Ideal wifi aerial length - Page 1
Forum section: electronics / general

author: Simon
author_rank: Unknown
timestamp: December 22, 2011, 06:51:42 pm
content: What is the ideal length for a WiFi adapter aerial, I have bought a usb adapter with anaerial on and it unscrews so I can change it, it is 3 inches, I have put on one of my router aerials that is 6 inches, does this help ?

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 22, 2011, 07:28:30 pm
content: The bigger the better (usually) but it needs to be designed for a good impedance match at whatever frequency you're running on.

author: 8086
author_rank: Super Contributor
timestamp: December 22, 2011, 07:38:59 pm
content: From my limited knowledge of the subject, assuming 2.4GHz, it sounds like you had a 1/4 wavelength antenna (31.25mm), a 1/2 wavelength antenna (62.5mm) should work better.

author: ejeffrey
author_rank: Super Contributor
timestamp: December 22, 2011, 08:06:42 pm
content: Probably the longer antenna has higher gain. Keep in mind that antenna gain goes hand-in-hand with directionality. High gain omnidirectional antennas transmit in in a narrow pancake -- they go 360 degrees but are still highly directional if you consider all three dimensions.

author: Simon
author_rank: Unknown
timestamp: December 22, 2011, 08:25:33 pm
content: so the longer one has more gain but has a narrower "field" in the 3 dimensional sphere reducing it to more of a disc than sphere ?

author: sub
author_rank: Regular Contributor
timestamp: December 22, 2011, 08:49:49 pm
content: If you're only adjusting the length, though, that will affect the impedance match---you might need to take some measurements to find the best solution.Could you not just adjust it to whatever provides the maximum SNR at the receiver?

author: benemorius
author_rank: Regular Contributor
timestamp: December 22, 2011, 09:08:27 pm
content: Quote from: Simon on December 22, 2011, 08:25:33 pmExactly. The longer one doesn'tnecessarilyhave more gain, but if it does then yes both the receive sensitivity and radiation pattern are sacrificed in the vertical direction in order to be improved horizontally. Likethis. The higher the gain, the flatter the disc.

author: Simon
author_rank: Unknown
timestamp: December 22, 2011, 09:08:53 pm
content: I have nothing to measure with. The best I can do is take both aerials with me to work and try them in turn, My bench is so far from the router at work that I'd probably start to see some change in signal strength, as it is there was a marked difference between my internal one and the external usb one

author: ipman
author_rank: Regular Contributor
timestamp: December 24, 2011, 10:45:12 am
content: You have to measure WSWR, or reflected power. This is wasted power which did not go into antenna because of impedance mismatch between radio and antenna.Altough the longer the better, I did not hear yet about antennas longer than lamba (altough I am no microwave expert).

author: Simon
author_rank: Unknown
timestamp: December 24, 2011, 11:23:28 am
content: Well I tried the two aerials at work, no difference, but then my router is a crap one made by tenda (seriously never touch them) so it could even have the same gain although it's longer. There are some 12 dB aerials on ebay

author: ipman
author_rank: Regular Contributor
timestamp: December 24, 2011, 03:53:10 pm
content: Bear in mind that if you have a weak connection, you should improve both ends. Only one end will not improve things alone, altough a higher gain antenna will compensate somehow for a weak signal.You may want to do a spectrum analisys and choose the least ocuppied channel. Some access points can be tricked into channel 14 by selecting "Japan" as location, this will improve your connection because this channel may be free (altough overlaps).

author: Simon
author_rank: Unknown
timestamp: December 24, 2011, 03:56:10 pm
content: well I have no equipment and the workplace is not setup for people bringing laptops. I just bring my laptop in now and then and "borrow" the unsecured connection. I often loose the connection or it stays connected but looses bandwidth and then comes back, I'm guessing due to people moving around and possibly blocking the signal. It works a lot better than the internal laptop addapter and is an n type rather than g so more up to date in specs.

author: ipman
author_rank: Regular Contributor
timestamp: December 24, 2011, 09:12:15 pm
content: At least try a directional antenna.

author: Simon
author_rank: Unknown
timestamp: December 24, 2011, 09:17:10 pm
content: yea I was thinking that, mind you it works as is with 44% signal and 90% signal integrity so probably not worth worrying

author: ipman
author_rank: Regular Contributor
timestamp: December 24, 2011, 09:28:23 pm
content: A directional antenna will decrease the noise and raise the Signal to Noise Ratio, which is a side benefit of gain. That should do wonders in case you have another close sources on the same channel.Packet loss usually indicates excessive collisions, a sign of another AP on the same channel.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 24, 2011, 11:17:53 pm
content: A good directional antenna would probably help. Your problem might be the AP seeing a lot of noise, even though your adapter isn't. (That's also why greater transmit power on only one end is sometimes useful.)

author: ipman
author_rank: Regular Contributor
timestamp: December 25, 2011, 09:04:49 am
content: Mike, how you did determine that the AP was receiving noise and not the adapter?

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 25, 2011, 01:48:10 pm
content: The adapter reports a good signal but the connection is still unreliable.

author: ipman
author_rank: Regular Contributor
timestamp: December 25, 2011, 02:48:13 pm
content: No offence, but since when a good signal is also an indication about lack of noise?

author: Simon
author_rank: Unknown
timestamp: December 25, 2011, 09:58:02 pm
content: well the "signal quality" is pretty good too well over 80% so I'm guessing that is sort of a signal to noise indication ?

author: vk6zgo
author_rank: Super Contributor
timestamp: December 26, 2011, 02:17:19 am
content: Quote from: benemorius on December 22, 2011, 09:08:27 pmNot quite,If you make the vertical antenna too long,most of the response tends towards "straight up in the air"---in other words along the longitudinal axis of the antenna.These antennas are,perforce,a compromise of:-(1)Just enough performance to work in the usual environment(2) Convenient sizeA directional antenna sacrifices the convenience factor,so can be designed for best performance as regards forward gain,front-to-back ratio,etc.If you want to pursue an interest in antennas,many Amateur Radio websites give good background information on these devices.VK6ZGO

author: Simon
author_rank: Unknown
timestamp: December 26, 2011, 08:34:42 am
content: No I didn't want to go that deep into it just make some marginal gains which are enough to get it working which it seems to quite well.

author: ipman
author_rank: Regular Contributor
timestamp: December 26, 2011, 07:33:03 pm
content: Simon, wireless low-level troubleshooting is not an easy task, especially when interference is showing from time to time.A spectral analisys is the right way to troubleshoot, but this requires some equipment.I was just questioning the judgment about the good signal means that we don't have noise, which is wrong in my opinion. Signal level and background noise should be measured individually, and each one of them has benefits and drawbacks.For example, a directional antenna has gain on some direction, and will just "ignore" signals from certain directions. You will benefit from this by lowering the noise your adapter hear. And by noise I mean signals in which your adapter is not interested, but still receives them anyway.

author: Simon
author_rank: Unknown
timestamp: December 26, 2011, 07:40:24 pm
content: right well yes I'm not equipped or that knowledgeable and as I'm just borowing work wifi as and when available I seem to have found a good compromise of effort versus return. Radio played non stop over the net the other day so can't be bad, I thinking people moving around blocking the signal is the bigger problem now and I can't help that

author: sonicj
author_rank: Frequent Contributor
timestamp: December 27, 2011, 11:02:38 pm
content: i have been using hacked firmware routers since the early days. one of the advantages to that is the ability to run any of the hundreds of available linux packages assembled by clever devs over the years. "wavemon" is a handy lil tool that gives you a simple bargraph for link quality & rssi, which makes antenna aiming and adjustment fairly straightforward. you can run it remotely from the console over ssh or telnet which allows you to view both routers readings as you fiddle with your adjustments. its not a return loss bridge or swr meter, but can be a quite effective tool for tuning without access to proper microwave test gear.-sj (wd4awb)

author: Simon
author_rank: Unknown
timestamp: December 28, 2011, 08:58:09 am
content: Nice, I guess Tenda routers cannot be hacked ?

author: Sionyn
author_rank: Frequent Contributor
timestamp: December 28, 2011, 10:16:38 am
content: try these guyshttp://www.alfa.com.tw/in/front/bin/home.phtml

author: sonicj
author_rank: Frequent Contributor
timestamp: December 28, 2011, 02:07:53 pm
content: Quote from: Simon on December 28, 2011, 08:58:09 amlooks like some models are hackable.http://www.dd-wrt.com/wiki/index.php/Supported_Devices#Tendaopenwrt is the bare bones linux kit, dd-wrt is much easier for the uninitiated,gargoyleis the best open firmware available imo. not as many supported models though....-sj

author: Simon
author_rank: Unknown
timestamp: December 28, 2011, 02:48:34 pm
content: oh good, mine might be one, will check later, the router is shit and often looses connection, The dongles for it also only work with a tenda router.... Never buy tenda guys, I've never had such a piece of crap: you get what you pay for !

author: Simon
author_rank: Unknown
timestamp: December 28, 2011, 04:07:08 pm
content: yay mine is supported, one of the first to be supported, I'll have a read around and give it a goedit: actually it is not supported, or at least not directly

author: ipman
author_rank: Regular Contributor
timestamp: December 28, 2011, 05:46:56 pm
content: Altough great softwares, Xwrt will not modify your RF hardware, which is the most important factor.Great routers do not come cheap.Anyway, try to select a lower modulation or speed, it will improve things a bit.

author: Simon
author_rank: Unknown
timestamp: December 28, 2011, 05:59:25 pm
content: well problem with my router is i keep loosing wifi link to the PC, strangely with the Tenda dongle all other dongles work fine - like you say: pay for shit: get shit. I'll probably buy a decent router soon and chuck out the stupid dongles with it

author: ipman
author_rank: Regular Contributor
timestamp: December 28, 2011, 06:14:42 pm
content: Take a look atUbiquiti. I have two of them outside and they work for two years without any problems. They are based on Atheros SOC's and they can also run DD-WRT, having 16M flash and 32M RAM.The Bullet type mounts directly on a N-type antenna connector, and that let you choose the antenna of your choice.Nice and cheap antennas are fromInterline.

author: sonicj
author_rank: Frequent Contributor
timestamp: December 28, 2011, 10:29:35 pm
content: the ubiquiti stuff looks like a great deal. i just find their lineup a little hard to decipher. is the airrouter the most up to date "pro-sumer" router/switch type unit? according to their forum, its a AR71xx series @ 400 Mhz 32 Mb SDRAM 8 Mb Flash.i am very pleased with my Buffalo WZR-HP-G300NH running Gargoyle. it uses a AR9132 @ 400 MHz 64Mb of SD 32 Mb of Flash, 2x2 external antennas. probably old news by now..... i have a 8dB collinear antenna attached to a u.fl to sma pigtail which replaces one of the stock antennas. this router/firmware combo has been my most reliable setup to date.-sj

author: Simon
author_rank: Unknown
timestamp: December 28, 2011, 11:58:30 pm
content: well I'm just after something decent to work around my house. I'll probably get a midrange router of reputable make and toss the whole tenda kit on ebay for some other poor bugga to play with.

author: gregariz
author_rank: Frequent Contributor
timestamp: December 29, 2011, 12:09:38 am
content: Quote from: Simon on December 28, 2011, 11:58:30 pmOne quick and simple antenna would just be the quarter wave vertical. (btw due to reflection it theoretically will have the same gain as the longer half wave, however the half wave is somewhat more complicated to match and tune). If you have a signal strength indicator in your software, just cut about a 4cm length of tinned copper wire and attach to whatever mounting connection you have ie sma connection. Make sure the whole concoction is mounted on a metal plane. Then cut down the wire 1mm at a time until your signal strength is maximum. At maximum your antenna will be roughly matched and tuned.

author: Simon
author_rank: Unknown
timestamp: December 29, 2011, 09:04:19 am
content: well the tenda dongles have no antenna, I bought a realtek adapter off ebay with an antenna. I think the issue will connection loss is just crap quality tenda gear, probably a bug in the firmware or something

author: ipman
author_rank: Regular Contributor
timestamp: December 30, 2011, 01:09:49 pm
content: They do have an antenna, altough is a very small one, SMD-style mounted on PCB or even made from traces on PCB itself.Not the best option, but this is to comply to UE directives about non-removable antennas.

author: Simon
author_rank: Unknown
timestamp: December 30, 2011, 01:43:54 pm
content: Quote from: ipman on December 30, 2011, 01:09:49 pmwell I meant no external antenna. Signal strength is fine I think it is a firmware issue, a bug or something. The dongles will only connect to the tenda router and often the connection locks up although at full strength, no other dongle has a problem. I think the dongles are more of a problem than the router and I'l probably get another dongle for the pc first and see if things improve

author: clonecrp
author_rank: Regular Contributor
timestamp: December 30, 2011, 03:32:06 pm
content: I also would think you have to measure WSWR, or reflected power. Wrong antenna could wipe-out the transmitter chip ..Happy New Year...Doug

author: Simon
author_rank: Unknown
timestamp: December 30, 2011, 06:41:21 pm
content: Quote from: clonecrp on December 30, 2011, 03:32:06 pmyea, one good reason I may just leave well alone, it works pretty well out of the box so I'll leave it at that

author: ipman
author_rank: Regular Contributor
timestamp: December 30, 2011, 06:44:18 pm
content: There's no point in measuring reflected power in that USB dongle, and very hard to accomplish. You have to desolder the SMD antenna from PCB or cut the PCB trace before antenna ...On the router side it's another story, but the tools required are expensive.

author: clonecrp
author_rank: Regular Contributor
timestamp: January 02, 2012, 08:18:40 pm
content: I'd say U are right ... so... why not create a field strength meter (or use an android app) use a hunk-o-wire & tune with a variable condenser for max output ... Done !ARRL.org or equiv...?Doug

author: ipman
author_rank: Regular Contributor
timestamp: January 03, 2012, 09:02:36 am
content: And if you find out that you have a huge value, then what? I mean, what can you do?