roofing disks!
I like that new toy David.We learn so much from these videos.
Hi Mike,
Yes, that little vector impedance analyzer is fantastic. I have ordered the HF version of it as this one doesn't go below 137 MHz. These little devices advance so fast that they leave all of the older antenna analyzers in the dust and they just seem to get cheaper. As I said the other day in a post, it is a good time to be a geek but I have to say, I have been lucky all my life in the geek world. PS - I got cataract surgery on my right eye and a "premium"lens put in and I can see little green men walking around on Mars... :-) Seriously, it is fantastic to be able to see like a young fellow again. I hope to have the left eye done soon. Again... wow... the technology of today is amazing.
Thank you for making this video, i made cantenna with dimensions you provided and it works great.
Thanks for letting me know. I am glad your project is working out for you.
ok, got my single antenna adapter and the cantenna works, went from about 12 nodes to over 30
i will have to experiment to optimize the efficiency, thanx for your prior input
Very good. Thanks for letting me know.
Thank you for the great video!! I want to put an esp8266 inside of a polyethylene cistern that is buried under about a foot of dirt to measure the water depth in the tank and have it connect to an access point inside the house. If I have an esp8266 setup as an access point, I can get about -80 to -90 dB of signal out by the manhole of the cistern, but it is not enough to make a connection. I guess I will hafta start digging in the trash for cans, LOL!
Amazing gain!
I am fascinated by your videos and have followed your designs but am confused. In a previous video you said the driven element should be 42 mm from the base of the can, now you say 55mm. Which, please?
My can is just short of 4 inches diameter and 6.5 inches long. Thanks.
I am going to revisit an old dish tonight and install the Cantenna feed horn back on it and make some more measurements and a new video. I think I know which feed horn I used for that posting and staging 42 mm and I will check. My Cantenna is 4 inches in diameter because it fits inside 4 inch thin-walled PVC pipe that I use to mount the feed in the center of the dish so, 4 inches is no design parameter, just what I had to use to make my system work. I have only had the opportunity to examine one feed horn from the vintage and huge (14 feet) dishes of decades ago and I think the feed horn used on them are about 6 inches in diameter. Some of this stuff we see on the Internet is just another regurgitation of some academic paper and it doesn't work worth a hoot. I have obsessively built these things in many different versions and the distance of 1/4 wavelength of the probe from the closed end of the can performs very poorly. Doing the math, a full wavelength at 2.4 GHz is 0.125 meters (125 mm) so a quarter wavelength is 31.3 mm or 1.23 inches. Placing the feed probe that close to the closed end of the 4 inch can does not work very well. At around twice that distance, say, 60 mm or so, it works so much better so I would go with the 55 mm instead of the 42 mm. I am determining all of this by the seat-of-my-pants experimentally so the exact distance is not critical down to the mm. That has been my experience. I have also determined from examining military parabolic dishes that the focal point of the dish should be somewhere around a couple of inches (50 mm) inside the can and not right at the mouth of the can. I keep experimenting and posting and hope that whoever chooses to build these antennas will find some value in my experience and in the end, make the final build to their own tweaking. Nowadays with the inexpensive instruments that we can have, that used to cost multi-thousands of $$$, we can measure and tune these gigahertz devices up as easily as the ham radio operator of yesteryear could his 80 meter dipole. thanks for your comments.
thank you very much
what gain would you get with the cantenna mounted at the right spacing in front of the dish instead of the antenna currently on the dish??
Since I have this dish so nicely set up for the Andrew probe seen in the video, I don't want to change it to the Cantenna feed horn. But, I do have a slightly larger dish that has been set up for the feed horn and the slotted line feed probe which I intend to make another video on maybe even this evening. We might expect a bit more gain out of the larger dish just because of its size but I think, if I remember correctly, the gain is pretty much the sum of the dish plus the feed horn and I expect about 20 dB from this dish. We will see soon. Thanks for your comments.
thank you
Nick Horrex
Thanks for shareing.
First, sorry for hijacking your thread, but youtube only lets me post new ones when it feels like it, now, and I have no idea why. But I built and tested lots of these, and have a lot to say about them.
First, I'm not a mathmatician, or anything, or an expert, except on youtube. I read everything I could find online, and used several online calculators to compute mine. They all absolutely agreed with one another, so I presume their math is sound, even if it is beyond me. And here are the important things about waveguides that I learned are important, We already know that a 1/4 dipole should be about 31 or 32mm. But the diameter of the can and the wavelength BOTH effect the distance from the back of the can it has to go, it's where the standing wave will form. Think of it as the waves come in from the front (and only certain size radio waves will fit properly into a certain size can), and they hit the back of the can, and bounce back into the incoming waves, and pile up on each other. It's called propagation of a standing wave. When I did my sattelite dish feed tests, I decided just for curiosity, I took apart the original feed and was very familiar with what it was. It was a waveguide tube, flared at the open end, much smaller, with about a 1" diameter, except at the back, instead of having a wire feed a certain distance from the back of the can, it had a flat piece of metal cut in the shape of a staircase profile, stepping up to the end that was almost touching the back of the can. So I knew it was a wide band waveguide, how smart is that? And I felt so vindicated! But the main point is that the standing wave point is a factor of both the wavelength, and the diameter of the tube, and it form a curve with wavelenth, like that stepped conductor stepped up towards the back of the tube, in that same way.
For 2.4ghz, or wifi, the wavelength is 12.5cm. The ideal diameter can for this band should be between 80mm and 90mm. Use large soup/sauce cans, they are 3-1/4", about 83mm, those will work the best. And for that diameter, the feed should be placed 2.5" - or 63.5mm from the back of the can. I'm working from memory, but those numbers will build you a good antenna. What I suggest doing, if you can, is elongate your hole, so that you can move it forwards and backwards a little bit, centering it at 2.5", so you can adjust it if you want to. One can will work, but putting on one more, with both ends opened to make it longer would be better. The wavy sides of the can are less than ideal, so I made my last generation from exotic tea tins, with smooth sides, but they are a little outside the ideal size, and work about the same. They look more professional, though. To make my wifi wunderwaffen, I coupled one to a 1 watt USB client (cabled) with an Atheros chipset by way of just an N to RP-SMA adapter, so there is no loss to any coaxial cable. I pick up about 100 AP's in the only direction I have that isn't blocked. Some are a mile from me. It works twice as well on the sattelite dish, but I built a double biquad feed for that that works as well, but isn't as direction sensitive, it's a wider antenna with that.
get this... the radiating pin does not have to be copper, i have one f-connector with a rusty piece of steel wire soldered in and it performs comparably to a copper pin
i built a cantenna..i don't get a lousy signal...i get no signal
The components you use to build it are very important. Use a N connector and not a BNC or UHF (SO-239). A good N connector is good to at least 4 GHz whereas a BNC is rated to only 1 GHz and a UHF connector to 300 MHz. Make the monopole 1.2 inches long and solder it directly to the N connector and connect the cantenna absolutely as close to the access point as possible using large good quality coax like LMR-400. RG-58 and the small coax sold on Ebay will not work. The gain of an antenna can easily be lost in just a few feet of transmission line coax. It is also very directional so make sure it is pointed at the other WiFi device carefully. Hope this helps.
@@ElPasoTubeAmps i used an n connector and a store bought cable....however i am using a twin antenna adapter...is that the problem?
@@thebetazone6955 Is the store bought cable short, like one foot or so and what is it, RG-58, etc? I am not sure what the twin antenna adapter is? Ideally, the cantenna would connect to the WiFi device directly with (mount of top of the WiFi device) with an N to RP-SMA adapter or RP-TNC adapter whichever is on the WiFi device.
When I look up "twin antenna adapter" I see the TV type 300 ohm to 75 ohm transformer for VHF antennas. If that is what you are using, that surely is the problem.
@@ElPasoTubeAmps the cable is about 13 inches and is a n to sma adapter and is very thin.....the adapter has two antennas, which i read elsewhere means there is a dithering algorythm that swtiches between the antennas...the wifi adapter can plug into a wired stand or the the computer at the usb directly