2.4GHz antenna replacement - Page 1
Forum section: electronics / rf-microwave

author: IvoS
author_rank: Frequent Contributor
timestamp: September 07, 2020, 06:49:01 pm
content: I have ALIGNA10 transmitter(RC hobby) which I believe is rebranded FUTABA that transmits on 2.4GHz.The antenna on the radio broke off. The quick fix would be to replace it with 2.4GHz antenna with a SMA connector as for examplethis onefound on Amazon.or this one. The question is: is it OK to pick any 2.4GHz antenna and it should work or do I have to look for some other specifications? Thanks in advance.

author: bob91343
author_rank: Super Contributor
timestamp: September 07, 2020, 08:53:49 pm
content: It's not easy. The antenna impedance is important, as well as its bandwidth and center frequency. It takes a vector network analyzer to characterize an antenna, complicated by the difficulty in making proper connections and providing suitable environment.Unless you have a million dollar environmental antenna field test setup, I would recommend just trying different antennas to see how well they work.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 07, 2020, 11:34:18 pm
content: Quote from: IvoS on September 07, 2020, 06:49:01 pmyou basically paying $9 for reselling fee and the nice enclosure and sma connection. inside there is just a small dicky wire you can make out of a coax cable... how effective we cant tell exactly, but i'll say, not very... it can work to some extend, but not very...i guess good antennas take fancy (techy) shapes that less entertaining to the normal joe, such as the simplest one is dipole antenna... it'll be a little bit funny to put on your futaba Tx but some people/youtubers did this and control their rc plane kilometers away...i figured sometime ago putting the arms at 120 degree apart worked charming in term of impedance/vswr, havent test it in real application since i havent got myself back into the rc fun. once upon a time people used vswr meter to do it at affordable price but now we have a vna at cost like $50 (nanoVNA V2N 3GHz).. a serious tool way more than just making an antenna.

author: fordem
author_rank: Regular Contributor
timestamp: September 08, 2020, 12:26:08 am
content: More out of curiosity than anything else, but, what is your antenna design & construction experience like?Quote from: Mechatrommer on September 07, 2020, 11:34:18 pmThat "dicky wire" antenna is actually a center fed vertical dipole with very similar performance to the one below it - just in a more compact, easy to use form - one 1/4 λ element is the exposed center conductor of the coax, the other 1/4 λ element is the tubular sleeve that's over the coax - together they form a 1/2 λ dipole - fed at the center point. This type of antenna is very common on indoor WiFi routers

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 08, 2020, 01:53:45 am
content: Look up "biquad antenna" for how to build your own out of copper wire.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 08, 2020, 02:10:10 am
content: Quote from: fordem on September 08, 2020, 12:26:08 ami'm not an expert, my experience is like only few weeks on a wireless door bell project... i havent gotten back into my rc plane project, all parts, transmitters receivers, BLDC/ESC drivers, motors and propellers bought few years ago. i built a 3d printed plane that crashed few seconds on its first flight testtook many weeks to build it just to see it disintegrate in split second, and then i dont have a chance to build another one again. my 5.8GHz wireless video got broken (my conclusion due to mismatched/crap/hunglow antenna) and bought the replacement front end amplifier, but never gotten to solder/repair it back, those experience is what drove me to find few devices up to 6GHz BW. enough mumbling, what i can really certain, from short experience and advices from people in the internet is... you cant design an antenna effectively without a measurement device, and those are like VSWR, VNA or spectrum analyzer things like that. without those you can only do the field test, ie actually playing with it and see how far can it go. try to build one and hoping it can do well is like walking in the dark with many deep holes everywhere, the chances that you can do it right in the first try is like 1 in a million. ymmv.Quote from: fordem on September 08, 2020, 12:26:08 amiirc, my vna didnt tell me that, at least on hunglow antenna similar to whats linked by OP, but i can never know what exactly he will get, maybe the one he will get is built with specifications as you've mentioned i'm not sure.. simply put, if the performance is the same, there is no need for me to built my 120 degree dipole. i can snap a picture i have one lying around but i dont think its worth it if you never ask, i have few fancy GHz antennas incl mushroom here bought from China and i can tell you they are all crap in term of what a VNA can read. cheers.edit: and i forgot that i also built a small yagi antenna for a 2.4GHz broadband dongle that kind of worked with hunglow coax cable long before i bought my VNA, using plan and formula guidance in the net, i cant remember if i ever put it on the VNA test, it was dismantled when i upgraded my ISP to telephone line (now is fiber)

author: Jwillis
author_rank: Super Contributor
timestamp: September 08, 2020, 02:48:28 am
content: The antenna on your A10 transmitter needs to be dual band . Neither of those will work.

author: TheSteve
author_rank: Unknown
timestamp: September 08, 2020, 04:20:50 am
content: The A10 appears to be 2.4 GHz only.So there should be no need for a dual band antenna.You mention the original broke off - does that mean it doesn't use a connector on the antenna itself? I know my Futaba 4pk super uses a proper sma connector for the antenna(wifi antennas are typically rp-rma).

author: IvoS
author_rank: Frequent Contributor
timestamp: September 08, 2020, 10:50:35 am
content: Quote from: TheSteve on September 08, 2020, 04:20:50 amExactly. No connectors anywhere. Tiny coax goes from antenna to the PCB transmitter module and it is soldered.

author: thinkfat
author_rank: Unknown
timestamp: September 08, 2020, 12:00:04 pm
content: Quote from: IvoS on September 08, 2020, 10:50:35 amCoax wire might(!) imply the system impedance is 50 Ohms. Or they just didn't care enoughOr it's part of a matching network (then the length of the coax would matter). How does the antenna look like?What I'd do - solder an SMA connector to the wire stub of the broken-off antenna, hook it up to a VNA, sweep the 2.4GHz band, see if you find a resonance where it should be. The VNA might also be able to tell you something about the impedance of the antenna, but keep in mind it'll only see it "through" the coax cable stub.Keep a free area around the antenna during the test. Half a meter is probably enough. Don't let it lie on the table, prop it up somehow so that it's upright.

author: TheSteve
author_rank: Unknown
timestamp: September 08, 2020, 04:11:20 pm
content: There is no need for a VNA. The system is 100% 50 ohms. If the coax is soldered to the PCB you'll need to replace it with one that has an SMA or RP-SMA on the other end, mount it on the transmitter and then buy a 2.4 GHz antenna like you've linked previously and screw it on.If it does have a connector on the PCB end it is most likely a u.FL or equivalent.Feel free to post pictures if you need further help.

author: IvoS
author_rank: Frequent Contributor
timestamp: September 08, 2020, 09:37:39 pm
content: Thank you everyone for suggestions. The internals of radio can beseen hereThere are 2 antennas on this radio. The one that sticks out-broken off and one is hidden in the handle.See the pics. I will cut the coax somewhere close to the broken antenna, order SMA connector from digikey and solder the coax to it. I will try that cheap antenna from Amazon and see what happens. My equipment goes only 300MHz high, I have no VNA.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 08, 2020, 11:09:17 pm
content: feel free to repeat history and report back here, that can bring back joyful memory, thats how we grewwe cant recommend what you are intending to do here in this forum as someone from TEA " the wannabe" division will break in and smack around... cheers.

author: TheSteve
author_rank: Unknown
timestamp: September 08, 2020, 11:54:05 pm
content: Should work fine. The coax is very delicate though, and it easy to melt the center insulation. Do make sure the antenna and jack you get match - sma vs Rp-sma can be a pain and stuff on Amazon may not be listed correctly. A connector at Digikey will be of course.And when done do extensive range testing, if it's good then enjoy flying again.

author: MicroBiggerThanMM
author_rank: Contributor
timestamp: September 12, 2020, 02:07:47 am
content: Well, I wouldn't call the OEM antenna a ripoff, I'd call it subsidizing the $10K compliance testing they were forced to shell out to be legally allowed to sell the thing to you. And to pay for marketing wank words.

author: cdev
author_rank: Super Contributor
timestamp: September 12, 2020, 10:50:25 pm
content: You should explain more about how youre going to use it. For RC? if so, you should consider a pair of appropriately circularly polarized antennas. Pinwheel antennas are popular for 2.4 GHz video. Search on FPVQuote from: IvoS on September 07, 2020, 06:49:01 pm

author: richnormand
author_rank: Unknown
timestamp: September 14, 2020, 10:36:29 pm
content: Various comments in this thread have prompted me to put my ASUS WiFi router antenna on the VNA to get a better idea about build, sensitivity, matching etc..I assume both antenna (outside whip and the one in the handle) on the remote are in the WiFi band but I could be wrong.Used proper adaptor for the RP-SMA for the antenna.One photo shows the antenna as originally used. The two bars are the WiFi 2.4G band. Blue trace is mag S11 and redtrace at the bottom in group delay S11. Span is 1.7 to 3.0 GHz. Note the dip at the band location.I usually do these outside but it was raining so there is no proper spacing and reflections at the antenna but the goal was to test the parameter sensitivity when use as described here with the RC controller.Next is just removing the plastic and looking at the insides. Note the change in response just removing the plastic container. This was very repeatable and consistent without any geometry change.Two copper cylinders, one connected to the centre of the coax and the other to the shield make a small dipole in the middleFinal pix look at just putting a small pill plastic bottle on top and getting better match results ....In conclusion apart from doing a lot of work I would think getting a few cheap antennas and trying them is you best bet.... just moving around your remote will change it's characteristics anyway.

author: thinkfat
author_rank: Unknown
timestamp: September 15, 2020, 12:31:34 pm
content: Clearly, that plastic tube is transparent only at much, much higher frequencies ...